J. Ky. Acad. Sci. 77(1–2):44–51. 2016.
Nest Site Selection and Nest Depredation of Carolina Chickadees Danielle M. Frevola1 and Lindsey A. Walters Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099
ABSTRACT Nest location is an important factor that influences nestlings’ success. Poor nest location could lead to exposure to predators and to a lack of nearby resources. We examined nest site selection and nest depredation of Carolina chickadees (Poecile carolinensis) from 2011–2015 at a field site with artificial nest boxes. In this cavity-nesting species, both members of a breeding pair inspect multiple cavities before deciding on a location to build a nest. We examined whether Carolina chickadee nest location preference and predation rates were related to factors such as proximity to the forest edge, a water source, neighboring cavities, and buildings, as well as the forest type the nest was located in. We found that Carolina chickadee nests that were closer to the forest edge were depredated more often; however, despite this increased risk of nest loss near the forest edge, the chickadees did not prefer boxes located away from the edge. The other factors that we measured were not related to nest box occupancy or predation risk. Future research should focus on why these birds continue to nest in more dangerous edge locations and on what other factors affect their nest selection decisions.
INTRODUCTION Selecting and building a nest is a time and energy consuming investment for many cavity nesting bird species (Withers 1977; Nilsson and Råberg 2001). Nest location can be a vital factor contributing to nestlings’ success. An optimal nest location will provide both the offspring and the parents with ample amounts of resources as well as protection against predators (Albano 1992; Danchin and Wagner 1997). Though nest location contributes strongly to the fitness of nestlings, research into what factors lead to greater fitness as a result of nest location has not produced definite results. For example, within the genus Poecile there are conflicting results about how nest height, entrance hole height, and surrounding tree species composition can influence nest selection (Brewer 1961; Christman and Dhondt 1997; Mahon and Martin 2006). Even more complex is determining if a species can achieve greater fitness by nesting along the forest edge or within the interior forest. The forest edge is frequently viewed as preferred habitat because it offers different vegetation zones and the availability of more than one landscape. In some species, nesting along the habitat edge provides diverse resources because of this unique landscape and can lead to greater success (Dobkin et al. 1995; 1
Aitken and Martin 2004). For example, in the great tit (Parus major), reproductive success is greater along forest edges than interior habitats because of better foraging habitat (Wilkin et al. 2007). Conversely, habitat along the edge can also be more sensitive to environmental changes, which can lead to species favoring the interior forest (Watson et al. 2004). Furthermore, habitat in the interior forest can provide greater tree species richness, consequently supporting abundant resources and potentially producing less competition (Oliveira et al. 2004). In species such as the yellow-rumped flycatcher (Ficedula zanthopygia) and the tree swallow (Tachycineta bicolor), nest success increased with distance from the forest edge as a result of lower competition (Deng and Gao 2005; Rendell and Robertson 1990). The risk of depredation is another influential component of nest location (Fontaine and Martin 2006). Often, predation is the primary cause of nest mortality for birds (Nilsson 1984; Albano 1992; Lima 2009; Wesołowski ´ 2012). Snake depredation is comand Rowinski mon among small passerines and is directly related to proximity to forest edge, where the risk of predation is greater for cavity nests ¨ 1991; located closer to the edge (Sandstrom Weatherhead and Blouin-Demers 2004; Fisher and Wiebe 2006). As ectothermic predators, snake predation is more likely to occur along the forest edge because the thin canopy cover increases the ground temperature and allows
Corresponding author email:
[email protected]
44
