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Long, M.A., Moorkens, E.A. and Kelly, D.L. (2018) A quantitative study on the implications of sieve mesh size in land mollusc sampling – are snails 0.5-1 mm in size worth including? Irish Naturalists’ Journal 36: 1-8.

Accepted for publication: 10 July 2017 Published: 22 June 2018

Irish Naturalists’ Journal

A quantitative study on the implications of sieve mesh size in land mollusc sampling – are snails 0.5-1 mm in size worth including?

Volume 36 Part 1 © Published by the Irish Naturalists’ Journal Ltd, who are not responsible for the views of individual authors expressed herein. Copyright rests with The Irish Naturalists Journal Ltd. and the authors. Editor Nigel Monaghan

*Maria P. Long1, Evelyn A. Moorkens2 and Daniel L. Kelly3 Newtownshandrum, Charleville, Co. Cork 123 Rathdown Park, Greystones, Co. Wicklow 3 Botany Building, School of Natural Sciences, Trinity College, Dublin 2 1

Sectional Editors Professor Tom Bolger Dr Tom Curtis Professor Colin Lawton Dr Ferdia Marnell Dr Tomás Murray Dr Brian Nelson Dr Matthew Parkes Dr Julian Reynolds

2

Terrestrial molluscan samples were processed using 0.5 mm and 1 mm mesh sieves to investigate the numbers and identities of species which would be missed if only the latter size is used. Findings indicate that although there were more than double the number of snail shells in the smaller size fraction, only a relatively small number of species are likely to be missed or under-estimated. However, of the six such species identified, one (a Red List species) would have been missed completely, and a further two would have been grossly under-estimated. Furthermore, on a site by site basis, by the inclusion of the 0.5-1 mm size fraction, a median of two new species was added at each site. The proportions of missed species varied by habitat, with grasslands showing a 42 per cent increase. In conclusion, using a 0.5 mm mesh vastly increases the numbers of shells to process, and these will contain a large proportion of immature and dead specimens which can be difficult to identify and problematic to include in datasets. While only a small number of species are likely to occur in this small size fraction, these species can be missed altogether or hugely under-estimated using larger mesh sizes. However, the species which are likely to be missed or under-estimated can be predicted using published databases which give details on size and, importantly, shape, of shells.

© Cover photograph: Pale and normally coloured juvenile Brown Crabs (Cancer pagurus L.) from the Great Saltee Island. Photo: Alan Hinchy. Publication date 22 June 2018

Keywords: invertebrate sampling; sieve mesh size; terrestrial molluscs; sampling effort; immature and dead shells Introduction

Supporting organizations and grant awarding bodies: Belfast Naturalists' Field Club Dublin Naturalists' Field Club National Biodiversity Data Centre, Waterford National Botanic Gardens, Glasnevin National Museum of Ireland, Dublin National Park and Wildlife Service, Dublin National University of Ireland, Galway Royal Dublin Society, Ballsbridge, Dublin Queen's University, Belfast Praeger Fund, The Royal Irish Academy, Dublin School of Environmental Services, University of Ulster The Heritage Council, Kilkenny Trinity College, Dublin Ulster Museum, Belfast University College, Dublin

The official organ of: Belfast Naturalists' Field Club County Armagh Wildlife Society Dublin Naturalists' Field Club Galway Naturalists' Field Club Irish Geological Association Route Naturalists' Field Club

The processing and identification of tiny and/ or immature invertebrate specimens is timeconsuming, and generally more challenging than dealing with larger or adult specimens. In the case of land snails in particular, but also common in some other invertebrate groups, immature individuals are often lacking in key characters, and few identification keys deal adequately with them. The amount and proportion of small individuals included in samples will depend largely on the sieve mesh size used when processing the samples. A search through the relevant literature revealed that a 0.5 mm sieve mesh was used in most studies on terrestrial land snails (but there were exceptions: e.g. 1 mm in Chatfield 1977, and 2 mm in Menez 2001). The use of a 0.5 mm mesh means that many tiny shells will be included in a sample. In terms of the time implications, Ferraro et al. (1989), in a study of macro-benthic fauna, found that it took approximately 2.5 times longer to process *Corresponding author – [email protected]

samples which were ≥0.5 mm in size compared to ≥1 mm samples, while James et al. (1995) report it taking between 2 and 4 times longer. Considering the amount of extra work involved in processing and identifying tiny individuals, the question of whether all the extra time involved if a 0.5 mm mesh sieve is used is worth it in terms of return is therefore an important one, and one which has not been adequately addressed in the literature, neither relating to land snails or to other invertebrate groups (with the possible exception of freshwater macroinvertebrate communities and fossil assemblages – see Barba et al. 2010, Kidwell 2002, Kowalewski and Hoffmeister 2003). This study involved the collection and processing of 120 samples of terrestrial snails from three habitat types in the west of Ireland. The snails found in the 0.5-1 mm size fraction of these samples were processed separately from those in the >1 mm fraction. This paper assesses which species were missed or underestimated, and by how much, when using only a 1 mm sieve, and discusses whether the extra effort involved in processing the smaller shells was Irish Naturalists’ Journal Vol. 36 Part 1 1

Long, M.P., Moorkens, E.A. & Kelly, D.L.

worthwhile in terms of the data generated. Until now malacologists have lacked quantitative data to make an informed choice in this regard. Materials and methods Study area and design This study was based in the Burren, a karstic region in the west of Ireland, and one which is famous as one of the most biologically interesting and biodiverse areas in Ireland (Osborne and Jeffrey 2003, Viney 2003, Webb and Scannell 1983). However, detailed studies on the land mollusc fauna of the region have been few and those that do exist are largely focussed on single species (e.g. Moorkens and Gaynor 2002, Platts et al. 2003) and/or are unpublished reports (e.g. Moorkens 1999, 2001). Land snails were collected from three habitat types: (i) ash-hazel or hazel woodlands, (ii) areas of hazel scrub/semi-natural grassland mosaic (termed ‘scrub’ in the text), and (iii) seminatural grasslands. These habitats were chosen because they form part of a dynamic continuum in the area, one which is of great interest and current relevance due to recent increases in scrub encroachment rates (Deenihan et al. 2009, Dunford and Feehan 2001, O’Donovan 2001, Comber and Jones 2006). The project of which this work formed part necessitated the setting up of a network of twelve long-term study sites (four each in woodland, scrub and grassland), each with a set of fixed vegetation quadrats. Molluscan samples were taken from immediately adjacent to these fixed quadrats. Field and laboratory methods Sampling was carried out in autumn 2006. Autumn is a good time of year for mollusc sampling as the weather is likely to be suitable – damp but not yet too cold (Cook 2001). It also follows the peak reproductive period of many mollusc species (Falkner et al. 2001), thus ensuring that there should be many individuals present and maximising the chances of a more complete species inventory. In the field, snails were quantitatively sampled using 25 x 25 cm quadrats. Ten of these were collected from each site, giving a total of 120 samples. Within each quadrat all field and ground layer vegetation, litter and loose surface soil were removed and bagged (following Cameron 1982). Studies have shown that the collection of quantitative litter samples (and later sorting in a lab) provides more comprehensive results than direct searching alone (Cameron and Pokryszko 2005, Oggier et al. 1998). Further, it is less destructive than the removal of soil and yields almost as complete a result (Moorkens 2 Irish Naturalists’ Journal Vol. 36 Part 1

