Density-dependent increase in superpredation linked to food limitation in a recovering population of northern goshawks Accipiter gentilis

S. R Hoy (1) , S. J Petty (1) , A. Millon (2) , D. P Whitfield , M. Marquiss (1) , D. I. K. Anderson , M. Davison , X. Lambin (1)

1 School of Biological Sciences [Aberdeen]
2 IMBE - Institut méditerranéen de biodiversité et d'écologie marine et continentale

A better understanding of the mechanisms driving superpredation, the killing of smaller mesopredators by larger apex predators, is important because of the crucial role superpredation can play in structuring communities and because it often involves species of conservation concern. Here we document how the extent of superpredation has changed over time, and assessed the impact of such temporal variation on local mesopredator populations using 40 yr of dietary data collected from a recovering population of northern goshawks Accipiter gentilis, an archetypical avian superpredator. We then assessed which mechanisms were driving variation in superpredation, e.g. was it opportunistic, a response to food becoming limited (due to declines in preferred prey) or to reduce competition. Raptors comprised 8% of goshawk diet on average in years when goshawk abundance was high, which is higher than reported elsewhere. Additionally, there was a per capita increase in superpredation as goshawks recovered, with the proportion of goshawk diet comprising raptors increasing from 2 to 8% as the number of goshawk home‐ranges increased from ≤ 14 to ≥ 25. This increase in superpredation coincided with a population decline in the most commonly killed mesopredator, the Eurasian kestrel Falco tinnunculus, which may represent the reversal of the ‘mesopredator release’ process (i.e. mesopredator suppression) which occurred after goshawks and other large raptors declined or were extirpated. Food limitation was the most likely driver of superpredation in this system given: 1) the substantial decline of two main prey groups in goshawk diet, the increase in diet diversity and decrease in goshawk reproductive success are all consistent with the goshawk population becoming food‐limited; 2) it's unlikely to be purely opportunistic as the increase in superpredation did not reflect changes in the availability of mesopredator species; and 3) the majority of mesopredators killed by goshawks do not compete with goshawks for food or nest sites.

Mots clés: mesopredator; predatory interactions; falco tinnunculus; mesopredator suppression; intraguild predation; food-stress hypothesis

Domaines: Zoologie des vertébrés; Interactions entre organismes; Biodiversité et Ecologie; Interfaces continentales, environnement; Sciences de la Terre

S. R Hoy, S. J Petty, A. Millon, D. P Whitfield, M. Marquiss, et al.. Density-dependent increase in superpredation linked to food limitation in a recovering population of northern goshawks Accipiter gentilis. Journal of Avian Biology, 2017, 48 (9), pp.1205-1215. ⟨10.1111/jav.01387⟩. ⟨hal-01768454⟩