Nest Site Location and Predation—Frevola and Walters snakes to forage efficiently. Some bird species have demonstrated the ability to increase their nesting success by evaluating and responding to the risk of predation (Lima 2009). For example, female common goldeneyes (Bucephala clangula) whose nests are depredated are more likely to choose new cavities the following year compared to females that do not experience nest mortality (Dow and Fredga 1985). Other cavity nesting birds tend to select cavities that have low risk of predation characteristics associated with them, such as cavities that are high off of the ground and that are relatively isolated (Cockle et al. 2011). For this study, we examined nest site selection by Carolina chickadees (Poecile carolinensis), a cavity nesting songbird commonly found throughout the southeastern United States. In Carolina chickadees, the male and female will inspect and occasionally build nests in multiple cavities before committing to one cavity (Brewer 1961; Mostrom et al. 2002). Because more than one cavity is inspected, it is assumed that there are variables influencing nest location selection; i.e., the pair is not simply choosing the first cavity that they find. The breeding biology of this species is not well studied, and previous research has produced inconclusive results about what habitat qualities are most preferred. Specifically, edge habitat can provide risky conditions for breeding Carolina chickadee pairs to be successful (Albano 1992; Doherty and Grubb Jr. 2002), but previous studies provide conflicting evidence about whether or not this species prefers interior forest habitats or edges (Kroodsma 1984; McIntyre 1995). The goals of this study were to determine what habitat characteristics influence nest location preference and whether predation covaries with these characteristics. We predicted that: 1) Cavities that were located closer to the forest edge would be occupied less frequently because the risk of snake predation at these boxes would be greater compared to boxes in the interior forest. 2) Boxes that were located closer in proximity to another box would be occupied less often. Once a nesting territory is established, the immediate resources available for the parents to support fledglings can become limiting and competition for the resources can decrease nesting success nearby (Muller et al. 1997). 3) Because different forest types could
45
provide different amounts of protection and resources, we expected Carolina chickadees to occupy boxes in certain forest types preferentially. There were six different forest types present at the study site: old field, young post agriculture field, over mature beech forest, over mature mesic hardwood, cedar woodland, and mesic mature forest. Carolina chickadees are historically most commonly recorded in mesic hardwood forests (Brewer 1963); consequently, we expected that chickadees would prefer nest boxes in over mature mesic hardwood forest instead of the other five forest categories present. 4) Because streams support insect diversity, which provides a valuable food source for Carolina chickadees throughout the summer (Lucas and Walter 1991), we expected cavities located close to a stream to be occupied more frequently than cavities at a greater distance from this source. 5) Finally, we predicted that cavities that are located closer to buildings would be less desirable due to the human interaction and potential for nest disturbance. MATERIALS AND METHODS We collected data for this study at St. Anne Woods and Wetlands in Melbourne, Kentucky (Figure 1). Thirty-eight artificial nest boxes were distributed among forested areas and along forest edge. The wooden nest boxes had the dimensions 10 cm deep × 8.3 cm wide with an entrance hole that was 2.8 cm in diameter. The boxes had a sloped roof with a height of 23.6 cm in the front and 28.0 cm in the back. The average box height from the ground to the top of the box was 167.19 ± 7.83 SD cm. All boxes were mounted on metal poles. We collected data for this study over five breeding seasons from 2011–2015, in which we observed 38 nesting attempts in 22 different cavities. Sixteen of the nest boxes were never used during this time. Carolina chickadees used the nest boxes from early April through early June. We checked nest boxes every other day once the breeding season began to note if any new nests had formed and which nests, if any, had been depredated. During the 38 nesting attempts, 13 nests were depredated and 25 were not. The presumed predator, a black rat snake (Pantherophis obsoletus), was discovered inside of the nest box for two of the 13 predation incidents.
46
Journal of the Kentucky Academy of Science 77(1–2)
Figure 1. Field site map created using Geospatial Information System (GIS) ArcGIS 10.2. Circles represent the location of edge nest boxes and triangles represent the location of interior nest boxes.
