Buteo Lagopus Research Articles

The Avifauna of the Lake Yeongam region and the Surrounding Reclaimed Arable Land

This study was conducted seasonally between May and December of 2009 on the avifauna of the Lake Yeongnam (Yeongamho), Jeollanam-do region and the surrounding reclaimed arable land area. The study observed a total of 167,675 birds of 98 species, 29 families and 13 orders. The most dominant species was the baikal teal (Anas Formosa) at 150,000 counts (89.46%), followed by, in decreasing order, the bean goose (Anser fabalis) at 3,175 counts (1.89%) and the mallard (Anas platyrhynchos) at 1,869 counts (1.11%). In terms of the individual seasons, winter showed the highest species and individual bird counts among all four seasons at 104,710 birds of 59 species. A total of 14 government protected bird species, including the Chinese egret, bean goose, baikal teal, cinereous vulture, hen harrier, sparrow hawk, northern goshawk, common buzzard, rough-legged buzzard, imperial eagle, peregrine falcon, common kestrel, merlin and the long-billed ring plover, were observed during the study.

Association of wintering raptors with Conservation Reserve Enhancement Program grasslands in Pennsylvania

Conservation grasslands can provide valuable habitat resource for breeding songbirds, but their value for wintering raptors has received little attention. We hypothesized that increased availability of grassland habitat through the Conservation Reserve Enhancement Program (CREP) has resulted in an increase or redistribution in numbers of four species of raptors in Pennsylvania since 2001. We tested this by analyzing winter raptor counts from volunteer surveys, conducted from 2001 to 2008, for Red-tailed Hawks (Buteo jamaicensis), Rough-legged Hawks (Buteo lagopus), Northern Harriers (Circus cyaneus), and American Kestrels (Falco sparverius). During that period, numbers of wintering Northern Harriers increased by more than 20% per year. Log-linear Poisson regression models show that all four species increased in the region of Pennsylvania that had the most and longest-established conservation grasslands. At the county scale (N = 67), Bayesian spatial models showed that spatial and temporal population trends of all four species were positively correlated with the amount of conservation grassland. This relationship was particularly strong for Northern Harriers, with numbers predicted to increase by 35.7% per year for each additional 1% of farmland enrolled in CREP. Our results suggest that conservation grasslands are likely the primary cause of the increase in numbers of wintering Northern Harriers in Pennsylvania since 2001.

Serological and Parasitological Prevalence of Toxoplasma gondii in Wild Birds From Colorado

Ground-feeding birds are considered important in the epidemiology of Toxoplasma gondii because they serve as indicators of soil contamination by oocysts, and birds of prey are indicators of T. gondii prevalence in rodents and other small mammals. Cats excrete environmentally resistant oocysts after consuming tissues of T. gondii -infected birds. In the present study, sera and tissues from 382 wild birds from Colorado were tested for T. gondii infection. Antibodies to T. gondii were found in 38 birds with the use of the modified agglutination test (MAT, 1∶25 titer). Tissues (brains, hearts) of 84 birds were bioassayed in mice. Viable T. gondii was isolated from 1 of 1 barn owl (Tyto alba), 1 of 5 American kestrels (Falco sparverius), 1 of 7 ferruginous hawks (Buteo regalis), 1 of 4 rough-legged hawks (Buteo lagopus), 2 of 13 Swainson's hawks (Buteo swainsoni), and 1 of 25 red-tailed hawks (Buteo jamaicensis). This is the first time T. gondii has been isolated from the barn owl, ferruginous hawk, rough-legged hawk, and Swainson's hawk.

Effectiveness of Raptor Perch Deterrents on an Electrical Transmission Line in Southwestern Wyoming

