Gyrfalcon Falco Rusticolus Research Articles

Is hunting mortality additive or compensatory to natural mortality? Effects of experimental harvest on the survival and cause-specific mortality of willow ptarmigan

1. The effects of harvest on the annual and seasonal survival of willow ptarmigan Lagopus lagopus L. were tested in a large-scale harvest experiment. Management units were randomly assigned to one of three experimental treatments: 0%, 15% or 30% harvest. Seasonal quotas were based on the experimental treatment and estimates of bird density before the hunting season. Survival rates and hazard functions for radio-marked ptarmigan were then estimated under the competing risks of harvest and natural mortality. 2. The partially compensatory mortality hypothesis was supported: annual survival of ptarmigan was 0·54 ± 0·08 SE under 0% harvest, 0·47 ± 0·06 under 15% harvest, and was reduced to 0·30 ± 0·05 under 30% harvest. Harvest mortality increased linearly from 0·08 ± 0·05, 0·27 ± 0·05 and 0·42 ± 0·06 from 0% to 30% harvest, whereas natural mortality was 0·38 ± 0·08, 0·25 ± 0·05 and 0·28 ± 0·06 under the same treatments. 3. Realized risk of harvest mortality was 0·08-0·12 points higher than our set harvest treatments of 0-30% because birds were exposed to risk if they moved out of protected areas. The superadditive hypothesis was supported because birds in the 30% harvest treatment had higher natural mortality during winter after the hunting season. 4. Natural mortality was mainly because of raptor predation, with two seasonal peaks in fall and spring. Natural and harvest mortality coincided during early autumn with little potential for compensation during winter months. Peak risk of harvest mortality was 5× higher than natural mortality. Low natural mortality during winter suggests that most late season harvest would be additive mortality. 5. Environmental correlates of natural mortality of ptarmigan included seasonal changes in snow cover, onset of juvenile dispersal, and periods of territorial activity. Natural mortality of ptarmigan was highest during autumn movements and nesting by gyrfalcons Falco rusticolus L. Mortality was low when gyrfalcons had departed for coastal wintering sites, and during summer when ptarmigan were attending nests and broods. 6. Our experimental results have important implications for harvest management of upland gamebirds. Seasonal quotas based on proportional harvest were effective and should be set at ≤ 15% of August populations for regional management plans. Under threshold harvest of a reproductive surplus, 15% harvest would be sustainable at productivity rates ≥ 2·5 young per pair. Impacts of winter harvest could be minimized by closing the hunting season in early November or by reducing late season quotas.

Archaeology among the bird droppings: what does it tell us about raptor nest‐site selection?

Some fascinating questions are raised by Kurt and William Burnham and Ian Newton's findings, reported in this issue of Ibis, that 14C dating has shown some Gyrfalcon Falco rusticolus nests to have been occupied for around the past 2500 years. As the authors demonstrate, this finding could make an important contribution to our understanding of climate change in the high arctic. And stable isotope analysis also has the potential to record changes in prey selection and foraging habitat over long periods of time. Other detritus from nest-sites can also achieve this.

A Bird’s-Eye View of Arctic Governance: Reflecting on the Role of International Law in Arctic Cooperation from a Bird Conservation Perspective

Abstract This article discusses the role of international law in environmental governance in the Arctic. It does so from the perspective of bird conservation. Challenges in the latter field are introduced, including the impact of climate change on Arctic bird habitats and the incidental mortality of seabirds in Arctic fisheries. The ability of the current international legal framework in the Arctic to meet these challenges is scrutinised, and future scenarios for its enhancement are explored, including the conclusion of (a) new legally binding agreement(s). Five species receive particular attention as part of this exercise: gyrfalcon (Falco rusticolus), ivory gull (Pagophila eburnea), spoon-billed sandpiper (Eurynorhynchus pygmeus), Kittlitz’s murrelet (Brachyramphus brevirostris) and Brünnich’s guillemot (Uria lomvia). Special attention is also devoted to the issue of seabird bycatch.