Nest Site Location and Predation—Frevola and Walters
47
Table 1. Results of the likelihood ratio test (LRT) to determine which explanatory variables should be kept in the generalized linear model predicting nest box occupancy. No explanatory variables significantly improved on the null model. Explanatory variable
Distance to forest edge Distance to nearest box Distance to stream Distance to human disturbance Forest type
We collected geographic coordinates of the nest boxes for spatial analysis in Geographic Information System (GIS) by using a GPS unit (Timble GeoExplorer 2008 Series GeoXT). In ArcGIS 10.2, we determined the distance from each nest box to neighboring boxes, streams, forest edge, and buildings by using the measuring tool. In addition, in ArcGIS, we identified the forest type each nest box was located in by using a previously produced map (L. Brewer, Northern Kentucky University, pers. comm., 25 Jan 2016) that illustrated the different forest types that were present in our field site. We then statistically analyzed these data using multiple logistic regression. We used the program R (R Core Team 2014) to run generalized linear models using the glm function with a binomial family and logit link (Dalgaard 2002). To analyze occupancy preference, the response variable was whether or not a nest box had ever been occupied and to analyze predation risk, the response variable was whether or not an occupied nest box experienced depredation. For both models, the initial explanatory variables were the distance to the forest edge, distance to the closest neighboring box, distance to a stream, distance to buildings, and forest type. We used the drop1 command in R to conduct likelihood ratio tests to determine which explanatory variables should be kept in the final models. RESULTS Our geospatial analysis of the occupancy data found that none of our measured habitat variables predicted whether or not a nest box would be occupied. The likelihood ratio test showed that none of the explanatory variables provided a better fit than the null model (Table 1). In particular, occupied nest boxes were not signif-
LRT test statistic (χ2)
0.373 0.052 0.710 0.154 0.201
P-value
0.541 0.820 0.400 0.695 0.650
icantly farther from the forest edge than nonoccupied nest boxes (Figure 2). For the predation analysis, the likelihood ratio tests indicated that only distance to the edge and distance to the stream should be kept in our final model (Table 2), so we removed the other explanatory variables and ran the generalized linear model again using only those two as explanatory variables. In this reduced model, distance to the forest edge significantly predicted whether or not a nest box would be depredated (z = −2.003, P = 0.045). Nest boxes that suffered depredation were located closer to the forest edge than those that did not (Figure 3). Distance to the stream did not significantly predict predation status (z = 0.288, P = 0.773). DISCUSSION We found that Carolina chickadees did not have a significant preference between using nest boxes along the forest edge versus the interior forest, which contradicts some findings classifying the species as an interior species
Figure 2. Mean distance (in meters) ± SE to the forest edge of nest boxes that were or were not occupied by breeding Carolina chickadees. Distance to edge did not predict occupancy.
48
Journal of the Kentucky Academy of Science 77(1–2)
Table 2. Results of the likelihood ratio test (LRT) to determine which explanatory variables should be kept in the generalized linear model predicting nest box depredation. Distance to forest edge and distance to stream significantly improved the null model and were retained in the final model. Explanatory variable
Distance to forest edge Distance to nearest box Distance to stream Distance to human disturbance Forest type
(McIntyre 1995) or a species favoring the edge (Kroodsma 1984). Despite this lack of preference, we found that nest boxes that suffered depredation were significantly closer to the forest edge. A possible explanation for Carolina chickadees to repeatedly occupy boxes along the edge, despite the higher predation risk, could be a trade-off between this risk and energy expended on incubation. Cavities located along the forest edge potentially have greater mean temperatures than interior boxes due to less canopy cover, and therefore more sun exposure (Wiebe 2001). A consequence of greater temperatures is the female chickadees could spend less time incubating eggs and brooding nestlings, and therefore will have more energy to allocate towards foraging (Webb and King 1983). If the nestlings survive to fledge, those nests located along the forest edge may have greater fitness because they received more provisions than nests located in the interior forest (Schwagmeyer and Mock 2008). In addition, if the female is able to conserve energy during incubation it is possible that she is able to
Figure 3. Mean distance (in meters) ± SE to the forest edge of nest boxes that did or did not experience nest predation. Depredated nest boxes were located significantly closer to the forest edge.
