Foraging strategy of a carnivorous-insectivorous raptor species based on prey size, capturability and nutritional components

Abstract

Optimal foraging theory has typically paid little attention to species feeding on mobile prey and has emphasised energy intake rather than the nutritional contribution of food. The difficulty of capturing food has rarely been included in foraging models, even when it is a potentially important modulator of time devoted to foraging. From the central place foraging and provisioning perspectives, it is posited that at high levels of prey selectivity, the time spent to capture prey is longer than at low levels of prey selectivity. Furthermore, in the case of carnivorous predators, it is thought that nutritional composition does not influence foraging strategies. To explore these issues, we investigated the influence of abundance, size, difficulty of capture, gross energy and nutritional composition (fat, protein, protein-fat ratio and amino acid contents) of prey species on the foraging behaviour of a predator species, the common kestrel Falco tinnunculus, in a region of high diversity of prey species. Our results show that capturability index and load-size explain the foraging behaviour of kestrels. Preferred prey take longer to be provisioned, both selectivity and capturability might explain this result. It is also shown that specific nutritional components, such as protein and amino acid contents, are likely to explain food preference in this carnivorous-insectivorous species.

Reduced ectoparasite load, body mass and blood haemolysis in Eurasian kestrels (Falco tinnunculus) along an urban–rural gradient

“…An increase of soil sealing is linked to lower accessibility of diurnal rodents as suitable prey (Sumasgutner et al, 2014a ; Mitter et al 2015 ) and typically results in a pronounced shift in diet composition towards avian prey (Kübler et al 2005 ; Sumasgutner et al, 2014a , b ). Passerines are poorer in nutritional value compared to voles (Goodwin 1980 ; Kirkwood 1991 ) and kestrels are not necessarily capable of catching agile birds to sufficiently provision offspring with prey items (Fargallo et al 2020 ). The resulting malnutrition typically affects the junior/youngest siblings, which additionally suffer from higher ectoparasite burden (‘tasty chick hypothesis’; Roulin et al 2003 ; Sumasgutner et al, 2014c ).…”

Settlement Phenotypes: Social Selection and Immigration in a Common Kestrel Population

“…Furthermore, in females it was positively correlated with productivity, measured as the number of fledged chicks. In our population, kestrels prey on a variety of prey species, but they have a markedly predilection for voles (Fargallo et al, 2020) and individuals hunting more voles have lower wing-to-tail ratios (Fargallo unpublished data). These results indicate that tail length reflects individual quality in both males and females either by indicating hunting abilities and nutritional state.…”

Two wild carnivores selectively forage for prey but not amino acids

“…Determining whether wild carnivores can accomplish these patterns of intake in complex natural habitats is far more difficult. A recent study provided evidence that common kestrels ( Falco tinnunculus ) select prey in the wild with high contents of sulfur amino acids 41 , but as has been the case for studies of macronutrient selection by carnivores, this study did not characterise the intake target. If we are to determine the extent to which the well-developed theoretical framework of nutritional ecology applies to carnivores, then tests of its hypotheses and assumptions are required using wild carnivore populations whose nutrient intake targets are defined.…”