Feeding habits of the black kite Milvus migrans, red

ACTA ORNITHOLOGICA Vol. 34 (1999) N o. 1

Dorota Z a w a d z k a

Feeding habits of the Black Kite Milvus migrans, Red Kite Milvus milvus, White-tailed Eagle Haliaeetus albicilla and Lesser Spotted Eagle Aquila pomańna in Wigry National Park (NE Poland) Zawadzka D. 1999. Feeding habits of the Black Kite M ilvus migrans, Red Kite M ilvus milvus, W hite-tailed Eagle Haliaeetus albicilla and Lesser Spotted Eagle Aquila pomarina in Wigry Natonal Park (NE Poland). Acta om. 34:65-75. Abstract The study was conducted in the years 1989-1993. The Black Kite fed primarily on birds and fish, Red Kite — on birds, mammals and carrion. The White-tailed Eagle preyed almost exclusively on birds and fish, and the Lesser Spotted Eagle on small mammals, birds and frogs. The White-tailed Eagle was the most specialized species. Its food niche breadth was smallest among the studied species and food taken in water habitats accounted for 95% of its diet. The Black Kite had the widest food spectrum in terms of the frequency of prey while the Red Kite — in terms of the biomass consumed. The mean body mass of prey specimens taken by the White-tailed Eagle was 578 g, by the Red Kite — 235 g, the Black Kite — 230 g, andtheLesser Spotted Eagle — 34 g. The food niches of both Kites and the White-tailed Eagle strongly overlapped. The smallest overlap was between the food niches of the two Eagles and between the Lesser Spotted Eagle and the Black Kite. Key words: Diet composition, food niche, birds of prey, Wigry National Park 25 Czerwca 68 b /1 5 ,26-600 Radom, POLAND Received — Jan. 1999, accepted — June 1999

INTRODUCTION In Poland, the Black Kite Milvus migrans, Red Kite Milvus milvus, White-tailed Eagle Haliaeetus albicilla and Lesser Spotted Eagle Aquila pomańna are not num erous species, with the num ber of pairs from 400 of the Kites and W hite-tailed Eagle to about 1700 of the Lesser Spotted Eagle (unpubl. data of Komitet Ochrony Orłów 1998). These birds nest in forests near w ater and wet lands. Except the Lesser Spotted Eagle, they reach low densities (Komitet Ochrony Orłów 1995). The diet composition of the Kites, W hite-tailed Eagle and Lesser Spot-ted Eagle in Europe is know n fairly well (Palasthy & M eyburg 1973, C ram p & Simmons 1980, Fisher 1984, Gensbol & Thiede 1986, Ortlieb 1989, Veiga & Hiraldo 1990). However, there are only few data from Poland (M rugasiewicz 1984, Wacławek et al. 1998, Mizera

1999). A detailed study of m utual trophic relationships in the bird of prey com m unity was conducted only in Białowieża Primeval Forest (Jędrzejewska & Jędrze jewski 1998). The purpose of this study was to determ ine the diet composition and the degree of food competition of the Black Kite, Red Kite, W hite-tailed Eagle and Lesser Spotted Eagle in Wigry National Park.

STUDY AREA Wigry National Park (= WNP, 53°58’-54°10'N, 23°00'-23o15'E; 151 km 2), situated in the SuwałkiAugustów Lakeland, includes northern part of Augus tów Forest and the Wigry Lake. Forests cover 63% of the Park area, lakes — 19% and farm land — 15%. For-

