Agricultural habitat use and selection by a sedentary bird over its annual life cycle in a crop-depredation context

Abstract

Background: Modern agriculture has undoubtedly led to increasing wildlife-human conflicts, notably concerning bird damage in productive and attractive crops during some parts of the annual cycle. This issue requires utmost attention for sedentary birds that may impact agricultural crops at any stage of their annual life cycle. Reducing bird-human conflicts requires a better understanding of the relationship between bird foraging activity and the characteristics of agricultural areas, notably with respect to changes in food-resource availability and crop sensitivity across the year.

Methods: We explored how GPS-tagged adult male western jackdaws- sedentary corvids- utilize agricultural areas throughout their annual cycle, in a context of crop depredation. More precisely, we described their daily occurrence distribution and the extent of habitat use and selection consistency with respect to landscape composition across time.

Results: Jackdaws moved in the close agricultural surroundings of their urban nesting place over the year (< 2.5 km from the nest, on average). Daily occurrence distributions were restricted (< 2.2 km²), relatively centered on the nesting locality (distance between the daily occurrence centroid and the nest < 0.9 km), and rather spatially stable during each annual life-cycle period (overlap range: 63.4-76.1%). Their foraging patterns highlighted that they fed mainly in grasslands all year round, and foraged complementarily and opportunistically in maize (during sowing- coinciding with the first stages of the birds' breeding period) and cereal crops (during harvesting- their post-fledging period).

Conclusions: Our findings demonstrate the very limited space use by breeding male jackdaws which foraged preferentially in grasslands. We call for future investigations in other agricultural contexts and also considering non-breeders for extrapolation purposes.

Keywords: Corvus monedula; Crop damage; Foraging duration; GPS telemetry; Land use; Occurrence distribution; Resource selection.

Fig. 1

Peak periods of sowing and harvesting matching with tracking periods (gray rectangles) throughout the annual life cycle of jackdaws (thick gray lines as biological periods). We focused on maize and cereal (wheat and barley, mostly) which are the main depredated crops in our study area [40]. Red and green, peak periods of sowing and harvesting, respectively

Fig. 2

Variation in daily occurrence distribution according to the biological periods of jackdaws. The four descriptors used are (A) daily occurrence area (km²), (B) extent of the (intra-period) spatial overlap of the daily occurrence distributions (%), (C) distance between the daily occurrence centroid and the nest location (km), and (D) distance between the farthest limit of the daily occurrence distribution and the nest location (km). Mean estimates and 95% confidence intervals are provided. Different letters indicate statistically different values (increasing values arranged in alphabetical order)

Fig. 3

Variation in daily foraging duration spent by jackdaws in different habitats according to their biological periods. Habitats are (A) grasslands, (B) cereal crops, and (C) maize crops. Mean estimates (min) and 95% confidence intervals are provided. Different letters indicate statistically different values (increasing values arranged in alphabetical order)

Fig. 4

Relative selection strength estimates for foraging habitats by jackdaws throughout their annual life cycle. Biological periods are (A) nest building, (B) incubation, (C) chick rearing, (D) post fledging, (E) post breeding, and (F) wintering. Estimates (mean values with 95% confidence intervals; exponentiated coefficients) were compared to the selection strength computed for grasslands as a reference level (dashed line; all comparisons led to p < 0.001, except for maize during incubation). Values above and below the dashed line indicate higher and lower relative intensities of use, respectively, under equal habitat availability with grasslands