Superpredation patterns in four large European raptors

Abstract

Predatory interactions among top predators, like superpredation or intraguild predation (IGP), can influence community structure. Diurnal raptors occupy high trophic levels in terrestrial food webs, and thus can regulate the presence of mesopredators. We studied superpredation (the killing and eating of another predator) in four large European raptors. We gathered 121 dietary studies, totalling 161,456 prey for the Goshawk Accipiter gentilis L., Golden Eagle Aquila chrysaetos L., Bonelli's Eagle Aquila fasciata Vieillot, and Eagle Owl Bubo bubo L. Results showed that superpredation: (1) (2) is not an important energetic resource for large raptors, but rather seems mostly related to diet diversification when the main prey decreases; (3) is spatially clustered reflecting habitat heterogeneity, but shows no temporal or large-scale spatial trends; and (4) it is associated with lower breeding success of the top predator species. These findings support the food stress hypothesis as the main driving force behind increases in superpredation and IGP in raptors, with the decrease in breeding performance as a side effect. Superpredation by large raptors deserves future research to understand its effects on mesopredators, because on one hand it might contribute to promote biodiversity, while on the other hand, it can sometimes represent an additional risk for small populations of endangered mesopredators.

First evidence for carrion–feeding of Eurasian Eagle-owl (Bubo bubo) in Bulgaria

“…The present study corresponds with this assumption (Glutz von Blotzheim & Bauer 1994, Penteriani et al 2005. The level of superpredation as a measure of food stress (Lourenço et al 2011) in years with carrion consumption was lower than the average in the relevant locality.…”

“…The biomass was calculated after Glutz von Blotzheim and Bauer (1994), Popov and Sedefchev (2003). The proportion of predatory mammals and birds in diet formed the value of superpredation, which corresponds positively to the level of food stress (Lourenço et al 2011(Lourenço et al , 2013.…”

“…where p i is the proportion of prey taxon i in the Eurasian Eagle-owl diet (Levins 1968). Larger values of this index indicate a higher dietary diversity.…”

Kill before being killed: an experimental approach supports the predator-removal hypothesis as a determinant of intraguild predation in top predators

“…Some lines of evidence seem to support these hypotheses: the victim is sometimes not consumed (or is only partially eaten); and predatory interactions among top predators are more common when prey is less abundant (competitor-removal hypothesis: Palomares and Caro 1999;Sunde et al 1999) or after prey populations crash (foodstress hypothesis: Korpimäki and Norrdahl 1989;Lourenço et al 2011;Serrano 2000;Tella and Mañosa 1993). However, there are still few empirical evidences supporting these three hypotheses, and to our knowledge the predatorremoval hypothesis has never been tested before (only risks of mutual predation have been so far explored; Palomares and Caro 1999).…”

“…The eagle owl represents a useful biological model for testing IGP hypotheses because: it is a quite well studied superpredator in the context of IGP (Lourenço et al 2011;Sergio et al 2003Sergio et al , 2007; birds of prey show extremely aggressive responses towards eagle owls (Slagsvold 1982;Zuberogoitia et al 2008); and it was recently shown that both the competitor-removal and food-stress hypotheses do not fully explain IGP in this top predator (Lourenço et al 2011). Moreover, eagle owls and diurnal raptors may overlap in space, but show asynchrony in temporal rhythms of activity, which represents a favourable scenario to test the predator-removal hypothesis: eagle owls can easily prey on most diurnal raptors, catching them unaware in the darkness (Mikkola 1976), whereas diurnal raptors attack roosting eagle owls or owlets when they detect them in daylight (authors' observations).…”