Sieve Mesh Size in Land Mollusc Sampling

2003, Oggier et al. 1998). Care was taken while sampling in scrub and woodland to minimise shaking or disturbing overhead vegetation, in order to avoid inadvertently including arboreal species. As is common for many small-sized invertebrate groups, the snail shells in this study were processed by hand in the laboratory using a series of sieves in order to separate them by size (size fractions: 1 mm). The smallest fraction contained only dust and tiny shell fragments and was discarded. The other two fractions were carefully sorted through and searched by eye for snails, which were removed, counted and identified. All adult specimens were identified to species level, and counts of numbers of immature and dead specimens were taken for each quadrat/sample. Specimens were listed as ‘dead’ if the shell was empty, and it was obvious that the animal had been dead for some time. This was ascertained by examining the shell for bleaching, loss of colour/shine and damage to the shell structure. Some shells appeared empty but seemed fresh – these were categorised as alive, and either adult or immature as appropriate. ‘Dead’ specimens were not further subdivided into adult and immature. Any difficulties which arose during the course of lab work concerning determination were resolved either by referral to an expert or by comparison with verified reference collections. Nomenclature follows Anderson (2005). Results Numbers of specimens There were almost 2.5 times as many individual snail shells in the 0.5-1 mm size fraction as in the >1 mm samples (3,726 and 1,572 respectively). The majority of those in the smaller sized samples were immature (53 %), with 20 % adults and 27 % dead (Fig. 1), and there was an average of 31.1 snails per quadrat. These data compare with a much more even spread in the >1 mm fraction, with approximately 40 % immature, 28 % adults and 33 % dead specimens, and an average of 13.1 snails per quadrat. It is clear that the largest proportion of the increased numbers in the 0.5-1 mm size fraction comes from immature specimens. Species missed or under-estimated Only six species were recorded from the 756 adult specimens found in the 0.5-1 mm size fraction (Table 1), compared to 24 species (again, including only adult specimens) from the >1 mm fraction of the same 120 samples. One of the species found in the small size fraction, Acicula fusca (Montagu, 1803), was not recorded from

Figure 1. The average number of snails per quadrat (+/- standard error) from the >1 mm and 0.5-1 mm size fractions, across all twelve study sites.

Table 1. Snail species identified from the 0.5-1 mm size fraction (adults only), with the numbers for the same species from the >1 mm data for comparison. Also given are the number of study sites at which the snails were recorded. Species name

No. of adult individuals in 0.5-1 mm fraction

No. of study sites from which recorded (0.5-1 mm fraction only, max = 12)

No. of adults in >1 mm fraction

No. of study sites from which recorded (>1 mm fraction only, max = 12)

Carychium tridentatum

503

10

7

3

Punctum pygmaeum

138

10

3

3

Carychium minimum

66

4

0

-

Vertigo substriata

20

6

16

6

Acicula fusca

16

6

0

-

Vertigo pygmaea

13

3

27

6

Total

756

-

53

-

any of the samples in the larger size fraction (neither as adult, immature or dead specimen). This species is listed as ‘Vulnerable’ in the Red List for Irish non-marine molluscs (Byrne et al. 2009). There were two sites which had only one species recorded in the 0.5-1 mm size fraction, and in both cases it was Acicula fusca. While Carychium minimum O.F. Müller, 1774, was not found as an adult in the >1 mm samples (Table 1), a single dead specimen was recorded at two separate sites, and so the 0.5-1 mm results do not constitute the only records for the species in this study. Some species showed large discrepancies in the numbers of individuals recorded between the two size fractions (Table 1). For example, over 500 adult specimens of Carychium tridentatum (Risso, 1826) were found in the 0.5-1 mm fraction, from across ten study sites, in comparison to just seven individuals from three sites in the >1 mm fraction. At individual sites, too, there were large differences: 117 specimens of C. tridentatum in the 0.5-1 mm fraction at one of the scrub sites, with no specimens in the >1 mm sample from

that site. Similarly, there were 46 individuals of Punctum pygmaeum (Draparnaud, 1801) at one of the woodland sites, with none in the >1 mm sample. C. minimum too illustrated this type of difference, with 36 adults recorded from a grassland sample but no adults in the >1 mm fraction. Even when individuals of a taxon were present in both fractions, sizeable discrepancies still occurred: 105 compared to four for C. tridentatum in a woodland site, and 21 compared to one for P. pygmaeum in a grassland site. The number of species recorded per site in the >1 mm size fraction ranged from three to 14 (Fig. 2), with a median of twelve. In the 0.5-1 mm fraction the number ranged from one to five, with a median of four. However, in spite of the lower numbers, at each of the twelve sites, at least one new species was added to the site species list by the inclusion of the data from the smaller size fraction. Of the six species recorded in the small size fraction, those which were most often new additions to the species lists for sites were C. Irish Naturalists’ Journal Vol. 36 Part 1 3


worthwhile in terms of the data generated. Until now malacologists have lacked quantitative data to make an informed choice in this regard. Materials and methods Study area and design This study was based in the Burren, a karstic region in the west of Ireland, and one which is famous as one of the most biologically interesting and biodiverse areas in Ireland (Osborne and Jeffrey 2003, Viney 2003, Webb and Scannell 1983). However, detailed studies on the land mollusc fauna of the region have been few and those that do exist are largely focussed on single species (e.g. Moorkens and Gaynor 2002, Platts et al. 2003) and/or are unpublished reports (e.g. Moorkens 1999, 2001). Land snails were collected from three habitat types: (i) ash-hazel or hazel woodlands, (ii) areas of hazel scrub/semi-natural grassland mosaic (termed ‘scrub’ in the text), and (iii) seminatural grasslands. These habitats were chosen because they form part of a dynamic continuum in the area, one which is of great interest and current relevance due to recent increases in scrub encroachment rates (Deenihan et al. 2009, Dunford and Feehan 2001, O’Donovan 2001, Comber and Jones 2006). The project of which this work formed part necessitated the setting up of a network of twelve long-term study sites (four each in woodland, scrub and grassland), each with a set of fixed vegetation quadrats. Molluscan samples were taken from immediately adjacent to these fixed quadrats. Field and laboratory methods Sampling was carried out in autumn 2006. Autumn is a good time of year for mollusc sampling as the weather is likely to be suitable – damp but not yet too cold (Cook 2001). It also follows the peak reproductive period of many mollusc species (Falkner et al. 2001), thus ensuring that there should be many individuals present and maximising the chances of a more complete species inventory. In the field, snails were quantitatively sampled using 25 x 25 cm quadrats. Ten of these were collected from each site, giving a total of 120 samples. Within each quadrat all field and ground layer vegetation, litter and loose surface soil were removed and bagged (following Cameron 1982). Studies have shown that the collection of quantitative litter samples (and later sorting in a lab) provides more comprehensive results than direct searching alone (Cameron and Pokryszko 2005, Oggier et al. 1998). Further, it is less destructive than the removal of soil and yields almost as complete a result (Moorkens 2 Irish Naturalists’ Journal Vol. 36 Part 1