ABSTRACT In sagebrush—steppe and other open habitats, power lines can provide perches for raptors and other birds in areas where few natural perches previously existed, with potential negative impacts for nearby prey species, such as greater sage‐grouse (Centrocercus urophasianus). Between September 2006 and August 2007, we used driving surveys, behavioral‐observation surveys, and prey‐remains surveys to assess the ability of perch‐deterrent devices to minimize raptor and common raven (Corvus corax) activity on a recently constructed transmission line in southwestern Wyoming. All survey methods demonstrated that activity was significantly lower on the deterrent line compared with a nearby control line; however, deterrent devices did not entirely prevent perching. Considering use of cross‐arms or pole‐tops alone, we sighted 42 raptors and ravens on the deterrent line and 551 on the control line during 192 driving surveys of each line. Golden eagles (Aquila chrysaetos) and ravens were the species most commonly observed successfully overcoming deterrent devices. Smaller rough‐legged hawks (Buteo lagopus) regularly avoided deterrents by perching on conductors (i.e., wires). We documented much off‐line activity near both survey lines and suggest that fewer birds near the deterrent line likely reflected reduced availability of nearby alternate perches. There was a pronounced winter peak in on‐line perch use, with the effect more evident on the control line. Behavior surveys corroborated our driving‐survey results but were otherwise unproductive. During 549 prey‐remains surveys of each line, we found 9 single and 60 grouped prey items near deterrent‐line poles, compared with 277 single and 467 grouped items near control‐line poles. We observed few sage‐grouse in the study area but did witness a likely power line—related, raptor‐caused sage‐grouse mortality. Overall, our results suggest that perch‐deterrent devices can reduce raptor and raven activity on power‐line structures, but to determine their utility on entire power‐line segments, we suggest managers consider 1) what level of reduction in perch activity is worth the cost, and 2) the availability of alternate perches in the surrounding landscape.

Seasonal Differences in Migration Counts of Raptors: Utility of Spring Counts for Population Monitoring

Long-term monitoring is important for ensuring effective conservation of raptor populations. Raptors also can serve as indicators of biodiversity and ecosystem condition. Therefore, effective monitoring of raptor populations yields the added benefit of helping to evaluate the status of ecosystems. Spring counts of migrating raptors at concentration points may contribute to these goals, particularly by providing insight into the vital demographic rates underlying population trends. Although much is known about the monitoring value of autumn migration counts in North America, little research has addressed the value of spring counts. We compared counts at seven spring watchsites to those at seven autumn watchsites matched by region (Southwest, Great Lakes, and Northeast) to assess the value of spring counts for population monitoring. Our analyses suggested that population indexes derived from spring migration counts provided estimates of population change that differed overall from autumn migration counts in the same region. The concordance of spring and autumn trends was higher in the Southwest and Northeast than in the Great Lakes region, suggesting greater variation in the seasonal representation of populations in the latter region. The average precision of spring trend estimates was better than for autumn estimates in the same region in two of three regions, and the estimated rates of change often were lower in spring. Spring counts enhanced the ability to estimate population trends for species that are less common in autumn counts, including the Rough-legged Hawk (Buteo lagopus) and Red-shouldered Hawk (B. lineatus). To realize fully the value of spring counts, we recommend the establishment of additional spring watchsites in areas that concentrate migrants in autumn, but do so to a lesser extent in spring, as well as additional research to define the populations sampled by autumn and spring counts.

Detection Probability of Cliff-Nesting Raptors During Helicopter and Fixed-Wing Aircraft Surveys in Western Alaska

Abstract We conducted repeated aerial surveys for breeding cliff-nesting raptors on the Yukon Delta National Wildlife Refuge (YDNWR) in western Alaska to estimate detection probabilities of Gyrfalcons (Falco rusticolus), Golden Eagles (Aquila chrysaetos), Rough-legged Hawks (Buteo lagopus), and also Common Ravens (Corvus corax). Using the program PRESENCE, we modeled detection histories of each species based on single species occupancy modeling. We used different observers during four helicopter replicate surveys in the Kilbuck Mountains and five fixed-wing replicate surveys in the Ingakslugwat Hills near Bethel, AK. During helicopter surveys, Gyrfalcons had the highest detection probability estimate (; = 0.79; SE 0.05), followed by Golden Eagles ( = 0.68; SE 0.05), Common Ravens ( = 0.45; SE 0.17), and Rough-legged Hawks ( = 0.10; SE 0.11). Detection probabilities from fixed-wing aircraft in the Ingakslugwat Hills were similar to those from the helicopter in the Kilbuck Mountains for Gyrfalcons a...

