Snake activity affects seasonal variation in nest predation risk for birds

Abstract

Variation in predator behavior has been proposed, but not tested, as a mechanism producing seasonal declines in avian nest success. We test this hypothesis by documenting seasonal activity of Texas ratsnakes Elaphe obsoleta and nest failure of endangered black-capped vireos Vireo atricapilla and golden-cheeked warblers Dendroica chrysoparia on which the snakes prey. Nest survival analysis was based on 880 vireo and 228 warbler nests and 3,060 snake locations from 62 radio-tracked snakes. Although nest success varied with snake activity for both birds, specific patterns differed substantially. Vireo daily nest survival was negatively correlated with snake activity over the three-year study, despite substantial variation among years in weather, and the fact that these birds are almost certainly a minor prey species of the ratsnakes. Warblers exhibited less clear-cut seasonal variation in nest success, and the association between nest success and snake activity was less pronounced than for vireos. Increased activity at warmer temperatures explained some of the seasonal change in snake movements, although mating may have accounted for a mid-season peak in activity. These results indicate that variation in predator behavior can be associated with and potentially cause seasonal changes in nest success, but also that these relationships are species specific even within the same community and may depend on aspects of the nesting ecology of the prey such as nest site selection.

Variables associated with nest survival of Golden-winged Warblers (Vermivora chrysoptera) among vegetation communities commonly used for nesting

“…Predation is the presumed cause of nearly all Golden-winged Warbler nest failures, particularly by small mammals and snakes (Kubel and Yahner 2008, Confer et al 2010, Bulluck et al 2013, Streby et al 2014, similar to other ground-nesting birds (Söderström et al 1998, Thompson and Burhans 2003, Weatherhead and Blouin-Demers 2004, Sperry et al 2008. Nest predation patterns can be best explained with a hierarchical, multiscale modeling approach, where landscape-scale characteristics are most important and provide context for predation patterns at the nest-site scale (Thompson et al 2002).…”

“…Passerine nest survival tends to decrease over time within a season (Grant et al 2005, Bulluck et al 2013, but in some cases may increase (Streby et al 2014). Within-season trends in DSR may be curvilinear because of changing activity patterns of nest predators such as snakes, whose activity varies with reproductive and thermoregulatory stimuli (Sperry et al 2008). Thus, we tested if DSR had a linear or quadratic relationship with time-within-season.…”

Crumbling diversity: comparison of historical archived and contemporary natural populations indicate reduced genetic diversity and increasing genetic differentiation in the golden-cheeked warbler

“…We did not estimate N e / N c ratios in D. chrysoparia as there is little information about historical census sizes, making such a comparison impossible. The relatively small estimates of N e observed in our study may be a consequence of various demographic factors related to habitat loss and fragmentation, and may reflect poor survival in habitat edges (Lindsay et al 2008), reduced nest success in degraded habitats (Peak 2007;Reidy et al 2009), high levels of brood parasitism and nest predation (Sperry et al 2008), or limitation of habitat on wintering grounds (Rappole et al 2003). A follow-up temporal analysis of the managed populations will be required to assess if and how N e is changing in response to management efforts.…”

“…Fragmentation of available habitat is known to have resulted from clearing of woodlands for livestock production and agriculture. Populations are also depressed due to brood parasitism by brown-headed cowbirds, Molothrus ater (Sperry et al 2008).…”

Indirect effect of climate change: Shifts in ratsnake behavior alter intensity and timing of avian nest predation

“…This work predicts both an expansion of seasonal snake activity in response to warmer climates, with snakes becoming active earlier in the spring and continuing later in the fall, and a shift in diel patterns, with snakes in warmer climates switching from diurnal to nocturnal activity at the warmest time of the year. Because snake activity and behavior can be directly linked to songbird nest predation risk (Sperry et al, 2008;Klug et al, 2010;Weatherhead et al, 2010;Cox et al, 2013;DeGregorio et al, 2014b), this shift in seasonal and nocturnal activity is likely to alter the predator-prey interactions between snakes and birds, most likely to the detriment of bird populations.…”