Multi-scale landscape effects on incubation behaviours in boreal nesting ducks

Abstract

Incubation plays a crucial role in embryonic development and influences nest and adult survival in birds. Among most North American duck species, only females incubate eggs and therefore face a trade-off between self-maintenance and incubation. These patterns of attendance represent incubation behaviour and are influenced by various external factors that can affect the overall fitness of females and their offspring, but we lack an understanding of how habitat structure and composition affects incubation behaviour. We measured incubation recess frequency, duration and incubation constancy in four ground-nesting duck species (at five nests of Mallard Anas platyrhynchos, 12 Blue-winged Teal Spatula discors, five Green-winged Teal Anas crecca, and seven American Wigeon Mareca americana) across a gradient of natural resource development in the western boreal forest of Alberta, Canada. To quantify incubation patterns, we developed a behaviour identification method using a combination of observer-mediated changepoint analyses and generalized additive models. We then examined the effects of important land cover (e.g. marsh), land use (e.g. roads) and temperature on incubation behaviour using generalized linear mixed-effect models. Average (± s.e.) daily recess frequency for all species was 2.81 ± 0.251 breaks per day, with an average break duration of 3 h (183.49 ± 29.52 min). Across species, individuals spent on average 67% (0.67 ± 0.038) of their day incubating. Daily recess frequency was positively correlated with secondary roads (e.g. winter roads, trails, unmaintained roads), overhead cover at the nest site, marsh habitat and air temperature. Recess duration was positively correlated with average air temperature; incubation constancy was negatively correlated with average air temperature and overhead cover. The results suggested that incubating females take more recesses per day in response to increased land cover, land use and temperature; and that they adjust the duration of recesses and incubation constancy in response to warmer weather. This research yields baseline information on the incubation behaviour of boreal ducks, and uses a new quantitative approach to describe the effects of habitat structure and composition on the incubation behaviour of ground-nesting ducks in the western boreal forest.