White-fronted and bean geese breeding near snowy owls, peregrine falcons, and rough-legged buzzards at the Taimyr Peninsula

Studies were carried out in 2000-2007 near Medusa Bay (73.21' N, 80.32' E) and along the Agapa River (from 70 degrees 11', 86 degrees 15' E. down to the mouth 71 degrees 26' N, 89 degrees 13' E), in the northwestern and central parts of the Taimyr Peninsula. White-fronted goose nests are usually spread in the tundra or placed in 1-3 nest colonies near nests or staging points of snowy owls, peregrine falcons, or rough-legged buzzards. The intent of white-fronted geese to breed near birds of prey or owls increases sharply when arctic fox numbers are high. In the area near Medusa Bay, white-fronted geese nest much closer to peregrine falcon nests than in the area along the Agapa River. At the latter location, white-fronted geese lose the competition to red-breasted geese, which are more numerous here. Bean geese, in spite of their greater size and ability to protect their nests against arctic foxes, really tend to breed near peregrine falcons or buzzards, where they manage to compete with red-breasted geese.

Red-breasted goose colonies on the Taimyr Peninsula: Factors responsible for the proximity of goose nests to nests of peregrine falcons, rough-legged buzzards, and snowy owls

Red-breasted goose colonies have been studied near Medusa Bay (73 degrees 21' N, 80 degrees 32' E), on the northwestern Taimyr Peninsula, and along the Agapa River (70 degrees 11' N, 86 degrees 15' E) down to its mouth (70 degrees 26' N, 89 degrees 13' E), in the central Taimyr Peninsula. Red-breasted geese nesting near peregrine falcons are protected by the falcons from arctic foxes; however, they are sometimes attacked by the falcons themselves. In the colonies near peregrine falcon nests, the vast majority of goose nests were situated no farther than 100 m from the falcon nest. When food is abundant, falcons protect a larger area around their nest. The distance between the falcon nest and the surrounding goose nests is inversely related to the falcon's activity. In years of higher falcon activity, falcons prevent red-breasted geese from nesting as close to their nest as in years of lower falcon activity. Additional stimuli are required for red-breasted geese to form colonies near rough-legged buzzard nests. The distance between snowy owl nests and red-breasted goose nests was smaller when arctic foxes were abundant than when they were scarce.

Selected radionuclides and heavy metals in skeletons of birds of prey from eastern Poland

Results of determination of 137Cs, 90Sr, 40K, 239+240Pu, and heavy metals: Mn, Zn, Pb, Cd, Ni, Cr, Co, and Cu in skeletons of 15 species of birds of prey from Eastern Poland were presented. The greatest amounts of 137Cs and 90Sr (70 Bq/kg and 33 Bq/kg, respectively) were found in rough-legged buzzards (Buteo lagopus), winter visitors, coming from former soviet nuclear test places. Concentrations of 239+240Pu in raptors were negligible, only lesser-spotted eagles (Aquila pomarina) revealed slightly higher values. Median concentrations of 137Cs and 90Sr in raptors which feed predominantly on small mammals were higher in comparison to concentrations found in other ones preferring different trophy. The most noticeable was a very high lead concentration (reaching above 600 mg/kg) in birds which utilize un-retrieved hunting casualties as their prey.

Fugler i Norge i 2005 - Rapport fra Norsk faunakomité for fugl (NFKF)