LRT test statistic (χ2)
4.212 1.623 3.948 1.373 0.002
P-value
0.040 0.202 0.047 0.241 0.962
prolong her life and continue to breed for additional years, compared to females that brood in the interior forest (Winkler and Wallin 1987; Reid et al. 2000). Future studies should explore the idea of temperature and incubation patterns of occupied boxes along the forest edge compared to the interior forest, as well as the fitness of fledglings from both location types. None of the other factors that we examined, such as forest type, proximity to buildings, streams, and other cavities, differed between occupied and unoccupied boxes. One possibility that could explain this apparent lack of preference is that a location does not have enough high-quality nest sites available, so that both preferred and less desirable sites are being used. Boxes that are more optimal are being occupied first, and when density of occupied nests increases, less ideal boxes become ´ 1965). However, this seems occupied (Hilden unlikely in our population because many nest boxes go unused each year and distance to other cavities was not different between occupied and unoccupied boxes. If the chickadees were influenced by density, we would expect distance to other cavities to be a significant factor influencing cavity occupancy. Carolina chickadees are opportunistic feeders, feeding on both insects and seeds but preferring insects when the option is available (Mostrom et al. 2002). One explanation for why distance to a stream was not a significant factor in predicting cavity occupancy is that a high abundance of insects could be present throughout the habitat. Desirable food resources available throughout the area would decrease the importance of making a nest located near the stream in order to forage efficiently. In addition, home ranges for Carolina chickadees can reach up to 35 acres (Nice 1933; Brewer 1961), so any bird nesting in our study site would have
Nest Site Location and Predation—Frevola and Walters a stream within its home range. Future studies should investigate insect abundance throughout the study site to determine if food sources are equally distributed in the habitat. The fact that nest site preference did not seem to be affected by distance to buildings is not surprising for this species. Carolina chickadees are commonly found in urbanized areas (Atchison and Rodewald 2006), meaning chickadees are accustomed to human interaction and buildings. Furthermore, at our study site all major buildings were at least 50 m from cavities. It is reasonable to believe that because chickadees are familiar with human disturbance and because the buildings on the property are relatively far from cavities, human disturbance was not influential in cavity occupancy. While we did find different forest types at the field site, it is likely that all types were suitable habitat for Carolina chickadees. Carolina chickadees prefer trees that have harder wood when utilizing natural cavities because trees with thicker wood could lower the risk of predation (Martin et al. 2004). However, because we observed occupancy of artificial cavities, it is reasonable that forest type was not significant in determining preferred cavity location. It is likely that all forest types available provided sufficient shelter and food resources to adequately support nesting habitat and therefore, chickadees were not reliant on forest type when determining a nesting location. In conclusion, we have found that Carolina chickadees have no preference between nesting along the forest edge or the forest interior, despite there being a greater risk of predation to nests on the forest edge. There are many possibilities for why Carolina chickadees continue to nest along the forest edge, such as a tradeoff between nestling survival and fledgling fitness. We also determined that the presence of a neighboring cavity is not related to cavity occupancy, nor is distance to buildings and streams. Depredation is also not related to these variables. Additional research is needed to investigate success of fledglings that are incubated at the forest edge and the interior forest. Furthermore, studies exploring preferences in nesting location should continue in order to determine the most optimal location for Carolina chickadee nesting success. This study adds valuable information to the deficit in knowledge about Carolina chickadee