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D. Z aw adzka

1984, Busse 1990). So one meal of carrion was equiva lent to 90 g in the Black Kite, 100 g in the Red Kite, and 500 g in the White-tailed Eagle. The food niche breadth (B) w as calculated accord ing to Levins (1968): В = 1 /Ър], where ^ is a fraction of each prey group (mammals, birds, fish, carrion, am phibians, insects) in the total biom ass or the num ber of prey items consumed. W ith six groups of prey taken for calculations, index В w ould vary from 1 (the nar MATERIAL AND METHODS rowest niche) to 6 (the broadest niche possible). The index of food niche overlap between the two species In the winter and spring, the nests of birds of prey was calculated after Pianka (1973): a. = І(р и x p j x were searched in old tree stands of the Park. All the nests [(XpJ) x [(Ір.2)Г,/2 w here œ is the overlap between of birds of prey and Raven Corvus corax, known from predators i and j, pa is the fraction of flth prey in the previous years had been checked. Sites of observation of total biomass consum ed by ith predator, is the frac the studied species were m arked on a map. In the years tion of the ath prey in the total biomass consumed by 1989-1993, 15-25 days were spent on searching for oc the ;th predator. Index a varies from 0 (exclusive food cupied nests each year. In the years 1994-1998, only a niches) to 1 (identical niches). breeding site of the White-tailed Eagle was checked. The G-test for the hom ogeneity of percentages was Pellets and prey rem ains were collected from nests used to analyse the frequency distribution of prey and nearby areas beneath during 2-7 breeding seasons grouped in classes of body mass. The assum ed null (Table 1) from A pril through July. Diet composition hypothesis was of 1:1:1 (Sokal & Rohlf 1981). was estim ated quantitatively by identifying eaten prey During the study, the habitat selectivity was Table 1. Study data on four raptor species investigated in Wigry National Park (NE Poland). Mmg — Milvus migrans, M m l — Milvus milvus, H al — Haliaeetus albicilla, Acjp — Aquila pomanna. estimated based on the observation of preying Raptor species Parameter birds. The way and Hal Mmg Mml M p ........ place of preying and — 1989-92 1991-98 1990-91 1989-93 Period 4 6 8 2 N studied broods if possible — the kind of 139 114 174 24 N pellets food eaten was deter 272 297 191 51 N prey specimens in pellets mined. The distance of 21 108 54 234 N prey remains 299 293 the feeding ground from 531 105 Total number of prey specimens 10.0 172.2 111.1 22.0 Total biomass of prey consumed (kg) the nest was noted. Thirty-five observations of the Black Kite, 103 of the Red Kite, 27 of the White items from the found rem ains (feathers, hair, skeletons, tailed Eagle and 42 of the Lesser Spotted Eagle were scales etc.). In the case of rem ains found in both pellets recorded. Another m ethod to estimate the habitat selec and food remains, double counting of prey items was tivity was based on the analysis of the degree of utiliza avoided by assum ing the lowest probable num ber of tion of a given habitat from the percent share of the food individuals eaten. The biomass of consumed food was taken there. All raptors prey was divided into species com puted by m ultiplying the num ber of prey items by taken from open areas, from forest and from water their body mass. The m ean mass of m ammals were habitats. The Mole Talpa europaea, Brown Hare Lepus taken from Goszczyński (1974), and the m ean mass of europaeus, Common Rat Rattus norvegicus, domestic hen, birds from Busse (1990). The mass of fish were calcu Partridge Perdix perdix, pigeons Columba spp., Sky Lark lated from the sizes of scales and parts of skeletons. The Alauda arvensis, corvids (but without Jay Garrulus glanbiomass of eaten carrion was determ ined under the assum ption that the bird ate it in the am ount of its daily dańus and Nutcracker Nucifraga caryocatactes), frogs Rana spp., and carrion of farm animals were considered prey food needs, that is, about 10% of its body mass (Fisher ests are dom inated by Scotch pine Pinns silvestns (80% of tree stands area) an d N orw ay spruce Picea abies (12%). Black alder Alnus glutinosa stands 3%, birch Betula ver rucosa — 3% and oak Quercus robur — 2%. Young for ests and forest plantations cover 26% of the area, whears old tree stands (> 80 yrs) — 22%.

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Diet of birds o f prey in W igry N ational Park

from open areas. Forest prey included Red Squirrel Sciurus vulgaris, Weasel Mustela nivalis, Hazel Grouse Bonasa bonasia, W oodcock Scolopax rusticola, thrushes Turdus spp., Hawfinch Coccothraustes coccothraustes and carrion of the Roe Deer Capreolus capreolus. The Musk Rat On datra zibethicus, W ater Vole Arvicola terrestris, waterfowl (Amtidae, Laridae), Coot Fulica atra and fish came from water habitats. The results of both methods were then compared.

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RESULTS Diet composition Black Kite. Twenty-three species of prey, belonging to six prey groups, were registered in the diet (Table 2). The m ost common prey were birds, prim arily water species: the gulls and ducks. The second im portant group of food was fish. Small m am m als and carrion of the larger m am m als supplem ented the diet.

Table 2. Diet composition of the Black Kite (data from pellets and prey remains). В — index of the food niche breadth, "+" — < 0.05%. Species

N

%N

4 1 1 1 7 14

3.7 1.0 1.0 1.0 6.5 13.2

3 3 3 1 5 4 1 1 1 2 2 1 3 1 10 41

2.8 2.8 2.8 1.0 4.8 3.8 1.0 1.0 1.0 1.9 1.9 1.0 2.9 1.0 9.6 39.3

2400 2100 3000 600 1375 1000 420 450 35 100 120 175 600 80 600 13055

10.9 9.5 13.5 2.7 6.2 4.5 1.9 2.0 0.2 0.5 0.6 0.8 2.7 0.4 2.7 59.1

2 2

1.9 1.9

30 30

0.2 0.2

Undetermined fish Total Fish

11 1 6 4 9 31

10.5 1.0 5.6 3.8 8.5 29.4

1350 100 1200 1600 2100 6350

6.2 0.5 5.4 7.2 9.5 28.8

Coleoptera Total Invertebrates

2 2

1.9 1.9

2 2

1 1 2 11 15

1.0 1.0 1.9 10.5 14.3

90 90 180 990 1350

105 3.6

100%

Talpa europaea Sciurus vulgaris Arvicola terrestris Rattus norvégiens

Undetermined small mammals Total M ammals Anas platyrhynchos Anas sp.