THE NORWEGIAN BIRD REPORT 2005 - a report on locally uncommon and scarce birds in Norway in 2005, by the Norwegian Birds Records Committee (NFKF) The basis of this report is the annual reports produced by the county rarities committees. For 2005 all the counties on the mainland contributed to the report, although Finnmark, Troms, Sogn & Fjordane, Rogaland and Vest-Agder counties did not publish own county reports. Svalbard archipelago and Jan Mayen did not contribute to this report. We believe this report reflects fairly well observations from Norway in 2005. Readers should take care to note the geographical or time delimitation of the records stated for the different species, as stated in codes immediately after the scientific name of the species. The Norwegian Birds Records Committee (NFKF) has been publishing annual reports since 1991. The occurrence of Bewick’s Swan Cygnus columbianus was the poorest in NFKFs history, and the occurence of Lesser White-fronted Geese Anser erythropus at the traditional feeding and roosting site at Valdakmyra, Porsanger (FI) continued to be very low. White-fronted Geese Anser albifrons were seen in poor numbers, while Bar-headed Geese Anser indicus were seen in record high numbers. Mandarin Ducks Aix galericulata occurred in high numbers. Gadwalls Anas strepera have occurred in steadily increasing numbers in Norway in recent years, and 2005 was the best year to date for this species. Garganeys Anas qurquedula had a poor year. Quail Coturnix coturnix occurred in good numbers for the fourth year in succession. Yellow-billed Divers Gavia adamsii experienced the second best year since 1991. Due to favourable weather conditions in late August both Sooty Shearwaters Puffinus griseus and Manx Shearwaters Puffinus puffinus occurred in record high numbers. Many Rough-legged Buzzards Buteo lagopus were seen during the winter months. The Eurasian Hobby Falco subbuteo is a raptor that has occurred in high numbers in recent years, and 2005 was the third best year ever. The occurrence of Avocets Recurvirostra avosetta was very poor. Several shorebirds, such as Ringed Plover Charadrius hiaticula, Northern Lapwings Vanellus vanellus, Sanderlings Calidris alba and Bar-tailed Godwits Limosa lapponica were reported in high numbers from mid-January following the winter storm «Inga». The number of migrating Broad-billed Sandpipers Limicola falcinellus, Black-tailed Godwits Limosa limosa and Red-necked Phalaropes Phalaropus lobatus were the second best in NFKFs history. Migrating Pomarine Skuas Stercorarius pomarinus was seen in good numbers. Iceland Gulls Larus glaucoides occurred in record high numbers while the occurrence of Little Gulls Larus minutus and Glaucous Gulls Larus hyperboreus was the third best in NFKFs history. The occurrence of Black Terns Chlidonias niger was very poor. Wood Larks Lullula arborea occurred in record high numbers. The negative trend related to migrating Horned Larks Eremophila alpestris continued in 2005 and the last six years represent the six poorest years for this species. Red-throated Pipits Anthus cervinus had another poor year, while Richard’s Pipits Anthus richardi occured in record high numbers. The occurrence of Yellow Wagtails Motacilla flava flavissima was the poorest in NFKF’s history. Stonechats Saxicola torquata occurred in record high numbers and seventeen confirmed breeding pairs were recorded from coastal areas. The Mistle Thrush Turdus viscivorus is probably expanding significantly in the north of its distribution range. The number of singing Common Grasshopper Warblers Locustella naevia and the occurrence of Yellow-browed Warblers Phylloscopus inornatus was the best ever recorded. The number of Barred Warblers Sylvia nisoria was the second best in NFKF’s history. The number of Great Grey Shrikes Lanius excubitor was the highest ever recorded. Two-barred Crossbills Loxia leucoptera and Pine Grosbeaks Pinicola enucleator occurred in poor numbers. The Ortolan Bunting Emberiza hortulana still has a negative trend and is disappearing from former breeding areas. The Rustic Bunting Emberiza rustica experienced the poorest year in NFKFs history, while the occurrence of Little Buntings Emberiza pusilla was the best ever recorded.

Fugler i Norge i 2006 - Rapport fra Norsk faunakomité for fugl (NFKF)