49
nest habitat preference and also highlights the need for further research, since many studies seem to have conflicting results about chickadee habitat preference. Furthermore, the results contribute to the scientific understanding of factors that influence the breeding success of cavity nesting birds; specifically, this study highlights how birds might choose to nest in unsafe habitats. This information can be used by scientists studying cavity nesting birds and by those trying to conserve imperiled species to provide cavities in the best location for the birds’ success. ACKNOWLEDGMENTS We would like to thank St. Anne Convent, the Schmits family, St. Anne Woods and Wetlands, and the Campbell County Conservation District for allowing us to use their property throughout this research. Northern Kentucky University’s Center for Integrative Natural Science and Mathematics (CINSAM) provided funding for this project and D. M. F. was supported by a Greaves Undergraduate Summer Research Fellowship. We also want to thank the Northern Kentucky University Center for Environmental Restoration, Victor Vanover, and Lawrence Brewer for providing additional support and supplies. Additionally, Brendan Hall, Ashley Haws, Zachary Holtkamp, Brittney Jones, Michelle Kelley, Spyncer Mones, Paige Moore, Shelby Nemec, Elizabeth Nickell, Allison Rigger, Cassie Volker, and Jaclyn Webber aided in field data collection. LITERATURE CITED Albano, D. J. 1992. Nesting mortality of Carolina Chickadees breeding in natural cavities. Condor 94: 371–382. Aitken, K. E., and Martin, K. 2004. Nest cavity availability and selection in aspen conifer groves in a grassland landscape. Canadian Journal of Forest Research 34: 2099– 2109. Andren, H., and P. Anglestam. 1988. Elevated predation rates as an edge effect in habitat islands: experimental evidence. Ecology 69: 544–547 Atchison, K. A., and A. D. Rodewald. 2006. The value of urban forests to wintering birds. Natural Areas Journal 26: 280–288. Benson, T. J., S. J. Chiavacci, and M. P. Ward. 2013. Patch size and edge proximity are useful predictors of brood parasitism but not nest survival of grassland birds. Ecological Applications 23: 879–887.
50
Journal of the Kentucky Academy of Science 77(1–2)
Brewer, R. 1961. Comparative notes on the life history of the Carolina Chickadee. The Wilson Bulletin 73: 348– 373. Brewer, R. 1963. Ecological and reproductive relationships of Black-capped and Carolina chickadees. The Auk 80: 9–47. Christman, B. J., and A. A. Dhondt. 1997. Nest predation in Black-capped Chickadees: How safe are cavity nests? The Auk 114: 769–773. Cockle, K., K. Martin, and K. Wiebe. 2011. Selection of nest trees by cavity-nesting birds in the Neotropical Atlantic forest. Biotropica 43: 228–236. Dalgaard, P. 2014. Logistic regression. In Introductory Statistics with R (pp. 191–209). Springer, New York. Danchin, E., and R. H. Wagner. 1997. The evolution of coloniality: the emergence of new perspectives. Trends in Ecology and Evolution 12: 342–347. Deng, W.H., and W. Gao. 2005. Edge effects on nesting success of cavity-nesting birds in fragmented forests. Biological Conservation 126: 363–370. Dobkin, D. S., Rich, A. C., Pretare, J. A., and W.H Pyle. 1995. Nest-site relationships among cavity-nesting birds of riparian and snowpocket aspen woodlands in the northwestern Great Basin. The Condor 97: 694–707. Doherty Jr, P. F., and T. C. Grubb Jr. 2002. Nest usurpation is an ‘edge effect’ for Carolina Chickadees Poecile carolinensis. Journal of Avian Biology 33: 77–82. Dow, H. and S. Fredga. 1985. Selection of nest sites by a hole-nesting duck, the goldeneye Bucephala clangula. Ibis 127: 16–30. Fisher, R. J., and K.L. Wiebe 2006. Nest site attributes and temporal patterns of northern flicker nest loss: effects of predation and competition. Oecologia, 147: 744–753. Fontaine, J. J., and T.E. Martin. 