2003, Oggier et al. 1998). Care was taken while sampling in scrub and woodland to minimise shaking or disturbing overhead vegetation, in order to avoid inadvertently including arboreal species. As is common for many small-sized invertebrate groups, the snail shells in this study were processed by hand in the laboratory using a series of sieves in order to separate them by size (size fractions: 1 mm). The smallest fraction contained only dust and tiny shell fragments and was discarded. The other two fractions were carefully sorted through and searched by eye for snails, which were removed, counted and identified. All adult specimens were identified to species level, and counts of numbers of immature and dead specimens were taken for each quadrat/sample. Specimens were listed as ‘dead’ if the shell was empty, and it was obvious that the animal had been dead for some time. This was ascertained by examining the shell for bleaching, loss of colour/shine and damage to the shell structure. Some shells appeared empty but seemed fresh – these were categorised as alive, and either adult or immature as appropriate. ‘Dead’ specimens were not further subdivided into adult and immature. Any difficulties which arose during the course of lab work concerning determination were resolved either by referral to an expert or by comparison with verified reference collections. Nomenclature follows Anderson (2005). Results Numbers of specimens There were almost 2.5 times as many individual snail shells in the 0.5-1 mm size fraction as in the >1 mm samples (3,726 and 1,572 respectively). The majority of those in the smaller sized samples were immature (53 %), with 20 % adults and 27 % dead (Fig. 1), and there was an average of 31.1 snails per quadrat. These data compare with a much more even spread in the >1 mm fraction, with approximately 40 % immature, 28 % adults and 33 % dead specimens, and an average of 13.1 snails per quadrat. It is clear that the largest proportion of the increased numbers in the 0.5-1 mm size fraction comes from immature specimens. Species missed or under-estimated Only six species were recorded from the 756 adult specimens found in the 0.5-1 mm size fraction (Table 1), compared to 24 species (again, including only adult specimens) from the >1 mm fraction of the same 120 samples. One of the species found in the small size fraction, Acicula fusca (Montagu, 1803), was not recorded from

Figure 1. The average number of snails per quadrat (+/- standard error) from the >1 mm and 0.5-1 mm size fractions, across all twelve study sites.

Table 1. Snail species identified from the 0.5-1 mm size fraction (adults only), with the numbers for the same species from the >1 mm data for comparison. Also given are the number of study sites at which the snails were recorded. Species name

No. of adult individuals in 0.5-1 mm fraction

No. of study sites from which recorded (0.5-1 mm fraction only, max = 12)

No. of adults in >1 mm fraction

No. of study sites from which recorded (>1 mm fraction only, max = 12)


503

10

7

3

Punctum pygmaeum

138

10

3

3

Carychium minimum

66

4

0

-

Vertigo substriata

20

6

16

6

Acicula fusca

16

6

0

-

Vertigo pygmaea

13

3

27

6

Total

756

-

53

-

any of the samples in the larger size fraction (neither as adult, immature or dead specimen). This species is listed as ‘Vulnerable’ in the Red List for Irish non-marine molluscs (Byrne et al. 2009). There were two sites which had only one species recorded in the 0.5-1 mm size fraction, and in both cases it was Acicula fusca. While Carychium minimum O.F. Müller, 1774, was not found as an adult in the >1 mm samples (Table 1), a single dead specimen was recorded at two separate sites, and so the 0.5-1 mm results do not constitute the only records for the species in this study. Some species showed large discrepancies in the numbers of individuals recorded between the two size fractions (Table 1). For example, over 500 adult specimens of Carychium tridentatum (Risso, 1826) were found in the 0.5-1 mm fraction, from across ten study sites, in comparison to just seven individuals from three sites in the >1 mm fraction. At individual sites, too, there were large differences: 117 specimens of C. tridentatum in the 0.5-1 mm fraction at one of the scrub sites, with no specimens in the >1 mm sample from

that site. Similarly, there were 46 individuals of Punctum pygmaeum (Draparnaud, 1801) at one of the woodland sites, with none in the >1 mm sample. C. minimum too illustrated this type of difference, with 36 adults recorded from a grassland sample but no adults in the >1 mm fraction. Even when individuals of a taxon were present in both fractions, sizeable discrepancies still occurred: 105 compared to four for C. tridentatum in a woodland site, and 21 compared to one for P. pygmaeum in a grassland site. The number of species recorded per site in the >1 mm size fraction ranged from three to 14 (Fig. 2), with a median of twelve. In the 0.5-1 mm fraction the number ranged from one to five, with a median of four. However, in spite of the lower numbers, at each of the twelve sites, at least one new species was added to the site species list by the inclusion of the data from the smaller size fraction. Of the six species recorded in the small size fraction, those which were most often new additions to the species lists for sites were C. Irish Naturalists’ Journal Vol. 36 Part 1 3


Sieve Mesh Size in Land Mollusc Sampling Table 2. Shell size for species recorded as adults in this study as a whole (data from Falkner et al. 2001, Kerney and Cameron 1979). Species are arranged first by size category from Falkner et al. (2001) and then by maximum dimension from Kerney and Cameron (1979). Species recorded in the 0.5-1 mm size fraction in this study are in bold. We follow the ‘fuzzy coding’ system used by Falkner et al. (2001). It describes the degree of association between a species and a variable - in this case, maximum shell height. A blank cell means ‘no association’, 1 signifies a ‘minor association’, 2 - ‘moderate association’ and 3 - ‘maximum association’. *As this is a recently re-discovered species, data were not available in Kerney and Cameron (1979) nor in Falkner et al. (2001). They were modified instead from Gittenberger et al. (2006). 1 mm and 0.5-1 mm size fractions, along with the number of species in the 0.5-1 mm size fraction which are recorded only in that fraction at that site.