THE NORWEGIAN BIRD REPORT 2006 -  a report on locally uncommon and scarce birds in Norway in 2006, by the Norwegian Birds Records Committee (NFKF) The basis of this report is the annual reports produced by the county rarities committees. For 2006 all the counties on the mainland are represented in the report, although Finnmark, Troms, Sogn & Fjordane, Rogaland, Vest-Agder and Oppland counties did not publish own county reports. Svalbard archipelago and Jan Mayen did not contribute to this report. We believe this report reflects fairly well observations from Norway in 2006. Readers should take care to note the geographical or time delimitation of the records stated for the different species, as stated in codes immediately after the scientific name of the species. Letters in the tables stated in the beginning of the review of the different species should not be cited as real occurrences. The Norwegian Birds Records Committee (NFKF) has been publishing annual reports since 1991. The occurrence of Bewick’s Swan Cygnus columbianus was the poorest in NFKFs history, and the occurence of Lesser White-fronted Geese Anser erythropus at the traditional feeding and roosting site Valdakmyra, Porsanger (FI) continued to be very low. Bean Geese Anser fabalis had a record high occurrence while Bar-headed Geese Anser indicus had the third best occurrence since 1991. Record high numbers of Dark-bellied Brent Geese Branta bernicla bernicla were observed in southern parts of the Norway during the autumn. Gadwall Anas strepera have occurred in steadily increasing numbers in Norway in recent years, and 2006 was the third best year to date for this species. Garganey Anas quequedula occurred in record high number, while the occurrence of Smew Mergellus albellus was the second best since 1991. Quail Coturnix coturnix occurred in good numbers for the fifth year in succession. Yellow-billed Diver Gavia adamsii experienced the third best year since 1991. Many Rough-legged Buzzards Buteo lagopus were seen during the winter months. The Eurasian Hobby Falco subbuteo is a raptor that has occurred in high numbers in recent years, and 2006 was the best year ever. The occurrence of Corncrakes Crex crex wasthe poorest since 1998 and the occurrence of Avocets Recurvirostra avosetta was the second poorest since 1991. Jack Snipes Lymnocryptes minima were recorded in record high numbers during January to March and the number of spring migrating Great Snipes Gallinago media were record high. The occurrence of Little Gulls Larus minutus reached record high numbers while the occurrence of Sandwich Terns Sterna sandvicensis was very poor. In northern parts of its distribution range many Stock Doves Columba oenas were observed in 2006. Wood Larks Lullula arborea occurred in second best numbers since 1991. The negative trend relatedto migrating Horned Larks Eremophila alpestris was broken in 2006 and this year was the third best since 1991. Stonechats Saxicola torquata occurred in good numbers and eleven confirmed breeding pairs were recorded from the coastal areas of Sogn og Fjordane county. The number of singing Common Grasshopper Warblers Locustella naevia and Marsh Warblers Acrocephalus palustris was the third best since 1991. The occurrence of Yellow-browed Warblers Phylloscopus inornatus was the best ever recorded. The number of Golden Orioles Oriolus oriolus was very poor. The occurrence of Arctic Redpolls Carduelis hornemanni was the third best since 1991, and in late autumn a major influx of Pine Grosbeaks Pinicola enucleator took place in many parts of southern Norway. Many Lapland Buntings Calcarius lapponicus were observed during the winter months. The number of Ortolan Bunting Emberiza hortulana continued to drop and Rustic Bunting Emberiza rustica was observed in record low numbers.

FIRST KNOWN SPECIMEN OF A HYBRID BUTEO: SWAINSON'S HAWK (BUTEO SWAINSONI) × ROUGH-LEGGED HAWK (B. LAGOPUS) FROM LOUISIANA

Abstract We report a specimen that appears to be a hybrid between Swainson's Hawk (Buteo swainsoni) and Rough-legged Hawk (B. lagopus), which, to our knowledge, is the first hybrid specimen for the genus. There are few reports of hybridization between Buteo species, most of which have been observations of interspecific nesting pairs. The specimen described herein was collected in Louisiana and initially identified as a Rough-legged Hawk because of its feathered tarsi and the dark bellyband and carpals. A DNA sequence from the maternally inherited mitochondrial ND6 gene was identical to a published sequence for Swainson's Hawk. Nuclear DNA sequences from two introns contained only five variable sites among a panel of five potential parental taxa, but the hybrid sequence was most consistent with parentage by Rough-legged and Swainson's hawks. The feathered tarsi of the hybrid strongly suggested that the father was either a Rough-legged or Ferruginous hawk (B. regalis), the only North American raptors other ...

Habitat Associations and Population Trends of Two Hawks in an Urbanizing Grassland Region in Colorado

Despite increasing interest in the ecological effects of urbanization, relatively little is known about its effects in grasslands. We examined population trends and habitat associations of two predators, the rough-legged hawk (Buteo lagopus) and the red-tailed hawk (B. jamaicensis), in a rapidly urbanizing grassland region at the western edge of the North American Great Plains. Count data indicate that rough-legged hawk populations declined in the area by nearly 75% between 1971 and 2003, at the same time that numbers of red-tailed hawks more than tripled. These changes were not part of wider regional trends, nor were they buffered by development of an open space system in one of the urbanizing counties. While the human population grew steadily over the 33-year period, hawk numbers did not begin to change significantly until the early 1980s, suggesting landscape threshold responses to development. Rough-legged hawks remaining in the area between 1999 and 2002 avoided human settlements and hunted in places with tracts of treeless grassland. In contrast, red-tailed hawks selected relatively tall perches in trees or on utility poles from which to hunt, in areas closer to buildings and roads than randomly selected plots, and remained abundant in the mosaic of developed and rural agricultural lands. The failure of the grassland open space system to sustain the rough-legged hawk, and other bird species characteristic of treeless open prairie, illustrates the challenges of conserving fauna with apparent hypersensitivity to the three-dimensional habitat complexity that accompanies even modest amounts of development.