Domestic hen Fulica atra Larus ridibundus Lanis sp. Columba livia Columba sp. Alauda arvensis Turdus philomelos Turdus sp. Garrulus glandarius Pica pica Stumus vulgaris

Undetermined medium-sized birds Total Birds Rana sp. Total Am phibians Rutilus rutilus Scardinius erythrophthalmus Abramis brama Esox lucius

Felis catus Canis familiaris Sus domesticus

Carrion of mammals Total Carrion Total В

Biomass consumed (K) 320 300 80 250 350 1300

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221 kK 2.3

% biomass 1.4 1.4 0.4 1.1 1.6 5.9

+ + 0.4 0.4 0.8 4.4 6.0 100%

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Red Kite. Thirty-nine species, belonging to six prey groups, w ere found in the food (Table 3). Birds accounted for alm ost half of all prey. The share of m am m als w as also significant. Relatively high share

of carrion in the diet followed from eating dead ani m al bodies and from scavenging on throw n-aw ay rem ainders after the slaughter.

Table 3. Diet com position of the Red Kite (data from pellets and prey remains). В — index o f the food niche breadth, after Levins (1968), "+" — < 0.05%. Species

N 1

Talpa europaea Lepits sp. Lepus sp. juv. Sciurus vulgaris Ondatra zibethicus Arvicola terrestris Microtus sp. Rattus norvegicus M ustek nivalis

Undetermined small mammals Undetermined medium-sizedmammals Total M ammals Anas platyrhynchos Anas sp. Aythya sp. Perdix perdix

Domestic hen Fulica atra Vanellus vanellus Scolopax rusticola Larus ridibundus Larus sp. Columba livia Columba palumbus Columba sp. Turdus merula Turdus pilaris Turdus philomelos Turdus sp. Garrulus glandarius Pica pica Nucifraga caryocatactes Corvus monedula Corvus frugilegus Corvus corax Coccothraustes coccothraustes Emberiza citńnella

Undetermined medium-sized-birds Total Birds Rana sp. Total Am phibians Rutilus rutilus Abramis brama Esox lucius

Cyprynidae Undetermined fish Total Fish

%N

Biomass consumed W 4

% biomass

2 5 10 1 5 11 10 10 17 1 78

3 0.9 1.9 0.2 0.9 2.1 1.9 1.9 3.2 0.2 14.6

400 10000 200 1500 7700 800 320 4250 85 3900

5 0.4 9.0 0.2 1.3 6.9 0.7 0.3 3.8 0.1 3.5

2 150

0.4 28.2

400 29555

0.4 26.6

7 7 1 3 20 8 4 1 9 9 4 2 10 6 3 1 18 17 1 1 8 18 1 4 1 91 255

1.3 1.3 0.2 0.6 5.6 1.5 0.8 0.2 1.7 1.7 0.8 0.4 1.9 1.1 0.6 0.2 3.3 3.2 0.2 0.2 1.5 3.3 0.2 0.8 0.2 17.1 48.0

5600 4900 600 1200 15000 4800 600 300 2475 2250 1680 950 4500 420 210 50 1080 2975 200 200 1600 8100 1100 220 30 5460 66500

5.0 4.4 0.5 1.1 13.5 4.3 0.5 0.3 2.2 2.0 1.6 0.8 4.1 0.4 0.2 + 1.0 2.7 0.2 0.2 1.5 7.3 1.0 0.2 + 4.9 59.9

9 9

1.7 1.7

135 135

0.1 0.1

4 1 3 2 9 19

0.7 0.2 0.6 0.4 1.7 3.6

800 500 1000 700 2700 5700

0.7 05 0.9 0.6 2.4 5.1

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Diet o f birds o f prey in W igry N ational Park

1 Melolontha sp.

Coleoptera Total Invertebrates Canis familiaris Felis całus Ovisaries Sus domesticus Capreolus capreolus

Refuse from slaughter-house Carrion of domestic animals Carrion of undetermined mammals Domestic hen Total Carrion Total В

2

69

4 2 6

3 0.8 0.4 1.2

4 4 2 6

2 1 4 3 1 6 7 58 10 92

0.4 0.2 0.8 0.6 0.2 1.1 1.3 10.9 1.9 17.3

200 100 400 300 100 600 700 5800 1000 9200

531 2.8

100%

White-tailed Eagle. There w ere 24 species of prey, am ong which the m ost num erous group were birds and the next — fish. They accounted together for over 95% of prey in term s of both the num ber of items and their biomass. The share of m am m als and carrion was insignificant (Table 4). Lesser Spotted Eagle. In the diet 18 species of ani mals were found (Table 5). M am m als accounted for more than half of all prey. The share of birds was rela tively high. The Lesser Spotted Eagle caught num erous frogs and insects b u t they had small share in the bio mass of the food. Fish and carrion were not found in its diet. Size of prey Am ong the studied birds of prey, the White-tailed Eagle caught the largest prey while the Lesser Spotted Eagle — the smallest. Preys of both Kite species were characterized by interm ediate biomass (Table 6). The m ost pronounced difference between the body mass of prey from various system atic groups was found in the case of the Black Kite. Differences between the mass of mammals, birds, and fish caught by the White-tailed Eagle and the Red Kite were small (Table 6). In the diet of the Black Kite, prey items with mass 101-500 g were the m ost num erous. The Red Kite caught the most often prey w ith m ass 1-100 g and 101-500 g. The body m ass of the Lesser Spotted Eagle's prey in m ost cases did not exceed 100 g. Vertebrates with mass over 500 g dom inated in the diet of the W hite-tailed Eagle (Fig. 1). Frequency distributions of prey grouped in classes of body m ass differed statistically betw een all the raptor species studied (from 21.8 to 235.7, df = 2,