MOLTED-FEATHER PERSISTENCE AND AGING IN A SUB-ARCTIC ENVIRONMENT: IMPLICATIONS FOR NONINVASIVE GENETIC SAMPLING

Abstract We investigated molted-feather persistence and aging in a sub-Arctic environment by placing marked feathers at historical Gyrfalcon (Falco rusticolus) nesting areas and returning a year later to collect and inspect remaining feathers. After one year, only 14% of marked feathers remained and were collected during primary searches; small, body feathers were significantly less likely to persist than large or flight feathers. No differences in trends were detected between feathers from perch and below-nest locations. All recovered feathers displayed at least one of three signs of aging (matted and separated barbs, fungal growth, or algal growth) that reliably distinguished them from fresh feathers. We show that collection efforts should focus on small, body feathers to ensure that collected feathers are freshly molted and suggest feather persistence and aging be directly addressed in other studies using feathers for noninvasive genetic sampling. Doing so should reduce potential genotyping and data in...

Territory occupancy rate of goshawk and gyrfalcon: no evidence of delayed numerical response to grouse numbers

Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2-3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern Norway, however, subadult (two-year-old) goshawk hens occupied only 18-25% of territories where occupancy was not recorded in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather (most important for the gyrfalcon) should also be addressed. During 1988-2006, the annual proportion of goshawk territories with recorded nesting attempts in southern Norway was most closely related to the preceding autumn's population indices of black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse cycles.

Effect of local prey availability on gyrfalcon diet: DNA analysis on ptarmigan remains at nest sites

AbstractThe aim of this study was to investigate how the diet of gyrfalcon Falco rusticolus in northern Sweden was affected by the relative availability of its two main prey species: rock ptarmigan Lagopus mutus and willow ptarmigan Lagopus lagopus. In order to do so, we needed a method to estimate the gyrfalcon's diet proportions of rock and willow ptarmigan from prey remains that we collected from nest sites in separate breeding territories. We also needed a method to calculate the availability of the two prey species in the same breeding territories that the prey remains originated from. We could then compare the diet proportions with prey availability and investigate if the gyrfalcons utilized the two species strictly in relation to their densities, or if they showed a preference for any of the prey species. Morphometric identification to species level from ptarmigan remains was not possible. Therefore, we developed a PCR‐based process of DNA analysis, which could be applied on any ptarmigan bone or bone remains. This method allowed us to establish the ratio of rock and willow ptarmigan in gyrfalcon diets that originated from single gyrfalcon breeding occasions. The relative availability of the two ptarmigan species in gyrfalcon breeding territories was calculated with a GIS model that incorporated observations on ptarmigan habitat preferences. The DNA identification was performed on 176 ptarmigan bones from 13 different breeding occasions occurring in five different territories. The results indicated that the two ptarmigan species comprised at least 93% of the average gyrfalcon diet, and that rock ptarmigan was the most common prey during all 13 breeding occasions. There was a positive relationship between the relative amount of rock ptarmigan in the diet and the proportion of rock ptarmigan habitat in the territories; hence, the gyrfalcons ptarmigan utilization seemed to be density dependent. However, rock ptarmigan was found to be overrepresented in the diet, which may reflect a preference for rock ptarmigan over willow ptarmigan. The conservation implications of these findings in relation to ptarmigan hunting are discussed.

Gyr Falcons, ptarmigan and microtine rodents in northern Sweden

A Gyr Falcon Falco rusticolus population in Northern Sweden (66°N, 17°E) was monitored from 1996 to 2002 in relation to its predator–prey interactions with its main and alternative prey species. Ptarmigan species Lagopus spp., and especially Rock Ptarmigan L. mutus, were the Gyr Falcons’ most important prey and constituted more than 90% of the prey biomass. A 21‐fold difference in ptarmigan abundance was found across Falcon breeding territories. However, this great variation in prey availability corresponded to only about a 10% shift in Gyr Falcon diet across territories, suggesting that the Falcons were reluctant or unable to compensate for declining ptarmigan availability by using alternative prey categories. Gyr Falcons did not respond functionally to microtine rodent abundance. Their diets were unaffected by a peak in the microtine rodent population cycle when Norwegian Lemmings Lemmus lemmus occurred in high numbers in the study area. Gyr Falcons responded numerically to their prey in two ways. First, there was a reproductive response with a significant relationship between the number of chicks fledged and the number of ptarmigan in the breeding territories. Secondly, although the Gyr Falcons did not utilize microtines as prey, there was a relationship between the microtine rodent abundance and the number of pairs that attempted to breed each year. This could be a result of an indirect community interaction, assuming that other predators switched from ptarmigan to microtines as prey, which could have had a positive effect on the breeding performance of the Gyr Falcons. The Gyr Falcons acted as true specialist predators, and their narrow food niche probably reflected a general lack of suitable alternative prey in the study area.