Basic II and Basic III plumages of Rough-legged Hawks

Abstract Adult Rough-legged Hawks (Buteo lagopus) are depicted and described in bird guides and handbooks as sexually dimorphic in plumage. We describe for the first time a Basic II plumage for this species, determined by incomplete flight feather molt, in which both sexes have the characters of adult females, and Basic III plumages that are essentially adult by sex but show pale primary patches on the upper wings.

Large‐scale spatial dynamics of vole populations in Finland revealed by the breeding success of vole‐eating avian predators

Summary Voles in northern Europe have been shown to exhibit cyclic population dynamics, with a latitudinal gradient in cycle length, amplitude and interspecific synchrony. Previous studies have been based on a relatively sparse network of sampling sites. In the absence of spatially comprehensive long‐term records of vole dynamics, we analysed a proxy of vole density, bird‐ringing data on vole‐eating avian predators, Tengmalm's owl (Aegolius funereus L.), the Ural owl (Strix uralensis Pall.), the long‐eared owl (Asio otus L.) and the rough‐legged buzzard (Buteo lagopus Pontoppidan) to study spatial population dynamics of voles. We demonstrate that the breeding success of the avian predators is highly dependent on the abundance of voles, which is also reflected in the numbers of nestlings ringed in a particular area in each year. Our results show the expected increase in cycle length from south to north in Finland, but also from west to east, and in contrast to previous studies, increasing irregularity of the cyclic dynamics towards the north. Fluctuations of vole populations have been synchronous over large distances, up to several hundred kilometres. Such large‐scale synchrony is more likely to be caused by movements of vole‐eating predators and/or by climatic perturbations than by dispersal of voles. We could not conclusively verify the recent suggestion that vole population dynamics have become less regular across Finland, although certain long‐term changes are apparent.

Constrained by available raptor hosts and islands: density‐dependent reproductive success in red‐breasted geese

In this paper we aim to explain the distribution of red‐breasted geese Branta ruficollis over different nesting habitats. To be safe from land predators red‐breasted goose colonies were restricted to i) islands on rivers, ii) cliffs with peregrine falcons Falco peregrinus, and iii) the close proximity of snowy owl Nyctea scandiaca and rough‐legged buzzard Buteo lagopus nests. Among years nest site availability varied by fluctuations in numbers of owls and buzzards in association with cycles in lemming abundance, but the total number of goose nests found in the study area did not vary. The distribution of geese, in combination with data on reproductive success, suggested a despotic mechanism: at cliffs, goose numbers were constant among years with an invariably high reproductive success, whereas large fluctuations in numbers on islands coincided with opposite trends in success. Apparently, geese nesting with owls or buzzards moved to the few islands present in the study area during years when these birds of prey were absent. Consequently, in such years the average density of geese on islands was more than twice as high as at cliff colonies (5.4 and 2.3 pairs per ha of foraging habitat, respectively). Colony size at cliffs may have been restricted by territorial behaviour of the geese, though there is evidence that, additionally, the host falcons also limited the number of nesting geese. Apparently rare in closely related species, we observed a negative density‐dependent effect on reproductive success during the nest phase, and attribute this to limited food resources, reinforced by the high frequency of territorial interactions. This leads to the conclusion that, in addition to predation pressure, nesting density is an important agent in the link between lemming cycles and goose breeding success.

Predator protection or similar habitat selection in red-breasted goose nesting associations: extremes along a continuum

We tested the predator protection and similar habitat hypotheses in relation to red-breasted goose,Branta ruficollis , nesting associations. Geese began laying 1–3 weeks after all associated species. In almost all cases they nested on the mainland only if raptors were also present and always followed raptors when they changed eyries between years. They selected peregrines, Falco peregrinus, and snowy owls, Nyctea scandiaca, as associates in preference to rough-legged buzzards, Buteo lagopus, even though the latter were several times more abundant along river corridors. Nest defence experiments with a surrogate Arctic fox, Alopex lagopus, showed that this could be explained by differences in nest defence intensity, rather than habitat types selected. Similar experiments also suggested that gulls were much less aggressive than owls or falcons. Foxes rarely approached, and were easily repelled from goose colonies associated with owls and peregrines, but gulls were apparently incapable of repelling foxes. Breeding success was much higher for geese nesting with raptors than for those on islands and geese apparently preferred to nest with owls in peak lemming years than to remain on islands. These findings support the hypothesis that red-breasted geese actively choose to nest near raptors; however, they probably associate with gulls primarily because both species select fox-free islands. Compared with other studies, red-breasted geese nesting with raptors and on islands apparently represent two extremes in a continuum of nesting associations generally seen in birds. We discuss why the behaviour might have evolved and argue that this may be the only known bird species whose evolution has been facilitated primarily by the exploitation of the nest defence behaviour of aggressive raptorial hosts. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Population trends in Swedish raptors demonstrated by migration counts at Falsterbo, Sweden 1942–97