111.1 kg 2.2

5 + +

0.2 0.1 0.3 0.3 0.1 0.5 0.6 5.2 1.0 8.3 100%

p < 0.001 in pairwise comparisons, G-test for homogenity of percentages). Foraging habitats The Black Kite got m ost of its food in w ater habitats (Table 7). It preyed on the forest edge, on the lakes or on farmlands. M any observations referred to the birds in an open habitat w here the Kite was seen patroling a busy road segm ent or picking u p carrion of animals run over by vehicles. During the breeding period Black Kites were seen u p to 4 km aw ay from the nest. The Red Kite got the food prim arily in open areas. Over half of prey in term s of both the num ber of items and the biomass comes from this habitat. The Red Kite was the raptor the m ost strongly connected with an thropogenic habitat. Dum ping grounds located near hum an settlements were an essential source of its food. Lakes w ere another im portant feeding area for this raptor. More than one-fourth of all prey came from there (Table 7). Preying Red Kites were observed in all types of W N P's habitats. They were seen generally in a patrol flight over open areas near forest edge and over the lakes (Table 7). Red Kites were also observed flying low over areas of slaughter-houses and picking up the food from an urban dum ping ground about 10 km away from the nest. During preying on the rodents the Red Kite often w as on the watch on single trees in farmlands. The W hite-tailed Eagle w as a raptor very strongly connected w ith the lakes. It got the food alm ost ex clusively in w ater habitat (Table 7). Alm ost all obser vations of W hite-tailed Eagles referred to birds prey ing on the lakes, a river or sitting on trees growing

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Table 4. Diet com position of the W hite-tailed Eagle (data from pellets and prey remains). В — index of the food niche breadth, "+" — < 0.05%. Species

N

%N

Erinaceus concolor

1 3 1 1 2 8

0.3 1.0 0.3 0.3 0.8 2.7

200 3000 300 30 1000 4530

0.1 1.7 0.2 + 0.6 2.6

2 1 2 9 27 5 3 1 2 1 132 1 3 1 1 6 197

0.8 0.3 0.8 3.0 9.0 1.6 1.0 0.3 0.8 0.3 44.1 0.3 1.0 0.3 0.3 2.0 65.9

1400 200 1000 7200 18900 3500 2100 1000 840 1000 79200 475 180 175 200 3000 120370

0.8 0.1 0.6 4.2 11.0 2.1 1.2 0.6 0.5 0.6 46.0 0.3 0.1 0.1 0.1 1.7 70.0

4 1 33 8 10 8 3 21 2 90

1.3 0.3 11.0 2.6 3.3 2.6 1.0 7.0 0.8 30.1

600 150 17900 4800 4500 5200 600 10500 2000 46250

0.3 0.1 10.4 2.8 2.6 3.0 0.3 6.1 1.2 26.8

Odonate Total Invertebrates

1 1

0.3 0.3

1 1

+ +

Egg of ducks Total Eggs

1 1

0.3 0.3

40 40

+ +

Canis familiaris

1 1 2

0.3 0.3 0.8

500 500 1000

Lepus europaeus Sciurus vulgaris Microtus sp.

Undetermined mammals Total M ammals Podiceps cristatus Podiceps cristatus pull. Cygnus ob r pull. Anas platyrhynchos Anas sp. Aythya fuligula Aythya sp. Buteo buteo Bonasa bonasia

Domestic hen Fulica atra Columba palumbus Turdus sp. Garrulus glandańus

Undetermined medium-sized-birds Undetermined big birds Total Birds Rutilus rutilus Scardinius erythrophthalmus Abramis brama Anąuilla anquilla Perea fluviatilis Esox lucius

Undetermined small fish Undetremined medium-sized-fish Undetermined big fish Total Fish

Capreolus capreolus

Total Carrion Total В

299 1.9

near the banks of w ater bodies. The W hite-tailed Ea gle preyed u p to 15 km aw ay from the nest b u t the m ost often w ithin a radius of about 5 km. It w as the only species that such com m on preying of a pair was observed.