Temporal trends of organochlorine contamination in Black Guillemots in Iceland from 1976 to 1996

The levels of several different persistent organochlorines (OCs) in Black Guillemots Cepphus grylle, collected during the summers of 1976–1996 at Breiðafjörður in W-Iceland, were investigated. The levels of about 40 different organochlorines (PCBs, DDTs, chlordanes, toxaphenes, HCH, HCB) were compared with respect to age, sex, fat content, and year of collection. The levels of PCBs correlated very closely with those of DDE, indicating long-range transport as the major source of these contaminants in Iceland, with the ratio PCBs/DDE mostly in the range of 2–5. Unlike the Gyrfalcon Falco rusticolus, the organochlorine levels did not seem to accumulate substantially with age, neither in males nor females. The variation in the levels of OCs at the age of 2 years was even greater than the variation in OC levels over an age range of 12 years. In immature birds the levels of PCBs, DDE, HCB and β-HCH declined very slowly ( T 1/2 from 12 to 20 years) over the years 1976–1996, whereas the levels of α-HCH and p, p′-DDT declined much faster. The levels of trans-nonachlor, α-chlordane, γ-chlordane, oxychlordane, and toxaphene did not correlate with the year of collection. As the Black Guillemot is mostly a resident seabird, feeding mainly on small fish and invertebrates, this investigation should give a good indication of the temporal trends of organochlorine pollution at Breiðafjörður, Iceland, during this 20 year period and is likely to reflect baseline trends in the marine environment of the North-Atlantic Ocean.

Fragmentation and preservation of bird bones in uneaten food remains of the Gyrfalcon Falco rusticolus

This paper presents fragmentation patterns of bird bones in uneaten food remains of the gyrfalcon Falco rusticolus. The victims' bones show a relatively low degree of fragmentation. Elements of the pectoral girdle and wing predominate while head and leg elements are poorly represented.

GYRFALCON DIET IN CENTRAL WEST GREENLAND DURING THE NESTING PERIOD

Abstract We studied food habits of Gyrfalcons (Falco rusticolus) nesting in central west Greenland in 2000 and 2001 using three sources of data: time-lapse video (3 nests), prey remains (22 nests), and regurgitated pellets (19 nests). These sources provided different information describing the diet during the nesting period. Gyrfalcons relied heavily on Rock Ptarmigan (Lagopus mutus) and arctic hares (Lepus arcticus). Combined, these species contributed 79–91% of the total diet, depending on the data used. Passerines were the third most important group. Prey less common in the diet included waterfowl, arctic fox pups (Alopex lagopus), shorebirds, gulls, alcids, and falcons. All Rock Ptarmigan were adults, and all but one arctic hare were young of the year. Most passerines were fledglings. We observed two diet shifts, first from a preponderance of ptarmigan to hares in mid-June, and second to passerines in late June. The video-monitored Gyrfalcons consumed 94–110 kg of food per nest during the nestling per...

