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Gyr falcons, ptarmigan and microtine rodents in Northern Sweden
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0001-5535-9086
2005 (English)In: Ibis, ISSN 0019-1019, E-ISSN 1474-919X, Vol. 147, no 3, 587-597 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2005. Vol. 147, no 3, 587-597 p.
National Category
URN: urn:nbn:se:su:diva-23376DOI: 10.1111/j.1474-919x.2005.00436.xOAI: diva2:191637
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2014-10-13Bibliographically approved
In thesis
1. Predator-prey interactions of raptors in an arctic environment
Open this publication in new window or tab >>Predator-prey interactions of raptors in an arctic environment
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns the predator-prey interactions of three raptor species in a Swedish arctic community: the gyrfalcon (Falco rusticolus), the rough-legged buzzard (Buteo lagopus) and the golden eagle (Aquila chrysaetos).

The gyrfalcon behaved like a highly specialised ptarmigan (Lagopus spp.) predator. Gyrfalcon’s functional response to ptarmigan was close to density independent, and ptarmigan remained the dominating prey even in areas with the lowest ptarmigan density. The gyrfalcon did not respond functionally to microtine rodents (i.e. lemmings and voles) and it was clear that the gyrfalcon did not use microtines as an alternative prey category to ptarmigan. As the gyrfalcons did not switch to any alternative prey when ptarmigan was scarce, their reproductive success seemed to be directly dependent on the amount of ptarmigan available in the breeding territories. Of the two ptarmigan species in the study area, rock ptarmigan (L. mutus) dominated gyrfalcon’s diet. Locally, the proportion of rock ptarmigan in gyrfalcons’ diets showed a positive relationship to the expected availability of rock ptarmigan in the breeding territories, indicating a density dependent utilisation.

The rough-legged buzzard behaved like a highly specialised microtine rodent predator and Norwegian lemming (Lemmus lemmus) was its preferred microtine species. The buzzards showed a type 2 functional response to lemmings. Surprisingly though, they also had a type 3 functional response to grey-sided voles (Clethrionomus rufocanus). We present an optimal diet model where a central place forager, during good food conditions, benefits from partial prey preference, which renders separate functional responses to each prey category. We discuss how the double functional responses of the buzzard affect the population dynamics of sympatric vole species, on both temporal and spatial scales.

The golden eagle behaved like a generalist predator, and it preyed on all major prey categories in the study area: microtines, ptarmigan, mountain hare, (Lepus timidus) and reindeer (Rangifer tarandus). It seemed to respond functionally to microtine rodent fluctuations with an increased consumption of lemmings during a peak year in the microtine rodent cycle. The golden eagle showed a numerical response to its main prey, the ptarmigan.

Ptarmigan, microtine rodents and hares seemed to have synchronized population fluctuations in the study area. Such synchronized population fluctuations are believed to be generated by predation. Although the three raptors are the main predators of their community, their predation patterns fail to explain the observed prey population dynamics in the study area.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2004. 32 p.
Ecology of raptors
National Category
urn:nbn:se:su:diva-259 (URN)91-7265-950-5 (ISBN)
Public defence
2004-10-22, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Available from: 2004-10-01 Created: 2004-10-01 Last updated: 2011-11-07Bibliographically approved

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