100%

Biomass consumed

1722 kR 1.8

% biomass

0.3 0.3 0.6 100%

The Lesser Spotted Eagle preyed in open areas and in forest. Prey caught on the fields or m eadow s dom i nated in its food (Table 7). The Lesser Spotted Eagle was observed prim arily in open areas. While preying, the bird circled over a field or a m eadow , sat on a

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D iet o f birds o f prey in W igry N ational Park

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Table 5. Diet composition of the Lesser Spotted Eagle (data from pellets and prey remains). В — index of the food niche breadth. Species

N

%N

14 1 1 1 3 3 8 18 1 1 1 94 3

4.8 0.3 0.3 0.3 1.0 1.0 2.8 6.2 0.3 0.3 0.3 2.1 1.0

1 150

0.3 51.2

200 5922

2.0 59.2

Undetermined small birds Undetermined medium-sized birds Total Birds

1 1 1 1 1 2 2 1 35 6 51

0.3 0.3 0.3 0.3 0.3 0.7 0.7 0.3 11.9 2.1 17.4

400 500 475 70 35 100 350 500 700 360 3490

4.0 5.0 4.7 0.7 0.3 1.0 3.5 5.0 7.0 3.6 34.8

Rana sp. Total Am phibians

36 36

12.3 12.3

540 540

5.4 5.4

Coleoptera Total Invertebrates

56 56

19.1 19.1

56 56

0.6 0.6

293 2.9

100%

100 kg 2.1

Talpa europaea Lepus europaeus juv. Clethrionomys glareolus Ondatra zibethicus Arvicola terrestris Microtus oeconomus Microtus arvalis Microtus sp. Apodemus flavicollis Apodemus sp.

Muridae Undetermined small rodents Undetermined small mammals Undetermined medium-sizedmammals Total M ammals Perdix perdix

Domestic hen juv. Columba palumbus Detidrocopos major Alauda arvensis Turdus philomelos Garrulus xlandarius Coruus corax pull.

Total В

branch of a tree grow ing on forest edge or walked on the ground, collecting insects and frogs. Preying Lesser Spotted Eagle w ere m et up to 4 km aw ay from the nest. However, m ore than 50% of the observations comes from the distance not more than 1 km. Food niche overlaps The food niches of studied species overlapped to various degrees, b u t all the raptors fed at least in half on the same kind of food. The food niches of the Black Kite and W hite-tailed Eagle overlapped the m ost (Table 8). W ater birds and fish prevailed in the diet of both species b u t in the case of the White-tailed Eagle the dom ination of these food groups was much

Biomass consumed (K) 1120 200 20 700 240 126 160 576 30 25 25 2350 150

% biomass 11.1 2.0 0.2 7.0 2.4 1.3 1.6 5.8 0.3 0.3 0.3 23.4 1.5

100%

stronger. The niches of both Kites and of the Red Kite and W hite-tailed Eagle and also of the Red Kite and Lesser Spotted Eagle also overlapped to a large degree. The food niches of both Eagles and those of the Black Kite and Lesser Spotted Eagle were the most separated (Table 8).

DISCUSSION The diet of the all studied birds of prey is charac terized by relatively large variability dependent on the habitat conditions. Both Kites feed on mam m als, birds, fish, and carrion. Locally they supplem ent the

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72

Spain, a high share of carrion (30-55%) w as found in the w inter food of the Red Kite (Garcia et al. 1998). W ater birds and fish dom inate in the W hite-tailed Eagle's diet. The share of both groups is variable and ranges from several to 90%. In some areas, Table 6. A verage body m ass (g) of preys (carrion excluded), taken by four carrion is also an essential com ponent of the raptor species studied. food (Cram p «Sc Simmons 1980, Fischer 1984, Gensbol & Thiede 1986, Wacławek et al. Total prey Bird Fish Mammal Raptor species 230 94 318 205 Milvus migrans 1998, Mizera 1999). In Pisz Forest, fish ac 232 197 261 300 Mikrus mikrus counted for 74%, and birds for 22% of the 514 578 611 566 Haliaeełus albicilla White-tailed Eagle's prey (Wacławek et al. 34 39 68 Aquila pomańna 1998). In WNP, the White-tailed Eagle caught birds much more often than fish. The Lesser Spotted Eagle feeds on small S Black Kite rodents, birds, reptiles, am phibians, and □ Red Kite 100 т □ W hite-tailed Eagle insects (Palasthy & M eyburg 1973, C ram p ? Ф 80 4Ш Lesser Spotted Eagle E & Sim m ons 1980, Gensbol & Thiede 1986). о 60 f Shares of particular food groups vary. In ato > 40 i Białowieża Prim eval Forest, small m am 0) a m als accounted for 27-35% of the food о а® biom ass, birds — 30%, reptiles — 5%, frogs H I 0 —J — 3-5% (Jędrzejewska & Jędrzejewski 101-500 >500 1-100 1998). In Pisz Forest, m am m als accounted prey body mass (g) for 62% (including voles — 20% and mole Fig. 1. Percentage frequencies of prey specimens, captured by four raptor species in — 11%), birds — 34%, reptiles — 3% of the Wigry National Park, in 3 classes of body mass. biom ass of the Lesser Spotted Eagle's food (I. M irowski, unpubl. data). Sim ilar proportions of the Thiede 1986, Ortlieb 1989, Veiga & H iraldo 1990, m ain food groups w ere found in region of M azowsze, Blanco & H iraldo 1992, Jędrzejew ska & Jędrzejewski C entral Poland (I. M irowski, unpubl. data). 1998). In south-w estern Spain and in Białowieża Pri All studied species use diversified ways of preying m eval Forest, sim ilarly as in this paper, the share of and getting the food, observed also in WNP: patrol w ater species in the diet of the Black Kite w as found flight, sit-and-w ait tactic, and walking on the ground in higher than in the diet of the Red Kite (Veiga & a search for less timid prey (Gensbol & Thiede 1986, H iraldo 1990, Jędrzejew ska & Jędrzejewski 1998). In Mebs 1998). N um erous researchers published infor the food of the Black Kite an d Red Kite in Białowieża m ation about preying of W hite-tailed Eagles in pairs Prim eval Forest carrion did not appear at all (Jędrze (Fischer 1984, Giergielewicz 1985, Gensbol & Thiede jewska & Jędrzejew ski 1998), w hile it w as an essential 1986, M izera 1999). The Red Kite, Black Kite and com ponent of the food of both species in WNP. In