tridentatum (added seven times out of a possible twelve), P. pygmaeum (added seven times) and Acicula fusca (added six times). Overall, a median of two new species was added to each site list, with a maximum of four (at one scrub site) (Fig. 2). In terms of percentage increase to species lists, the lowest addition was equivalent to an 8 % increase, whereas the highest was equivalent to a 75 % increase (from four species to seven at a grassland site). Interestingly, the increase was not homogeneous across habitats, with grasslands showing the largest numbers of added species when the 0.5-1 mm fraction was included (average increases, by habitat: 17 % in woodland, 26 % in scrub, 42 % in grassland). Shell size In order to investigate in more depth the influence of shell size and shape on the identity and quantity of species recorded using differing sieve mesh sizes, data were obtained from Kerney and Cameron (1979) and from Falkner et al. (2001). The latter is a database containing information on many aspects relating to shelled gastropods in western Europe, such as distribution, habitat preference, reproductive traits, food preference and, importantly in this case, morphology. Unsurprisingly, the six species recorded in the small size fraction in this study were amongst the smallest from the species list for this study 4 Irish Naturalists’ Journal Vol. 36 Part 1

as a whole (Table 2). Acanthinula aculeata (O.F. Müller, 1774) was the only species in our list from within the smallest size category provided in Falkner et al. (1 mm in this study, it would seem that numbers alone may justify the use of a 0.5 mm sieve mesh for the sake of completeness, but a number of other factors must be considered. A majority (80 %) of the extra specimens in the small size fraction were immature or dead, and these are problematic in a number of ways. With regard to inclusion of immature invertebrate specimens in studies, if there has been a recent reproductive event for one (or a few) species, there can be very high numbers of immature specimens present in a sample, leading to skewed results, and a possible false impression of the size or composition of a population. In relation to dead shells, and possibly more relevant to snails than to other invertebrate groups, there are also risks. Cernohorsky et al. (2010), in a study aimed at comparing the results of including living only, or living and dead, specimens, found “differential preservation” of shells among sites with differing soil chemistries,

2.5 - 5.0 mm 5 - 15 mm

>15 mm

Max. height (mm)

Max. breadth (mm)

Punctum pygmaeum

3

-

1.5

Vertigo substriata

3

1.7

1.1

Carychium minimum

3

1.9

0.9


3

2

0.9

Acanthinula aculeata

3

2

2

Vertigo pygmaea

3

2.2

1.2

Acicula fusca

2

2

2.5

0.8

Columella aspera

2

2

2.5

1.4

Vitrea contracta

2

2

-

2.5

Columella edentula

3

3

1.5

Euconulus cf. fulvus

3

-

3.5

Leiostyla anglica

3

3.7

1.9

Vitrea crystallina

3

-

4

Aegopinella pura

3

-

4.2

Nesovitrea hammonis

3

-

4.2

Lauria cylindracea

3

4.4

1.8

Vitrina pellucida

3

1

-

6

Cochlicopa cf. lubricella

3

1

6.8

2.5

Balea heydeni*

1

3

7

-

Discus rotundatus

3

-

7

Cochlicopa cf. lubrica

3

7.5

2.9

Aegopinella nitidula

3

-

10

Clausilia bidentata

3

12

2.7

Oxychilus cellarius

3

-

12

Trochulus hispidus

3

6

12

Helicella itala

2

12

25

which lead to distortion of estimates of species richness and abundance. In lime-rich areas shells may persist for many years in a subfossil condition (Cameron 2003), and as such they do not provide evidence that a species is still present at a site (Kerney 1999). Timing of survey work also becomes an issue if dead specimens are to be included. For example, Cameron (1982) reported that they recorded a larger than average number of dead shells at the end of winter, and also in September. In the Burren grasslands, O’Donovan (1987) found a much higher number of empty shells of Helicella itala (Linnaeus, 1758) in

2

September, compared to other times of the year. Thus the relative advantages and disadvantages of including immature and/or dead shells in any study must always be weighed up. With such a high proportion of these categories of individuals in the 0.5-1 mm size fraction, the relative value of processing these (even if the immature and dead specimens are not identified to species) must be considered. As well as the overall numbers of individual snail shells recorded, the identity of the species found in the small size fraction, and their abundance relative to the larger fraction, provides Irish Naturalists’ Journal Vol. 36 Part 1 5


Sieve Mesh Size in Land Mollusc Sampling Table 2. Shell size for species recorded as adults in this study as a whole (data from Falkner et al. 2001, Kerney and Cameron 1979). Species are arranged first by size category from Falkner et al. (2001) and then by maximum dimension from Kerney and Cameron (1979). Species recorded in the 0.5-1 mm size fraction in this study are in bold. We follow the ‘fuzzy coding’ system used by Falkner et al. (2001). It describes the degree of association between a species and a variable - in this case, maximum shell height. A blank cell means ‘no association’, 1 signifies a ‘minor association’, 2 - ‘moderate association’ and 3 - ‘maximum association’. *As this is a recently re-discovered species, data were not available in Kerney and Cameron (1979) nor in Falkner et al. (2001). They were modified instead from Gittenberger et al. (2006). 1 mm and 0.5-1 mm size fractions, along with the number of species in the 0.5-1 mm size fraction which are recorded only in that fraction at that site.

tridentatum (added seven times out of a possible twelve), P. pygmaeum (added seven times) and Acicula fusca (added six times). Overall, a median of two new species was added to each site list, with a maximum of four (at one scrub site) (Fig. 2). In terms of percentage increase to species lists, the lowest addition was equivalent to an 8 % increase, whereas the highest was equivalent to a 75 % increase (from four species to seven at a grassland site). Interestingly, the increase was not homogeneous across habitats, with grasslands showing the largest numbers of added species when the 0.5-1 mm fraction was included (average increases, by habitat: 17 % in woodland, 26 % in scrub, 42 % in grassland). Shell size In order to investigate in more depth the influence of shell size and shape on the identity and quantity of species recorded using differing sieve mesh sizes, data were obtained from Kerney and Cameron (1979) and from Falkner et al. (2001). The latter is a database containing information on many aspects relating to shelled gastropods in western Europe, such as distribution, habitat preference, reproductive traits, food preference and, importantly in this case, morphology. Unsurprisingly, the six species recorded in the small size fraction in this study were amongst the smallest from the species list for this study 4 Irish Naturalists’ Journal Vol. 36 Part 1

as a whole (Table 2). Acanthinula aculeata (O.F. Müller, 1774) was the only species in our list from within the smallest size category provided in Falkner et al. (1 mm in this study, it would seem that numbers alone may justify the use of a 0.5 mm sieve mesh for the sake of completeness, but a number of other factors must be considered. A majority (80 %) of the extra specimens in the small size fraction were immature or dead, and these are problematic in a number of ways. With regard to inclusion of immature invertebrate specimens in studies, if there has been a recent reproductive event for one (or a few) species, there can be very high numbers of immature specimens present in a sample, leading to skewed results, and a possible false impression of the size or composition of a population. In relation to dead shells, and possibly more relevant to snails than to other invertebrate groups, there are also risks. Cernohorsky et al. (2010), in a study aimed at comparing the results of including living only, or living and dead, specimens, found “differential preservation” of shells among sites with differing soil chemistries,