Persistent organochlorine levels in six prey species of the gyrfalcon Falco rusticolus in Iceland

Our previous investigations have revealed very high levels of organochlorines (OCs) in the Icelandic gyrfalcon Falco rusticolus, a resident top predator. We now examine six potential prey species of birds, both resident and migratory, in order to elucidate the most likely route of the OCs to the gyrfalcon. The ptarmigan Lagopus mutus, the most important prey of the gyrfalcon, contained very low levels of OCs. Bioaccumulation of polychlorinated biphenyls (PCBs) and DDTs in mallards Anas platyrhynchos, tufted ducks Aythya fuligula, golden plovers Pluvialis apricaria, purple sandpipers Calidris maritima, and black guillemots Cepphus grylle reflected their position in the foodchain. The differences in OC-levels seem nevertheless too high just to reflect the different foodchain levels of these species in Iceland. The winter grounds of the migratory golden plovers and tufted ducks appear to be more contaminated than the Icelandic terrestrial habitat of ptarmigans or the freshwater habitat as reflected in mallards, both resident species. However, spending the winter on the coast in Iceland, results in high levels of contaminants in purple sandpipers and black guillemots. Our results indicate OC contamination of the marine ecosystem in Iceland while the terrestrial and freshwater ecosystems are little affected. It is postulated that gyrfalcons receive the major part of the observed contamination from prey other than ptarmigan, especially birds associated with the marine ecosystem and also from migratory birds.

Population fluctuations of gyrfalcon and rock ptarmigan: analysis of export figures from Iceland

We analysed harvest data for gyrfalcon Falco rusticolus and rock ptarmigan Lagopus mutus from Iceland with respect to regularity in fluctuations of numbers. The gyrfalcon data concerned live trapped birds exported to Denmark between 1731 and 1793, and totalled 4,848 falcons, including 4,318 grey, 156 half‐white and 374 white colour morphs. According to contemporary sources grey birds were part of the local breeding population (islandus‐type birds) but the other morphs represented mainly visitors from Greenland. This is also the current situation but some of the lightest Icelandic breeders could be classified as half‐white. The rock ptarmigan harvest data concerned birds exported to Europe in the period 1864–1919, in total ca 3.3 million birds. The data series for white and half‐white gyrfalcons were significantly correlated (r = 0.501, p < 0.001). The data series for grey and white morphs (r = ‐0.099, P = 0.445) and grey and the half‐white morphs (r = ‐0.1183, P = 0.360), showed no correlation. Time series analysis showed that the white (candicans‐type) morph fluctuated irregularly. The half‐white morph behaved similarly but also showed some affinity with the grey morph, and could have represented a mixture of local breeders and Greenlandic winter visitors. Grey morph gyrfalcons and rock ptarmigan showed regular fluctuations in numbers with a 10‐year periodicity. The reliance of Icelandic gyrfalcons on rock ptarmigan during the early part of the breeding season and in all phases of the ptarmigan cycle is well established and may offer a case for causal connections between the two cyclic populations.

Seasonal Changes in Food Habits of Gyrfalcons in NE-Iceland

Food habits of three subpopulations of the Gyrfalcon Falco rusticolus were studied in coastal, lakeland and heathland habitats of NE-Iceland by analysis of 2,316 pellets collected from February 1984-July 1985. No coastal and lakeland Gyrfalcons traveled more than 7.5 km to reach areas with plenty of waterfowl or seabirds (average 3.4 km in winter). Heathland falcons traveled farther to reach equally rich areas for these kinds of prey, e.g. in winter 13-33 km (average 12.9 km). Rock Ptarmigan Lagopus mutus was the main prey for all Gyrfalcons constituting 61% of total pellet volume. Rock Ptarmigan was most important during the early phase of the breeding season (April-June) and in autumn and early winter (August-December). Factors determining high vulnerability in spring seem to be behaviour and coloration of males and in late summer, the large number of naive young. Importance of Rock Ptarmigan on heathland territories as measured by pellet volume ranged from 61-100% for the different collection periods, and 8-85% and 13-91% on coastal and lakeland territories respectively. Other prey groups of importance on heathland territories were waders (max. 12%) in summer and wood mouse Apodemus sylvaticus (max. 20%) and waterfowl (max. 20%) in winter. Lakeland Gyrfalcons increased their take of waterfowl (max. 56%) and waders (max. 13%) in summer and passerines (max. 19%) and wood mice (max. 43%) in winter. Coastal Gyrfalcons had the most variable diet: they increased their take of waterfowl (max. 42%) and waders (max. 21%) in summer and waterfowl (max. 68%) and alcids (max. 38%) in winter. Switching from Rock Ptarmigan to alternate prey involved in most cases a change of hunting habitat, from upland areas to wetland or coastal areas.