diet w ith am phibians, reptiles, and invertebrates. Data from literature show s that proportions of p ar ticular food groups in various areas vary (Cram p & Sim m ons 1980, Delibes & Garcia 1984, Gensbol &

ф

20i

Table 7. Percentage of prey in diets (% PD) of four raptors from three habitats compared with the percentages of observations of birds (% Ob) hunting in those habitats. NP — number of prey specim ens found in pellets and prey remains; NO b — number of observations; D:Ob — mean difference betw een analysis of diet com position and visual observations. Raptor species M ilvus migrans M ilvus milvus Haliaeetus albicilla Aquila pomańna

D:Ob (SD)

NP 86 289 295 78

NOb 35 103 27 42

Open areas % PD (% Ob) 27 (55) 52 (77) 2 (5) 84 (93) +16(12)

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Lake % PD (% Ob) 66 (36) (15) 28 94 (95) 4 (0) -12 (13)

% PD 7 20 4 12

Forest (% Ob) (9) (8) (0) (7) -6 (4 )


White-tailed Eagle sometimes use kleptoparasitism (Cramp & Simmons 1980, Fischer 1984, Ortlieb 1989). Taking the food from other birds species was not seen in Wigry National Park. Table 8. Food niche overlaps of the four raptor species studied. Pair of species

M . milvus

И . albicilla

A. pomarina

Milvus migrans M ilvus milvus

0.880 X

0.991 0.878 X

0.528 0.816 0.502

Haliaeetus albicilla

The Black Kite preys predom inatingly in open areas or over w ater (Gensbol & Thiede 1986, Mebs 1998). The Red Kite preys in open areas, readily uses places of throwing out food waste and dum ping grounds. It eats animals killed by cars and farm ing machines. It gets its food up to 10-15 km aw ay from the nest (Ortlieb 1998). The W hite-tailed Eagle preys almost exclusively on w ater bodies. It can search for food up to 20 km away from the nest (Mebs 1998, M izera 1999). However, it w as found in Germ any that the maximal distance be tween the nest and the m ain feeding ground was 3 km, even if W hite-tailed Eagles preyed also 6-11 km away from the breeding place (Gensbol & Thiede 1986). The Lesser Spotted Eagle searches for the food in open wetlands or in the fields (Pugacewicz 1996,1. Mi rowski unpubl. data). In Białowieża Primeval Forest, the Lesser Spotted Eagle preyed generally in wet meadows, river valleys and on forest edges. The birds preyed within a radius of 3 km from the nest. However, single observations referred to birds bringing the food from the distance of over 6 km (Pugacewicz 1996). In region of Mazowsze, Lesser Spotted Eagels preyed not more than 3 km away from the nest (I. Mirowski unpubl. data). Application in this study of two assessment methods of using the habitats by raptors (Table 7) allowed de termining the real habitat selectivity. The results of both assessment m ethods were consistent only for the White tailed Eagle. For the Kites and Lesser Spotted Eagle ob servations performed in open areas overestimated the degree of usage of this habitat due to better visibility of preying birds and more often penetration of this habitat by an observer. Observations of preying birds on the lakes and in forest led to underestimate the share of food from these habitats in the diet (Table 7). Is was the result of strong restrictions on the field of vision in the forest and the possibility of performing observations only from

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the bank of a lake. The way of using the habitat of birds of prey in WNP is similar to the results of observations published by another researchers. Among the raptors studied in Wigry National Park, the White-tailed Eagle was the most specialised species. This bird used for preying only one habitat and had the narrowest food niche. Maybe the food niche breadth of the White-tailed Eagle was slightly underestimated due to classifying by the author food eaten as carrion as preyed birds or fish. According to numerous researchers, the White-tailed Eagle generally eats carrion in winter, but it can also feed on carrion during the breeding period (Cramp & Simmons 1980, Fischer 1984, Mizera 1999). The Black Kite, Red Kite and Lesser Spotted Eagle were opportunists w ith respect to their feeding habits. Their food niche breadth in term s of the num ber of prey items was in W NP m uch higher than in the case of the W hite-tailed Eagle. The differences in the niche breadth in term s of the food biomass between the White-tailed Eagle and the other raptors were not very high. In WNP, the food niches of both Kite species and the W hite-tailed Eagle overlapped considerably. The food niche of the Lesser Spotted Eagle was more sepa rated. Its prey items w ere m uch smaller and less timid than in the case of the other raptors. Contrary to the Kites and White-tailed Eagle, the Lesser Spotted Eagle did not prey on the lakes. According to Jędrzejewska & Jędrzejewski (1998) in Białowieża Primeval Forest (where the Kites and Lesser Spotted Eagles nested) the niches of the Red Kite and Lesser Spotted Eagle coin cided the most, next the niches of the Red and Black Kites. The niches of the Black Kite and Lesser Spotted Eagle overlapped the least. The raptors in W NP compensated for the strong co incidence of their food niches by space separation of the feeding grounds. They preferred catching of prey with different body size, proficiency of moving, and timidity. The birds used various strategies to get the food. Translated by Dr A rtur Mikitiuk