2.5 - 5.0 mm 5 - 15 mm

>15 mm

Max. height (mm)

Max. breadth (mm)

Punctum pygmaeum

3

-

1.5

Vertigo substriata

3

1.7

1.1

Carychium minimum

3

1.9

0.9


3

2

0.9

Acanthinula aculeata

3

2

2

Vertigo pygmaea

3

2.2

1.2

Acicula fusca

2

2

2.5

0.8

Columella aspera

2

2

2.5

1.4

Vitrea contracta

2

2

-

2.5

Columella edentula

3

3

1.5

Euconulus cf. fulvus

3

-

3.5

Leiostyla anglica

3

3.7

1.9

Vitrea crystallina

3

-

4

Aegopinella pura

3

-

4.2

Nesovitrea hammonis

3

-

4.2

Lauria cylindracea

3

4.4

1.8

Vitrina pellucida

3

1

-

6

Cochlicopa cf. lubricella

3

1

6.8

2.5

Balea heydeni*

1

3

7

-

Discus rotundatus

3

-

7

Cochlicopa cf. lubrica

3

7.5

2.9

Aegopinella nitidula

3

-

10

Clausilia bidentata

3

12

2.7

Oxychilus cellarius

3

-

12

Trochulus hispidus

3

6

12

Helicella itala

2

12

25

which lead to distortion of estimates of species richness and abundance. In lime-rich areas shells may persist for many years in a subfossil condition (Cameron 2003), and as such they do not provide evidence that a species is still present at a site (Kerney 1999). Timing of survey work also becomes an issue if dead specimens are to be included. For example, Cameron (1982) reported that they recorded a larger than average number of dead shells at the end of winter, and also in September. In the Burren grasslands, O’Donovan (1987) found a much higher number of empty shells of Helicella itala (Linnaeus, 1758) in

2

September, compared to other times of the year. Thus the relative advantages and disadvantages of including immature and/or dead shells in any study must always be weighed up. With such a high proportion of these categories of individuals in the 0.5-1 mm size fraction, the relative value of processing these (even if the immature and dead specimens are not identified to species) must be considered. As well as the overall numbers of individual snail shells recorded, the identity of the species found in the small size fraction, and their abundance relative to the larger fraction, provides Irish Naturalists’ Journal Vol. 36 Part 1 5


valuable information in the investigation of optimal sieve mesh size. Only six species were recorded as adults in the small size fraction in this study (compared to 24 in the larger fraction), but nonetheless these data provided a number of important results: one species was completely new to the dataset; a median of two new species were added to the species list for each of the 12 study sites; and abundance data revealed gross under-estimations for some species. In the case of the current dataset, had we not included the data from the 0.5-1 mm size fraction, the widespread occurrence of the Red-listed (Byrne et al. 2009) ‘Vulnerable’ species, Acicula fusca, at the study sites would have gone completely unrecorded. Further, exceedingly abundant species such as Carychium tridentatum would have been recorded only in numbers less than ten. Clearly these findings have implications for molluscan survey work and the decisions scientists make when sampling. Other studies have also demonstrated that not including small, cryptic or taxonomically challenging organisms can have a large impact on assessments of diversity for a given area. For example, the work of Kelly (2000) demonstrated that different levels of resolution in floristic recording dramatically influenced the levels of diversity which were recorded from an area of woodland, and Kowalewski and Hoffmeister (2003) showed that the exclusion of smaller fossil molluscs due to the use of differing sieve mesh sizes can dramatically alter results. Kidwell (2002), working on live-dead comparison studies, also found a strong influence of sieve mesh size on the interpretation of both palaeoecological and ecological molluscan data. Another interesting aspect to emerge from this study was the difference in findings among habitats in proportions of species missed. Grasslands showed, on average, a 42 % increase in number of species when data from the small size fraction were included, compared to 17 % and 26 % for woodland and scrub respectively. This may indicate that a smaller mesh size is more appropriate in grassy/open habitats, but less necessary in woody/shaded ones. This raises the interesting possibility of using different sampling methods depending on the habitat type under study. Nekola (2005), in a large study involving over 400,000 specimens collected from over 800 sites spread across North America, found that very small species were most frequent in grasslands (rather than rock outcrop or forest). Data on size from Kerney and Cameron (1979) and Falkner et al. (2001) showed that the six species recorded from the 0.5-1 mm size fraction were among the smallest from the complete species list for this study. Only 6 Irish Naturalists’ Journal Vol. 36 Part 1


Acanthinula aculeata falls in their smallest size category but was not recorded in the small size fraction here. However, its height and breadth measurements reveal that it is the most globular of the small species, and thus its shape, as well as its size, is responsible for its not being recorded (at least as an adult) in the small size fraction in this study. One species, Acicula fusca, classed in the second smallest size category in the Falkner database, was recorded only in the small size fraction in this study. This is again accounted for by its shape: breadth measurements show that it is the most slender of the recorded snail species, making it likely to slip through even a narrow sieve mesh. This suggests that information on size and shape, which is readily available, can be used to predict which species may be missed or under-estimated if a larger sieve mesh size is used. Indeed, the detailed data available in the database of Falkner et al. (2001), including that on distribution, allows the production of lists of ‘expected’ species for given habitat types in given geographical areas. This, combined with the size and shape information, could be used to help determine the most appropriate mesh size to use, or, conversely, to help identify which species are likely to be missed or under-estimated in a particular survey. Acknowledgements Funding for this work came largely from the EPA (Environmental Protection Agency) as part of the BioChange project, with supplementary funding also received from NPWS (National Parks and Wildlife Service, thanks especially to the late Marie Dromey). A grant was received from SYNTHESYS (the European Unionfunded Integrated Activities Grant) to access the mollusc collections in the Royal Belgian Institute of Natural Sciences (RBINS). Fieldwork took place with the kind permission of landowners in Clare and Galway. Thanks to NUI Galway for the use of the Carran Research Station. Thanks to the volunteers who helped in the field and in the lab, and to Ian Killeen for identification advice. Helpful comments were received from colleagues Jenni Roche and Bettina Stefanini. Accepted 10 July 2017 References Anderson, R. (2005) An annotated list of the non-marine Mollusca of Britain and Ireland. Journal of Conchology 38: 607-637. Barba, B., Larranaga, A., Otermin, A. and Pozo, J. (2010) The effect of sieve mesh size on the description of macroinvertebrate

