Rough-Legged Buzzards, Arctic Foxes and Red Foxes in a Tundra Ecosystem without Rodents

Abstract

Small rodents with multi-annual population cycles strongly influence the dynamics of food webs, and in particular predator-prey interactions, across most of the tundra biome. Rodents are however absent from some arctic islands, and studies on performance of arctic predators under such circumstances may be very instructive since rodent cycles have been predicted to collapse in a warming Arctic. Here we document for the first time how three normally rodent-dependent predator species—rough-legged buzzard, arctic fox and red fox – perform in a low-arctic ecosystem with no rodents. During six years (in 2006-2008 and 2011-2013) we studied diet and breeding performance of these predators in the rodent-free Kolguev Island in Arctic Russia. The rough-legged buzzards, previously known to be a small rodent specialist, have only during the last two decades become established on Kolguev Island. The buzzards successfully breed on the island at stable low density, but with high productivity based on goslings and willow ptarmigan as their main prey – altogether representing a novel ecological situation for this species. Breeding density of arctic fox varied from year to year, but with stable productivity based on mainly geese as prey. The density dynamic of the arctic fox appeared to be correlated with the date of spring arrival of the geese. Red foxes breed regularly on the island but in very low numbers that appear to have been unchanged over a long period – a situation that resemble what has been recently documented from Arctic America. Our study suggests that the three predators found breeding on Kolguev Island possess capacities for shifting to changing circumstances in low-arctic ecosystem as long as other small - medium sized terrestrial herbivores are present in good numbers.

Flexibility in a changing arctic food web: Can rough‐legged buzzards cope with changing small rodent communities?

“…In that population, mean clutch size and mean brood size were also higher with 4.4 and 4.0, respectively (Beardsell et al, ), than in southern Yamal (mean clutch size = 3.1 and mean brood size = 1.3). In populations relying partly or completely on other prey than small rodents, both densities and clutch/brood size were lower and similar to the ones observed at Erkuta after 2005 (Pokrovsky et al, , ). Particularly high breeding densities have been reported from Fennoscandia, where buzzards reached 25 pairs per 100 km 2 in peak small rodent years (Hellström et al, ).…”

“…In northern Fennoscandia, they are small rodent specialists (Tast et al, ), with a preference for Norwegian lemmings as prey (Hellström et al, ). In other areas, however, they are less specialized and use birds, notably ptarmigan, as alternative prey in low small rodent years (Pokrovsky et al, ; Springer, ), or breed even in areas where small rodents are absent, such as on Kolguev Island (Pokrovsky et al, ). None of these studies documented; however, the reaction of a buzzard population to a change in resource availability over time, and it was therefore unclear how fast they could adapt to such changes locally.…”

“…and Branta spp.) are the main prey during the breeding period in addition to willow ptarmigan (Kondratyev & Zaynagutdinova, ; Pokrovsky et al, ). It is at present not clear whether these buzzards belong to distinct populations having adapted to use these alternative resources, or whether the species is in general quite resilient to changes in available prey.…”

Family size dynamics in wintering geese

“…Juvenile summertime survival of Arctic-breeding birds including geese has earlier been strongly linked to the cyclical abundance of and concomitant levels of predation on Arctic rodents Arvicolinae in the 'alternative prey hypothesis' (Summers and Underhill 1987). However, Kolguev Island lacks lemmings and their associated cycle (Kondratyev and Zaynagutdinova 2008;Kruckenberg et al 2008), and young geese form the regular, main prey of most predators there (Pokrovsky et al 2015). This is shown to result in strong family size decreases between hatching (early July; mean ≈ 3) and fledging (end July; mean ≈ 2; see Kondratyev and Zaynagutdinova 2008).…”

Adaptability of a specialist predator: the effects of land use on diet diversification and breeding performance of Verreaux's eagles

“…For example, in Montagu's harriers Circus pygargus diet diversification, as a consequence of reductions of traditional prey resources, has been correlated with lower breeding success (Arroyo and Garcia 2006). However, responses are variable and important factors to consider are the level of intensification of land use and the ability for individual plasticity to occur within the species of concern (Pokrovsky et al 2015). The classification of generalist or specialist can occur along a gradient of adaptability and furthermore, a generalist species can be made up of specialized individuals (Bolnick et al 2003).…”