The autumn migration of raptors at Falsterbo, Sweden has been studied since the early 1940s, and from 1973 standardized counts were made. Here we present data for 15 species over a 39-year period from 1942–97. These are discussed in the context of available information on population trends in Sweden and neighbouring countries. Although annual numbers and concentration rate vary considerably between species, population changes are very well reflected in the migration figures from Falsterbo. Most raptors showed stable populations at a fairly high level during the 1940s, but a marked decline was already obvious in White-tailed Eagle Haliaeetus albicilla and Peregrine Falcon Falco peregrinus. During the 1950s and 1960s, a more or less steep decline occurred in most species. Four species started to increase during the 1960s, but the real change came during the 1970s. At that time, decreased human persecution and a reduction in the effects from pesticides resulted in a general increase in Scandinavian raptors, with only Honey Buzzard Pernis apivorus continuing to decrease. The increases continued during the 1980s, but in the 1990s many raptors seem to have reached stable numbers or to have started to decline again. Two species, Marsh Harrier Circus aeruginosus and Montagu's Harrier C. pygargus show a positive trend through the study period. Numbers of Northern Harrier Circus cyaneus, Rough-legged Buzzard Buteo lagopus and Eurasian Kestrel Falco tinnunculus stabilized during the 1980s and show a clear decline since then, most probably due to a general lack of rodent peaks in Northern Scandinavia since 1982. Most species of raptors seem to be doing reasonably well at the moment, but a continuous decline in Honey Buzzard and Common Buzzard Buteo buteo is disturbing, and is possibly due to declining proportions of old deciduous forest and grazed meadows in Scandinavia. Since a general census programme of birds of prey does not exist in Sweden, the migration counts at Falsterbo is the best general method of monitoring population changes.

Rough-Legged Buzzards Use Vole Scent Marks to Assess Hunting Areas

Voles scent mark their territories with urine and faeces that are visible in ultraviolet (UV) light. Rough-legged Buzzards Buteo lagopus feed mainly on voles. We performed a field experiment in northern Finland to test whether buzzards are attracted to UV-visible vole scent marks. The buzzards hunted more often on plots with vole scent marks than on control plots. Our results indicate that Rough-legged Buzzards may be able to use vole scent marks as a cue when searching for profitable hunting and breeding areas.

Annual variation in numbers, age and sex ratios among migrating raptors at Falsterbo, Sweden from 1986–1995

The annual variation in age and sex ratio among raptors passing the Falsterbo peninsula, Sweden was studied the ten autumns 1986–1995. The analysis encompasses thirteen species with average annual totals of between 25 and 14,000 migrants. In general, raptors occurring in low numbers showed the greatest relative annual variation. One explanation for high variation was the steep increase in the Swedish populations of Red KiteMilvus milvus and Marsh HarrierCircus aeruginosus during the period. A constant high percentage of juveniles may be due to the adults being primarily residents, like in Red Kite and GoshawkAccipiter gentilis, or to a less pronounced tendency of adults to follow leading lines, as in Marsh Harrier, MerlinFalco columbarius and HobbyF. subbuteo. In most other species the ages were represented in more balanced proportions, and the proportion of juveniles most likely reflects variations in breeding results. An average of 41% juveniles in Common BuzzardButeo buteo compared to 23% in the Rough-legged BuzzardB. lagopus indicates a considerably better production in the first species during the ten years. The extremely low average of 11% young Honey BuzzardsPernis apivorus most likely represents a very low production in the period. There was a highly significant correlation in the annual proportion of juveniles between Northern HarrierCircus cyaneus and Rough-legged Buzzard. Most likely this covariation reflects fluctuation in rodent numbers in northern Scandinavia. Most species showed a sex ratio close to 50%. In both Northern and Marsh Harrier there was however a clear dominance of females among the adults, with a ratio of 1.63 and 1.27 females/male respectively.