Interspecific and intraspecific differences in habitat use and their conservation implications for Palaearctic harriers on Sahelian wintering grounds

Abstract

The floodplains of the West‐African Sahel region have experienced extensive habitat transformation during the past four decades, coinciding with an impoverishment of raptor populations. We investigated foraging patterns of Palaearctic migratory Eurasian Marsh Harriers Circus aeruginosus, Pallid Harriers C. macrourus and Montagu’s Harriers C. pygargus on a floodplain system in northern Cameroon to assess species, sex‐ and age‐related habitat preferences. Sex and age have rarely been incorporated into general studies of raptor habitat associations, despite clear evidence of intrasexual and age‐related differences in foraging strategies and diet composition, potentially carrying strong conservation implications. We found evidence of sexual differences in foraging preference related to land use, particularly in the most sexually dimorphic Pallid Harrier, and evidence that juveniles used different habitats to adults. This constitutes the first quantitative documentation of such differentiation by Palaearctic raptors on African wintering grounds, indicating that general patterns of habitat use in wintering raptors may obscure sex‐ and age‐specific preferences. Contrary to expectations, we found limited evidence for interspecific foraging segregation. Food partitioning by prey mass was related to harrier body mass and facilitated by a diverse availability of prey on human‐transformed floodplains. Anticipated further large‐scale conversion of floodplain habitat into predominantly desiccated grasslands raises concerns about the survival of wintering harriers.

Determining conservation priority areas for Palearctic passerine migrant birds in sub-Saharan Africa

“…Although many studies have suggested possible conservation measures for the breeding grounds (e.g., Arroyo et al 2002, Donald et al 2007, Fuller et al 2007, Newton 2008, fewer have done so for the wintering grounds (e.g., Zwarts et al 2009, Walther et al 2010, 2011, Buij et al 2012, Limiñana et al 2012, Walther 2016.…”

Using satellite telemetry and environmental niche modelling to inform conservation targets for a long-distance migratory raptor in its wintering grounds

“…This may be related to differences in winter diets. The pallid harrier is a small-rodent specialist during breeding (Terraube et al, 2011) and small mammals and passerines contribute a large proportion of its total biomass consumption in winter (Buij et al, 2012). Hence, if pallid harriers reach an area of high vertebrate prey abundance in winter they may settle and remain there.…”

“…Ideally, model predictions should be validated by field observations. Further research is also needed to identify the most profitable foraging habitats for pallid harriers at local scales, as done by Buij et al (2012). Detailed field studies on diet, prey (passerine birds, grasshoppers and small rodents) abundance and foraging success in different habitats (e.g.…”

“…Individual variations in migration and wintering behaviour probably depend on resource distribution, as well as experience and condition (e.g. energy stores, breeding status, predation risk, prior knowledge), and even sex (Buij et al, 2012).…”

“…The migratory routes and wintering range of pallid harriers breeding in Kazakhstan and adjacent areas of Russia have been described using satellite telemetry (Terraube et al, 2012). Buij et al (2012) showed that pallid harriers wintering in northern Cameroon preferentially used rice fields and flooded grasslands, with evidence of sexual differences in habitat use when foraging. However, general knowledge about the ranging behaviour and habitat use of this species during the non-breeding period is lacking and this impedes conservation.…”