2006. Parent birds assess nest predation risk and adjust their reproductive strategies. Ecology Letters 9: 428–434. ´ O. 1965. Habitat selection in birds: a review. AnHilden, nales Zoologici Fennici 2: 53–75. Kroodsma, R. L. 1984. Effect of edge on breeding forest bird species. The Wilson Bulletin 96: 426–436. Lima, S. L. 2009. Predators and the breeding bird: behavioral and reproductive flexibility under the risk of predation. Biological Reviews 84: 485–513. Lucas, J. R. and L.R Walter. 1991 When should chickadees hoard food? Theory and experimental results. Animal Behaviour 41: 579–601. Mahon, C. L., and K. Martin. 2006. Nest survival of chickadees in managed forests: habitat, predator, and year effects. Journal of Wildlife Management 70: 1257– 1265. Martin, K., K. E. H. Aitken, and K. L. Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. The Condor 106: 5–19. McIntyre, N. E. 1995. Effects of forest patch size on avian diversity. Landscape Ecology 10: 95–99. Mostrom, A. M., Curry, R. L., and B. Lohr. 2002. The birds of North America: vol. 636. Carolina chickadee
(Poecile carolinensis) (A. Poole & F. Gill, Eds.). Philadelphia and Washington, DC: Academy of Natural Sciences and American Ornithologists’ Union. Muller, K. L., J. A. Stamps, V. V.Krishnan, and N. H. Willits. 1997. The effects of conspecific attraction and habitat quality on habitat selection in territorial birds (Troglodytes aedon). The American Naturalist 150: 650– 661. Nice, M. M. 1933. Robins and Carolina chickadees remating. Bird-banding 157. Nilsson, J. Å., and L. Råberg. 2001. The resting metabolic cost of egg laying and nestling feeding in great tits. Oecologia 128: 187–192. Nilsson, S. 1984. The evolution of nest-site selection among hole-nesting birds: the importance of nest predation and competition. Ornis Scandinavica 15: 167–175. Oliveira, M. A., A. S. Grillo, and M. Tabarelli. 2004. Forest edge in the Brazilian Atlantic forest: drastic changes in tree species assemblages. Oryx 38: 389–394. ¨ Sandstrom, U. 1991. Enhanced predation rates on cavity bird nests at deciduous forest edges: an experimental study. Ornis Fennica 68: 93–98. Schwagmeyer, P. L., and D.W. Mock. 2008. Parental provisioning and offspring fitness: size matters. Animal Behaviour, 75: 291–298. R Core Team. 2014. R: a language and environment for statistical computing. Version 3.1.1. R Foundation for Statistical Computing, Vienna, Austria. https://www.Rproject.org Reid, J. M., Monaghan, P., and G.D. Ruxton. 2000. Resource allocation between reproductive phases: the importance of thermal conditions in determining the cost of incubation. Proceedings of the Royal Society of London B: Biological Sciences 267: 37–41. Rendell, W. B., and R.J Robertson. 1990. Influence of forest edge on nest-site selection by Tree Swallows. The Wilson Bulletin 102: 634–644. Watson, J. E. M., R. J. Whittaker, and T. P. Dawson. 2004. Habitat structure and proximity to forest edge affect the abundance and distribution of forest-dependent birds in tropical coastal forests of southeastern Madagascar. Biological Conservation 120: 311–327. Webb, D. R., and J.R. King. 1983. An analysis of the heat budgets of the eggs and nest of the white-crowned sparrow, Zonotrichia leucophrys, in relation to parental attentiveness. Physiological Zoology 56: 493–505. ´ Wesołowski, T., and P. Rowinski. 2012. The breeding performance of Blue Tits Cyanistes caeruleus in relation to the attributes of natural holes in a primeval forest. Bird Study 59: 437–448. Weatherhead, P. J., and G. Blouin-Demers. 2004. Understanding avian nest predation: why ornithologists should study snakes. Journal of Avian Biology 35: 185– 190. Wiebe, K. L. 2001. Microclimate of tree cavity nests: is it important for reproductive success in northern flickers? The Auk 118: 412–421. Wilkin, T. A., Garant, D., Gosler, A. G., and B.C Shel-
Nest Site Location and Predation—Frevola and Walters don. 2007. Edge effects in the great tit: analyses of longterm data with GIS techniques. Conservation Biology 21: 1207–1217. Winkler, D. W., and K. Wallin. 1987. Offspring size and number: a life history model linking effort per off-
51
spring and total effort. The American Naturalist 129:708– 720. Withers, P.C, 1977. Energetic aspects of reproduction by the Cliff Swallow. The Auk 94: 718– 725.