communities. Limnetica 29: 211-220. Byrne, A., Moorkens, E.A., Anderson, R., Killeen, I.J. and Regan, E.C. (2009) Ireland Red List No. 2 - Non-Marine Molluscs. National Parks and Wildlife Service, Department of the Environment, Heritage and Local Government, Dublin. Cameron, R.A.D. (1982) Life histories, density and biomass in a woodland snail community. Journal of Molluscan Studies 48: 159-166. Cameron, R.A.D. (2003) Keys for the identification of land snails in the British Isles. Field Studies Council, Shropshire, UK. Cameron, R.A.D. and Pokryszko, B.M. (2005) Estimating the species richness and composition of land mollusc communities: problems, consequences and practical advice. Journal of Conchology 38: 529-548. Cernohorsky, N.H., Horsak, M. and Cameron, R.A.D. (2010) Land snail species richness and abundance at small scales: the effects of distinguishing between live individuals and empty shells. Journal of Conchology 40: 233241. Chatfield, J.E. (1977) Non-marine Mollusca and Isopoda collected in Northern Ireland, Autumn 1975, with records of Limax grossui Lupu, a slug new to the Irish fauna. Irish Naturalists’ Journal 19: 66-69. Comber, M. and Jones, C. (2006) Assessment of landscape change and effects on archaeology and an assessment of habitat survey in the Burren, Co. Clare. The Heritage Council, Kilkenny. Cook, A. (2001) Behavioural ecology: on doing the right thing, in the right place at the right time. In: Barker, G.M. (ed.) The biology of terrestrial molluscs: 447-488. CABI Publishing, UK. Deenihan, A., Donlan, J., Breen, J. and Moles, R. (2009) Mid-term impacts of excluding large grazing animals on a Burren grass/scrubland patch. Biology and Environment: Proceedings of the Royal Irish Academy 109B: 107-113. Dunford, B. and Feehan, J. (2001) Agricultural practices and natural heritage: a case study of the Burren uplands, Co. Clare. Tearmann: Irish journal of agri-environmental research 1: 19-34. Falkner, G., Obrdlik, P., Castella, E. and Speight, M.C.D. (2001) Shelled Gastropoda of western Europe. Munchen: Friedrich-HeldGesellschaft. Ferraro, S.P., Cole, F.A., Deben, W.A. and Swartz, R.C. (1989) Power-Cost Efficiency of eight macrobenthic sampling schemes in Puget Sound, Washington, USA. Canadian Journal of Fisheries and Aquatic Sciences 46: 2157-2165. Gittenberger, E., Preece, R.C. and Ripken, T.E.J.

(2006) Balea heydeni Von Maltzan, 1881 (Pulmonata: Clausiliidae): an overlooked but widely distributed European species. Journal of Conchology 39: 145-150. James, R.J., Lincoln Smith, M.P. and Fairweather, P.G. (1995) Sieve mesh-size and taxonomic resolution needed to describe natural spatial variation of marine macrofauna. Marine Ecology Progress Series 118: 187-198. Kelly, D.L. (2000) Charting diversity in a Killarney oakwood: levels of resolution in floristic recording, and the effects of felling and fencing. In: Rushton, B.S. (ed.) Biodiversity: the Irish dimension: 76-93. Royal Irish Academy, Dublin. Kerney, M.P. (1999) Atlas of the land and freshwater molluscs of Britain and Ireland. Harley Books, Essex. England. Kerney, M.P. and Cameron, R.A.D. (1979) A field guide to the land snails of Britain and north-west Europe. Collins, London. Kidwell, S.M. (2002) Mesh-size effects on the ecological fidelity of death assemblages: a meta-analysis of molluscan live-dead studies. Geobios, Memoire special no. 24: 107-119. Kowalewski, M. and Hoffmeister, A.P. (2003) Sieves and fossils: effects of mesh size on paleontological patterns. Palaios 18: 460-469. Long, M.P. (2011) Plant and snail communities in three habitat types in a limestone landscape in the west of Ireland, and the effects of exclusion of large grazing animals. Unpublished PhD Thesis, Trinity College, University of Dublin. Menez, A. (2001) Assessment of land snail sampling efficacy in three Mediterranean habitat types. Journal of Conchology 37: 171176. Moorkens, E.A. (1999) An inventory of Mollusca in a selection of sites, with special reference to Vertigo angustior, V. geyeri and V. moulinsiana. A report for Dúchas, The Heritage Service, National Parks and Wildlife Service, Dublin. Moorkens, E.A. (2001) An inventory of Mollusca in potential SAC sites, with special reference to Vertigo species. A report for Dúchas, The Heritage Service, National Parks and Wildlife Service, Dublin. Moorkens, E.A. (2003) Final Baseline Report on Molluscan Surveys of Pollardstown Fen 19982003. A report for Kildare County Council. Moorkens, E.A. and Gaynor, K. (2002) Studies on Vertigo angustior at a coastal site in western Ireland (Gastropoda, Pulmonata: Vertiginidae). In: Speight, M.C.D., Moorkens, E.A. and Falkner, G. (eds) Proceedings of the workshop on conservation biology of European Vertigo species. Heldia 5: 125-134. Nekola, J.C. (2005) Geographic variation in richness and shell size of eastern North Irish Naturalists’ Journal Vol. 36 Part 1 7