Ecology of gyrfalcons, Falco rusticolus, in the central Canadian Arctic: diet and feeding behaviour

Diet and aspects of feeding behaviour in a population of gyrfalcons (Falco rusticolus) in the Northwest Territories were examined between 1984 and 1986. Three prey species, rock ptarmigan (Lagopus mutus), arctic ground squirrel (Spermophilus parryii), and arctic hare (Lepus arcticus), composed 96.5% of total prey biomass identified. Ptarmigan and hares were taken in May and June of all years (98.2% of biomass). Juvenile squirrels were used extensively in July and August of 1984 and 1985 but not in 1986, when squirrel production fell to almost zero; ptarmigan continued to be the dominant prey species throughout that summer. Because densities of breeding ptarmigan remained relatively constant during the study, but those of juvenile ground squirrels did not, it appeared that gyrfalcons responded functionally to varying availability of prey. Mean weight (250 g) of prey taken by male gyrfalcons was significantly less than the weight (330 g) of prey taken by females. As predicted by optimal foraging theory, average size of prey brought to the nest increased as time away from the nest increased. Conditions of food abundance were observed at most nests, suggesting that the amount of food available during the nestling period was not limiting production. We suggest that annual production is a function of spacing of pairs, which is set during courtship and prelaying, when prey availability is at its yearly low and when males must forage for both members of the pair. The fact that most gyrfalcon pairs initiated laying only after the spring arrival of migrating ptarmigan is consistent with this conclusion.

Mercury in feathers of Swedish gyrfalcons, Falco rusticolus, in relation to diet.

The gyrfalcon (Falco rusticolus) is mainly a resident bird breeding in mountain areas in Fennoscandia. The population (estimated to 300-500 pairs) probably fluctuates according to the presence of willow grouse (Lagopus lagopus) and ptarmigan (Lagopus mutus). Little is known about pollutant levels in Fennoscandian gyrfalcons. Previous studies found low levels of DDE, PCB and mercury in organs from six Norwegian gyrfalcons. In this paper the author has included additional information on mercury levels, based on feather analyses from a few nests in northern Sweden. The use of feathers is a simple method to monitor mercury levels without sacrificing the birds. Food habits were checked by analyzing food remains at and near the nests.

Characteristics and Relative Occurrence of Remnants of Prey Found at Nesting Places of Gyrfalcon Falco rusticolus

Characteristics and Relative Occurrence of Remnants of Prey Found at Nesting Places of Gyrfalcon Falco rusticolus

DDE in a Resident Aleutian Island Peregrine Population

The chlorinated hydrocarbons, especially DDT and its derivatives, are responsible for some of the perturbations we are witnessing today in bird populations (Anderson et al. 1969; Porter and Wiemeyer 1969; Heath et al. 1969; Enderson and Berger 1970). In an effort to record the cosmopolitan occurrence of these chemical compounds in the world's ecosystems, biologists have sampled in many remote areas. Continued sampling from specific localities suggests that the chlorinated hydrocarbons are indeed accumulating at top trophic levels in food webs, but that concentrations vary greatly from region to region depending on remoteness from areas of major application of these chemicals and on their patterns of dispersal. The scope of the global contamination by the DDT compounds is indicated by the fact that small amounts are found in the Ad6lie Penguin (Pygoscelis adeliae) and the Skua (Catharacta skua) in Antarctica (Tatton and Ruzicka 1967), and by the small amounts in resident Gyrfalcons (Falco rusticolus) and the dangerously high amounts in migratory Peregrine Falcons (Falco peregrinus) in arctic Alaska (Cade et al. 1971). Because Peregrines are top predators in food webs, preying primarily on birds, they readily accumulate persistent pesticides and are therefore particularly good indicators of the biological magnification of chemicals in an ecosystem. This report presents data on the accumulation of DDE (a major metabolite of DDT) in an essentially resident Peregrine population (White et al. 1971) and their prey, in a relatively remote habitat, Amchitka Island (approx. 510 N and 179' E) in the central North Pacific Ocean. METHODS