ACKNOWLEDGEMENTS I sincerely thank Prof. Dr hab. Jacek Goszczyński for his help in methodological m atters and critical comments on the earlier version. I am most grateful to

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D. Zaw adzka

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my husband, Jerzy, w ho provided invaluable help during the field w ork and support at all stages of this paper preparations. I thank Dr hab. Bogumiła Jędrze jewska for her help in the data analysis, Jarosław Bore jszo and Jacek Łoziński for their assistance in the field work, and M ałgorzata Rabczuk for draw ing the figure.

Veiga J. P., Hiraldo F. 1990. Food habits and tht survival and growth of nestlings in two sympatric kites (M ilvis milvus and M ilvus migrans). Holarctic Ecology 13:62-71. Wacławek K., Zub K., Trznadel-Wacławek M, Terlecki J. 1998. [White-tailed Eagle's diet in breeding season in Pisz Forest (NE Poland) in 1994-96]. Pol. Tow. Ekol. Biul. 5:48-49.

STRESZCZENIE REFERENCES Blanco J. C ., Hiraldo F. 1992. On the influence of the red kite Milvus milvus L. on the small game in a Mediterranean area of southern Spain. In: Bobek В., Perzanowski K., Regelin W. (eds.). Świat Press. Kraków, pp.: 577-581. Busse P. (ed.). 1990. Mały słownik zoologiczny. Vol. 1-2. Wiedza Powszechna. Warszawa. Cramp S., Simmons K. 1980. The Birds of the Western Palearctic Vol. II. Oxford. Delibes M., Garcia L. 1984. [Food habits of the Red Kite in Donana during the breeding period]. Ardeola 31:115-121. Fischer W. 1984. Die Seeadler. Ziemsen Verlag. Wittemberg. Garcia J. T., Vinuela J., Sunyer C. 1998. Geographic variation of the winter diet of the RedKite Milvus milvus in the Iberian Peninsula. Ibis 140:302-309. Gensbol B., Thiede W. 1986. Greifvoegel. BLV Verlagsgesellachaft Muenchen-Wien-Zurich. Giergielewicz J. 1985. [Observations on the methods of hunting on waterfowl by White-tailed Eagle at "Lake Świdwie" Nature Reserve). Not. om. 26:169-176. Goszczyński J. 1974. Studies on the food of foxes. Acta theriol. 21: 527-534. Jędrzejewska В., Jędrzejewski W. 1998. Predation in vertebrate communities.The Białowieża Primeval Forest as a case study. Springer Verlag. Berlin. Komitet Ochrony Orłów 1995. Biuletyn 7. Levins R. 1968. Evolution in changing environments. Princeton University Press. Princeton. Mebs T. 1998. Ptaki drapieżne Europy. Multico. Warszawa. Mizera T. 1999. Bielik. Lubuski Klub Przyrodników. Świebodzin. Mrugasiewicz A. 1984. [White-tailed Eagle Haliaeetus albicilla in Barycz valley]. Dolina Baryczy 3:19-23. Ortlieb R. 1989. Die Rotmilan. Ziemsen Verlag. Wittemberg. Palasthy ]., M eybuig B. 1973. Zur Emeahrung des Schreiadlers (Acjuila pormrim) in der Ostslovakei unter atypischen klimatischen bedingungen. Om. Mitteil. 4:63-71. Pianka E. R. 1973. The structure of lizard communities. Annu. Rev. Ecol. Syst. 4,53:74. Pielowski Z. 19%. Ptaki drapieżne. Wyd. Świat. Warszawa. Pugacewicz E. 19%. [Birds of prey breeding in the Polish part of the Białowieża Primeval Forest]. Not. om. 37:173-224. Sokal R. R., Rohlf F. J. 1981. Biometry. W. H. Freeman and Company. N ew York.