valuable information in the investigation of optimal sieve mesh size. Only six species were recorded as adults in the small size fraction in this study (compared to 24 in the larger fraction), but nonetheless these data provided a number of important results: one species was completely new to the dataset; a median of two new species were added to the species list for each of the 12 study sites; and abundance data revealed gross under-estimations for some species. In the case of the current dataset, had we not included the data from the 0.5-1 mm size fraction, the widespread occurrence of the Red-listed (Byrne et al. 2009) ‘Vulnerable’ species, Acicula fusca, at the study sites would have gone completely unrecorded. Further, exceedingly abundant species such as Carychium tridentatum would have been recorded only in numbers less than ten. Clearly these findings have implications for molluscan survey work and the decisions scientists make when sampling. Other studies have also demonstrated that not including small, cryptic or taxonomically challenging organisms can have a large impact on assessments of diversity for a given area. For example, the work of Kelly (2000) demonstrated that different levels of resolution in floristic recording dramatically influenced the levels of diversity which were recorded from an area of woodland, and Kowalewski and Hoffmeister (2003) showed that the exclusion of smaller fossil molluscs due to the use of differing sieve mesh sizes can dramatically alter results. Kidwell (2002), working on live-dead comparison studies, also found a strong influence of sieve mesh size on the interpretation of both palaeoecological and ecological molluscan data. Another interesting aspect to emerge from this study was the difference in findings among habitats in proportions of species missed. Grasslands showed, on average, a 42 % increase in number of species when data from the small size fraction were included, compared to 17 % and 26 % for woodland and scrub respectively. This may indicate that a smaller mesh size is more appropriate in grassy/open habitats, but less necessary in woody/shaded ones. This raises the interesting possibility of using different sampling methods depending on the habitat type under study. Nekola (2005), in a large study involving over 400,000 specimens collected from over 800 sites spread across North America, found that very small species were most frequent in grasslands (rather than rock outcrop or forest). Data on size from Kerney and Cameron (1979) and Falkner et al. (2001) showed that the six species recorded from the 0.5-1 mm size fraction were among the smallest from the complete species list for this study. Only 6 Irish Naturalists’ Journal Vol. 36 Part 1


Acanthinula aculeata falls in their smallest size category but was not recorded in the small size fraction here. However, its height and breadth measurements reveal that it is the most globular of the small species, and thus its shape, as well as its size, is responsible for its not being recorded (at least as an adult) in the small size fraction in this study. One species, Acicula fusca, classed in the second smallest size category in the Falkner database, was recorded only in the small size fraction in this study. This is again accounted for by its shape: breadth measurements show that it is the most slender of the recorded snail species, making it likely to slip through even a narrow sieve mesh. This suggests that information on size and shape, which is readily available, can be used to predict which species may be missed or under-estimated if a larger sieve mesh size is used. Indeed, the detailed data available in the database of Falkner et al. (2001), including that on distribution, allows the production of lists of ‘expected’ species for given habitat types in given geographical areas. This, combined with the size and shape information, could be used to help determine the most appropriate mesh size to use, or, conversely, to help identify which species are likely to be missed or under-estimated in a particular survey. Acknowledgements Funding for this work came largely from the EPA (Environmental Protection Agency) as part of the BioChange project, with supplementary funding also received from NPWS (National Parks and Wildlife Service, thanks especially to the late Marie Dromey). A grant was received from SYNTHESYS (the European Unionfunded Integrated Activities Grant) to access the mollusc collections in the Royal Belgian Institute of Natural Sciences (RBINS). Fieldwork took place with the kind permission of landowners in Clare and Galway. Thanks to NUI Galway for the use of the Carran Research Station. Thanks to the volunteers who helped in the field and in the lab, and to Ian Killeen for identification advice. Helpful comments were received from colleagues Jenni Roche and Bettina Stefanini. Accepted 10 July 2017 References Anderson, R. (2005) An annotated list of the non-marine Mollusca of Britain and Ireland. Journal of Conchology 38: 607-637. Barba, B., Larranaga, A., Otermin, A. and Pozo, J. (2010) The effect of sieve mesh size on the description of macroinvertebrate

communities. Limnetica 29: 211-220. Byrne, A., Moorkens, E.A., Anderson, R., Killeen, I.J. and Regan, E.C. (2009) Ireland Red List No. 2 - Non-Marine Molluscs. National Parks and Wildlife Service, Department of the Environment, Heritage and Local Government, Dublin. Cameron, R.A.D. (1982) Life histories, density and biomass in a woodland snail community. Journal of Molluscan Studies 48: 159-166. Cameron, R.A.D. (2003) Keys for the identification of land snails in the British Isles. Field Studies Council, Shropshire, UK. Cameron, R.A.D. and Pokryszko, B.M. (2005) Estimating the species richness and composition of land mollusc communities: problems, consequences and practical advice. Journal of Conchology 38: 529-548. Cernohorsky, N.H., Horsak, M. and Cameron, R.A.D. (2010) Land snail species richness and abundance at small scales: the effects of distinguishing between live individuals and empty shells. Journal of Conchology 40: 233241. Chatfield, J.E. (1977) Non-marine Mollusca and Isopoda collected in Northern Ireland, Autumn 1975, with records of Limax grossui Lupu, a slug new to the Irish fauna. Irish Naturalists’ Journal 19: 66-69. Comber, M. and Jones, C. (2006) Assessment of landscape change and effects on archaeology and an assessment of habitat survey in the Burren, Co. Clare. The Heritage Council, Kilkenny. Cook, A. (2001) Behavioural ecology: on doing the right thing, in the right place at the right time. In: Barker, G.M. (ed.) The biology of terrestrial molluscs: 447-488. CABI Publishing, UK. Deenihan, A., Donlan, J., Breen, J. and Moles, R. (2009) Mid-term impacts of excluding large grazing animals on a Burren grass/scrubland patch. Biology and Environment: Proceedings of the Royal Irish Academy 109B: 107-113. Dunford, B. and Feehan, J. (2001) Agricultural practices and natural heritage: a case study of the Burren uplands, Co. Clare. Tearmann: Irish journal of agri-environmental research 1: 19-34. Falkner, G., Obrdlik, P., Castella, E. and Speight, M.C.D. (2001) Shelled Gastropoda of western Europe. Munchen: Friedrich-HeldGesellschaft. Ferraro, S.P., Cole, F.A., Deben, W.A. and Swartz, R.C. (1989) Power-Cost Efficiency of eight macrobenthic sampling schemes in Puget Sound, Washington, USA. Canadian Journal of Fisheries and Aquatic Sciences 46: 2157-2165. Gittenberger, E., Preece, R.C. and Ripken, T.E.J.

