Predator movements in relation to habitat features reveal vulnerability of duck nests to predation

Abstract

Nest predation is the main cause of nest failure for ducks. Understanding how habitat features influence predator movements may facilitate management of upland and wetland breeding habitats that reduces predator encounter rates with duck nests and increases nest survival rates. For 1618 duck nests, nest survival increased with distance to phragmites (Phragmites australis), shrubs, telephone poles, human structures, and canals, but not for four other habitat features. Using GPS collars, we tracked 25 raccoons (Procyon lotor) and 16 striped skunks (Mephitis mephitis) over 4 years during waterfowl breeding and found marked differences in how these predators were located relative to specific habitat features; moreover, the probability of duck nests being encountered by predators differed by species. Specifically, proximity to canals, wetlands, trees, levees/roads, human structures, shrubs, and telephone poles increased the likelihood of a nest being encountered by collared raccoons. For collared skunks, nests were more likely to be encountered if they were closer to canals, trees, and shrubs, and farther from wetlands and human structures. Most predator encounters with duck nests were attributable to a few individuals; 29.2% of raccoons and 38.5% of skunks were responsible for 95.6% of total nest encounters. During the central span of duck nesting (April 17–June 14: 58 nights), these seven raccoons and five skunks encountered >1 nest on 50.8 ± 29.2% (mean ± SD) and 41.5 ± 28.3% of nights, respectively, and of those nights individual raccoons and skunks averaged 2.60 ± 1.28 and 2.50 ± 1.09 nest encounters/night, respectively. For collared predators that encountered >1 nest, a higher proportion of nests encountered by skunks had evidence of predation (51.9 ± 26.6%) compared to nests encountered by raccoons (22.3 ± 17.1%). Because duck eggs were most likely consumed as raccoons and skunks opportunistically discovered nests, managing the habitat features those predators most strongly associated with could potentially reduce rates of egg predation.

Northern bobwhite breeding season and nest survival are greater on native grasslands

“…Mammals and snakes are responsible for 40.2%, and 31.7% of nests depredated, respectively, and raccoons are the most common mammalian predator of bobwhites in Georgia, USA (Terhune et al 2008). Raccoons select trees and agriculture while avoiding open grasslands (McClain 2017, Peterson et al 2022). They also use tree lines, fencerows, timber‐grassland edges, and woody draws as movement corridors (Pedlar et al 1997, Barding and Nelson 2008, McClain 2017, Peterson et al 2022).…”

“…Raccoons select trees and agriculture while avoiding open grasslands (McClain 2017, Peterson et al 2022). They also use tree lines, fencerows, timber‐grassland edges, and woody draws as movement corridors (Pedlar et al 1997, Barding and Nelson 2008, McClain 2017, Peterson et al 2022). Mesocarnivores likely remain near woody cover and avoid open grassland to avoid predation by coyotes or bobcats ( Lynx rufus ; Tewes et al 2002, Kamler and Gipson 2003).…”

“…We quantified local cover type composition as percent cover within a 100‐m radius of each bird and nest location. While bobwhites likely respond to vegetation composition and structure at micro and macro scales (Taylor et al 1999 a , Yeiser et al 2021, Sinnott et al 2023 b ), we restricted our scale of interest to a radius in which vegetation composition and structure could vary daily with movements of individual bobwhites and that captured proximity of vegetation features associated with predator risk (Peterson et al 2022, Sinnott et al 2022). We selected a scale of interest based on prior knowledge of bobwhite and predator movements and vegetation associations, but we did not identify the optimal scale to evaluate demographic–environmental relationships (Monroe et al 2022).…”

“…Predation is a substantial source of mortality for bobwhite chicks in summer and juveniles and adults in fall and winter in Missouri (Mosloff 2020, Sinnott et al 2022). Land cover composition and land management practices influence the suitability of landscapes for predators, and consequently predation risk and demographic rates of bobwhite occupying those landscapes (Rectenwald et al 2021, Peterson et al 2022). Trees can harbor predators such as Virginia opossums ( Didelphis virginiana ), raccoons ( Procyon lotor ), and raptors (Dijak and Thompson 2000, Byrne and Chamberlain 2011).…”

“…Racoons are more abundant in agricultural landscapes, especially along forest edges adjacent to agricultural fields (Pedlar et al 1997, Dijak and Thompson 2000). Nest proximity to features such as trees, roads, or human structures can increase the likelihood of encounters with raccoons or striped skunks ( Mephitis mephitis ; Peterson et al 2022). Shrubs can provide escape cover for bobwhites from predators (Brennan 1991, Williams et al 2000, Sandercock et al 2008, DeMaso et al 2014).…”