[Zwyczaje żerow iskow e kani czarnej, kani rudej, b ielika i orlika krzykliw ego w W igierskim Parku Narodowym] Badania prow adzono w okresie 2-7 lat w sezonie lęgowym (tab. 1). Szukano zajętych gniazd ptaków drapieżnych i kontrolowano je. Analizowano resztki pokarm u i wypluw ki znalezione w gniazdach i na ziemi. Skład pokarm u oznaczano ilościowo, identyfiku jąc spożyte ofiary na podstaw ie znalezionych resztek (piór, sierści, szkieletów, łusek). Przy oznaczaniu bio m asy zjedzonej padliny założono, że ptak zjadał ją w ilości równej dobow em u zapotrzebowaniu pokar mu, czyli ok. 10% masy ciała (Fisher 1984, Busse 1990, Pielowski 1996). Przyjęto, że jednorazowa konsumpcja padliny dużych kręgowców wynosiła 90 g dla kani czarnej, 100 g dla kani rudej oraz 500 g dla bielika. Obliczono szerokość nisz pokarmowych badanych gatunków ptaków drapieżnych oraz oceniono stopień ich nakładania się. W skaźnik szerokości niszy pokar mowej (B) obliczano w g Levinsa (1968): В = 1 /Ip ,2, gdzie p. jest udziałem każdej z 6 wyróżnionych grup pokarmu (ssaków, ptaków, ryb, padliny, płazów i owa dów) w łącznej liczbie ofiar oraz w całkowitej biomasie konsum owanego pokarm u. Dla wyróżnionych 6 grup wskaźnik В może przyjmować wartości od 1 (najwęższa nisza) do 6 (najszersza możliwa nisza). Wskaźnik nakładania się nisz pokarmowych dw óch gatunków był obliczany wg. Pianki (1973): ol = I (ри x Pp x [(Lpu2) x (Lp *) V n, gdzie cl jest wskaźnikiem na kładania się nisz pom iędzy gatunkiem i oraz gatun kiem j, p.a jest udziałem я-tej grupy ofiar w łącznej bio masie pokarm u i-tego gatunku gatunku drapieżnika, p^ jest udziałem д-tej grupy ofiar w łącznej biomasie po karm u j-tego gatunku drapieżnika. Wskaźnik a przyj muje wartości od 0 (nisze pokarm ow e odrębne) do 1 (nisze pokarm owe identyczne). W trakcie badań obserw ow ano żerujące ptaki, określano sposób i miejsce polow ania oraz oddalenie

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żerow iska od gniazda. Przeprow adzono ocenę w y biórczości środow iskow ej opartą na udziale w po karm ie ofiar, chw ytanych w środow isku polnym , leśnym i w odnym . W pokarm ie kani czarnej stwierdzono 23 gatunki ofiar. Najczęstszą zdobyczą były ptaki, następnie ryby (tab. 2). W pożyw ieniu kani rudej wystąpiło 39 gatun ków ofiar. Blisko połowę wszystkich zdobyczy sta nowiły ptaki. Istotny był udział w diecie ssaków oraz padliny (tab. 3). Bielik polował na 24 gatunki ofiar, wśród których najliczniejszą zdobyczą były ptaki, na stępnie ryby (tab. 4). W pokarm ie orlika krzykliwego stw ierdzono 18 gatunków zwierząt. Ponad połowę wszystkich ofiar stanowiły ssaki (tab. 5). Największe ofiary chwytał bielik, najmniejsze orlik krzykliwy. Pośrednią wielkość miały zdobycze kani rudej i czarnej (tab. 6). Najliczniejsze ofiary kani czarnej miały m asę 101-500 g, kani rudej: 1-100 g, następnie 101-500 g. Masa zdobyczy bielika najczęściej przekra czała 500 g, a orlika krzykliwego — wynosiła mniej niż lOOgOryc. 1). Kania czarna największą część pokarm u zdobywała nad w odą (tab. 7). Żerowała w odległości do 4 km od gniazda. Kania ruda żerowała przede wszystkim na terenach otwartych (tab. 7). Chętnie wykorzystywała w ysypiska śmieci i odpadków . Zdobyw ała pokarm w odległości do 10 km od gniazda. Bielik polował wy

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łącznie nad jeziorami lub rzeką (tab. 7). Obserwowano w spólne polow anie pary ptaków . Bieliki żerowały w odległości do 15 km od gniazda. Orlik krzykliwy zdobyw ał pokarm na terenach otwartych oraz w lesie (tab. 7). Żerował w odległości do 4 km od gniazda, jednak najczęściej nie dalej niż 1 km. Najmniejszą szerokość niszy pokarmowej stwier dzono u bielika. Szerokości nisz pokarmowych pozo stałych ptaków drapieżnych były zbliżone. Nisze pokarm ow e badanych ptaków drapieżnych, oceniane pod względem biom asy głównych ofiar, na kładały się co najmniej w połowie (tab. 8). Najsilniejsze pokrywanie się nisz stw ierdzono u kani czarnej i bieli ka. W dużym stopniu pokryw ały się także nisze oby dw u kań oraz kani rudej i bielika. Najbardziej rozdzie lone były nisze pokarm ow e bielika i orlika oraz kani czarnej i orlika (tab. 8). Najsilniej wyspecjalizowanym gatunkiem był bielik. Kania ruda i czarna oraz orlik krzykliwy były gatunkam i oportunistycznym i pod względem sposobu odżywiania. Silne pokrywanie się nisz pokarmowych ptaki drapieżne w W PN kom pensowały rozdzieleniem przestrzennym żerowisk. Preferowały chwytanie ofiar różniących się rozm iaram i ciała oraz sprawnością po ruszania się i płochliwością. W ykorzystywały różno rodne strategie zdobyw ania pokarmu.

fyh'SZ Rys. A. Dmoch

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