(2006) Balea heydeni Von Maltzan, 1881 (Pulmonata: Clausiliidae): an overlooked but widely distributed European species. Journal of Conchology 39: 145-150. James, R.J., Lincoln Smith, M.P. and Fairweather, P.G. (1995) Sieve mesh-size and taxonomic resolution needed to describe natural spatial variation of marine macrofauna. Marine Ecology Progress Series 118: 187-198. Kelly, D.L. (2000) Charting diversity in a Killarney oakwood: levels of resolution in floristic recording, and the effects of felling and fencing. In: Rushton, B.S. (ed.) Biodiversity: the Irish dimension: 76-93. Royal Irish Academy, Dublin. Kerney, M.P. (1999) Atlas of the land and freshwater molluscs of Britain and Ireland. Harley Books, Essex. England. Kerney, M.P. and Cameron, R.A.D. (1979) A field guide to the land snails of Britain and north-west Europe. Collins, London. Kidwell, S.M. (2002) Mesh-size effects on the ecological fidelity of death assemblages: a meta-analysis of molluscan live-dead studies. Geobios, Memoire special no. 24: 107-119. Kowalewski, M. and Hoffmeister, A.P. (2003) Sieves and fossils: effects of mesh size on paleontological patterns. Palaios 18: 460-469. Long, M.P. (2011) Plant and snail communities in three habitat types in a limestone landscape in the west of Ireland, and the effects of exclusion of large grazing animals. Unpublished PhD Thesis, Trinity College, University of Dublin. Menez, A. (2001) Assessment of land snail sampling efficacy in three Mediterranean habitat types. Journal of Conchology 37: 171176. Moorkens, E.A. (1999) An inventory of Mollusca in a selection of sites, with special reference to Vertigo angustior, V. geyeri and V. moulinsiana. A report for Dúchas, The Heritage Service, National Parks and Wildlife Service, Dublin. Moorkens, E.A. (2001) An inventory of Mollusca in potential SAC sites, with special reference to Vertigo species. A report for Dúchas, The Heritage Service, National Parks and Wildlife Service, Dublin. Moorkens, E.A. (2003) Final Baseline Report on Molluscan Surveys of Pollardstown Fen 19982003. A report for Kildare County Council. Moorkens, E.A. and Gaynor, K. (2002) Studies on Vertigo angustior at a coastal site in western Ireland (Gastropoda, Pulmonata: Vertiginidae). In: Speight, M.C.D., Moorkens, E.A. and Falkner, G. (eds) Proceedings of the workshop on conservation biology of European Vertigo species. Heldia 5: 125-134. Nekola, J.C. (2005) Geographic variation in richness and shell size of eastern North Irish Naturalists’ Journal Vol. 36 Part 1 7


American land snail communities. Records of the Western Australian Museum Supplement 68: 39-51. O’Donovan, G. (1987) An ecosystem study of grasslands in the Burren National Park, Co. Clare. Unpublished PhD Thesis, University of Dublin. O’Donovan, G. (2001) Productivity, grazing pressure and phenology of a Sesleria-dominated grassland in the Burren National Park. Tearmann: Irish journal of agri-environmental research 1: 35-54. Oggier, P., Zschokke, S. and Baur, B. (1998) A comparison of three methods for assessing the gastropod community in dry grasslands. Pedobiologia 42: 348-357. Osborne, B. and Jeffrey, D.W. (2003) Introduction

and overview - understanding the Burren. Biology and Environment: Proceedings of the Royal Irish Academy 103B: 107-109. Platts, E., Bailey, S., McGrath, D. and McGeough, G. (2003) A survey of the land winkle Pomatias elegans (Müller, 1774) in the Burren, Co. Clare. Biology and Environment: Proceedings of the Royal Irish Academy 103B: 197-201. Viney, M. (2003) Ireland. Smithsonian Institution, USA and Blackstaff Press Limited, Belfast, Northern Ireland. Webb, D.A. and Scannell, M.J.P. (1983) Flora of Connemara and the Burren. Royal Dublin Society, Dublin and Cambridge University Press, Cambridge.

Bait preference in Irish small rodents Claire Bealin and *Colin Lawton Zoology, School of Natural Sciences, Ryan Institute, National University of Ireland, Galway Wood Mice and Bank Voles were captured in two urban woodlands in Galway city using Longworth traps baited with one of three different baits. Wood Mice showed a preference for peanuts, while Bank Voles were more likely to be captured in traps baited with a commercial hamster pet food. Different bait preferences were also shown by male and female Wood Mice, with males more likely to choose peanuts. Keywords: Small mammal, bait preference, peanuts, oats, pet food Introduction Terrestrial small mammals are often abundant within a habitat, but generally difficult to observe and track given their size and behaviour (Hoffman et al. 2010). As such, surveying these taxa is largely carried out using trapping methods. Many small mammal population studies include the use of live capture traps as a means of determining population density and other population dynamics (Smith et al. 1975, Krebs 1989, Hoffman et al. 2010). However, it is recognised in ecology that using such techniques for population density is potentially affected by a trapping bias (e.g. Hancock and Legg 2012). The accuracy and efficacy of trapping surveys is dependent on the technique chosen (Thompson et al. 2005). There are several factors that can affect the individual’s response to a trap, which in turn can affect the estimates of true population size and the overall success of the study. For example, trap location (e.g. ground vs tree canopy), season and sampling effort. The type of trap and bait used are important variables in capture diversity and success (Beer 1964, Pizzimenti 1979, Hice and Velazco 2013). However, the choice of bait in rodent and other small mammal surveys often depends on the preference of the researcher rather than empirical data (e.g. Hoffman et al. 2010). Logistics can also play a part. For example, some baits may be deemed unsuitable during damp weather conditions, or can be too much of a mess in the traps. It is generally recognised that certain bait types are required for broad cohorts of mammals (insects such as meal worms for shrews; meat for carnivores; peanuts for rodents), but not whether species specific preferences are influencing results. As live trapping is often used to determine relative species abundances in rodents, it is important to consider the sensitivity of a species to a given bait. Bait preference has *Corresponding author – [email protected]

8 Irish Naturalists’ Journal Vol. 36 Part 1

been shown to occur at species level in rodents (Beer 1964, Fitch 1954, Rickart et al. 1991). Furthermore, rodents have shown an ability to distinguish baits based on nutritional cues and alter preferences through experience (Partridge and Maclean 1981). Achieving unbiased estimations of small mammal species composition and population densities using trapping methods is a knowledge gap that researchers must strive to close. To date, a comprehensive list matching each species to the most agreeable bait has yet to be established. This study sought to investigate whether explicit bait preferences exist in wild rodents. In Ireland, rodent studies using Longworth traps usually focus on two species, the Wood Mouse (Apodemus sylvaticus Linnaeus, 1758) and, within a more restricted range, the more recently introduced Bank Vole (Myodes glareolus (Schreber, 1780)). Sometimes studies may be specifically aimed at finding one species in particular, in which case the optimum bait for that species should be used. Alternatively, some studies are investigating the small mammal community, and it is critical that a bait that is more likely to attract one species over another is avoided. In this study we investigated Wood Mouse and Bank Vole populations in two urban woodland habitats in Galway city, Ireland. Three different baits were used, to see if a preference was shown by either species for a bait type, or if there was a preference shown by cohorts (e.g. by sex) within a species. Methods and materials The study was conducted at two locations within Galway city: Terryland Forest Park (M 298 262) and Unclin wood (M 339 253) in the autumn and winter of 2015/2016. Both are classified as semi-natural woodland habitats as per the Heritage Council classification (Fossitt 2000) and Irish Naturalists’ Journal Vol. 36 Part 1 9