Factors influencing diet variation in a generalist predator across its range distribution

Abstract

ABSTRACT:1 Factors linked with intraspecific variation in trophic diversity are still poorly understood in 2 generalist species like the Montagu's harrier (Circus pygargus). We described geographic 3 patterns of Montagu's harrier diet across Eurasia, gathering diet data from 30 studies in 41 areas 4 from 11 countries. We grouped prey as invertebrates, reptiles, small mammals, large mammals, 5 eggs, small birds and large birds, and calculated the contribution of each prey type to the diet (as 6 % biomass) and Shannon's Diversity Index for each study site. We analysed the diversity index 7 and qualitative estimates of prey abundance in relation to latitude and longitude, then diet 8 composition in relation to habitat of the study area and prey abundance estimates. Diet diversity 9 of Montagu's harriers increased from north to south, while abundance of all prey groups other 10 than small mammals showed the opposite trends. Agricultural areas in northern latitudes seemed 11 to hold high densities of small mammals, but low densities of alternative prey. Overall, birds 12 were the main prey in most of Montagu's harrier's distribution range, although the relative 13 importance of each prey type in the diet was significantly explained by its local abundance and 14 habitat, confirming the opportunistic foraging strategy of this raptor species. Consumption of 15 mammals was an exception to this trend, being negatively associated with the abundance of 16 alternative prey, suggesting that this prey is not preferred. Trophic diversity in this species could 17 be influenced by land-use changes through variations in the abundance and availability of prey,

Functional biogeography of dietary strategies in birds

“…Regression lines correspond to the 0.1, 0.25, 0.5, 0.75 and 0.90 quantiles, and grey dots depict partial residuals [Colour figure can be viewed at wileyonlinelibrary.com] space, a necessary perspective to enforce its macroevolutionary underpinnings (Violle et al, 2014). Furthermore, in addition to spatial variations across populations (Terraube & Arroyo, 2011), species may use different diets depending on age, sex, environmental constraints or resource availability (Davies, Hipfner, Hobson, & Ydenberg, 2009;León, Podos, Gardezi, Herrel, & Hendry, 2014;Murphy, 1994). In particular, numerous migratory species typically shift from insectdominated diets to fruits at the onset of migration, whereas the diets of sedentary species follow food availability across seasons (Lovette & Fitzpatrick, 2016;Newton, 2010).…”

Feeding behaviour and diet composition of Marsh Harriers Circus aeruginosus in agricultural landscapes

“…Under this perspective it seems that the diet of Marsh Harriers in intensively managed farmland (with a higher proportion of small mammals and less diverse than in traditional farmlands) could be the result of the particularly favourable foraging conditions offered by this habitat in terms of optimal prey availability, as has been suggested by previous studies on ranging behaviour and habitat use , Cardador & Mañ osa 2011. However, this is not the only possible interpretation, as a high percentage of small mammals in the diet of Marsh Harriers in intensively managed habitats could also be a by-product of there being relatively few alternative prey, such as birds (Terraube & Arroyo 2011). More specific studies on foraging efficiency and time budgets in different habitats with prey types are needed to clarify whether small mammals or birds have higher or equal value for Marsh Harriers (Terraube et al 2010) and whether the higher consumption of small mammals in intensively managed farmland is the outcome of an optimal foraging strategy or the result of a reduction of alternative prey diversity and availability.…”

Irruptive movements and breeding dispersal of snowy owls: a specialized predator exploiting a pulsed resource

“…Consumers have developed several strategies to cope with variable or pulsed food sources. Indeed, in the presence of highly variable resources, some species broaden their diet in order to maximize energy gain (Terraube and Arroyo ) while others rely on hoarded resources (Careau et al ) or reduce metabolic (or reproductive) activities until the next resource pulse (Stearns ).…”