Peregrine Falcon Survey, West Greenland, 1972

... The main purpose of the 1972 survey was to study a sample area of West Greenland to supply baseline data about peregrine falcons from which future surveys could determine the status and trends of this bird in Greenland. The main part of the study had as its goals: 1) to determine the density, distribution, and reproductive success of nesting peregrines in a sample area; 2) to band all peregrine nestlings found; 3) to determine prey species of the peregrine; 4) to make interspecific observations of peregrines and gyrfalcons; 5) to make detailed observations from a blind of a sample peregrine falcon eyrie; 6) to conduct a small-bird census in the area of the sample eyrie; 7) to make a photographic record in colour slides and movies of the investigations. ... Eight peregrine falcon eyries and 3 gyrfalcon eyries were found in the survey area. In all, 18 nestlings were found in the 8 peregrine eyries. Of the 8 eyries, 1 had no young, but showed signs of occupancy ... and was defended by an aggressive pair of falcons. Of the other 7 eyries where we found hatched young, 1 had 4 young, 4 had 3 young, and 2 had 1 young bird each. Of the total of 18 nestling peregrines, 13 were banded and 5 were fully-fledged, on the wing, and unable to be caught for banding. Of the peregrine nestlings banded, 9 were males and 4 were females. The number of nestlings (18) in the 8 peregrine eyries gave a production rate of 2.25 per eyrie, or 2.57 if an average is taken of the 7 eyries actually producing young. At 1 eyrie a young falcon was found dead (the eyrie with 4 young). We know that at least 8 of the remaining 17 young fledged successfully, but we are uncertain about the success of the others and cannot therefore make a definite statement on fledging ratio. We estimate, however, that the fledging rate of the peregrines in our survey area was at least 2.00 per producing eyrie. The maximum dimensions of our irregularly-shaped survey area were 39 x 34 miles (63 x 55 km). The estimated area of the survey was about 800 sq. mi. (2,072 sq. km), or about 700 sq. mi. (1,800 sq. km) when the surface area of fiords and lakes is excluded. The nesting density of the active, young-producing peregrine eyries (7) was about 1 pair per 100 sq. mi. (260 sq. km). ... At the 3 gyrfalcon (Falco rusticolus) eyries we found 8 nestlings or fully-fledged young, of which we were able to band 3. Peregrines and gyrfalcons (and a rare white-tailed sea eagle, Haliaetus albicilla) are the only avian predators nesting in southern West Greenland, although ravens (Corvus corax) competed for some nesting cliff sites. We collected remains of prey species and pellets at each falcon eyrie. Addled eggs (2) from 2 peregrine eyries were collected for pesticide analysis. Eggshell fragments for thickness determination were gathered at 5 peregrine eyries. ... Peregrine falcons in West Greenland appear to be in a healthy state as evidenced by a high nesting density (1/100 sq. mi.) and a high production rate (2.25/eyrie), especially in light of the unusually severe conditions in West Greenland during the winter and late spring of 1971-72. We found little interspecific competition for prey species between peregrines and gyrfalcons. The gyrfalcon is already nesting in West Greenland before the peregrines arrive from their winter migration to the south. The gyrfalcons could therefore be expected to be aggressive in defence of their nesting cliffs and thereby occupy optimal cliffs. Despite this, all the peregrines we studied occupied high, sheer, and quite optimal nesting cliffs. Gyrfalcons seemed to prefer a nesting site lower down on a cliff face than peregrines, and both falcons preferred high, sheer cliffs with a southern exposure. Ravens were relegated to lower, less desirable (more accessible) cliffs for nesting. We await pesticide analysis of the peregrine falcon eggs and prey species collected, as well as eggshell thickness determination. Before these facts are determined we can say nothing definite about the status of peregrines in Greenland. Nesting density and production, however, suggest that the status of the peregrine is better in Greenland than in other areas of the north. ...

Banding Gyrfalcons (Falco Rusticolus) in Greenland, 1967

Banding Gyrfalcons (Falco Rusticolus) in Greenland, 1967