Grassland Songbird Survival and Recruitment in Agricultural Landscapes: Implications for Source–sink Demography

Abstract

Population growth and decline are particularly sensitive to changes in three key life-history parameters: annual productivity, juvenile survival, and adult survival. However, for many species these parameters remain unknown. For example, although grassland songbirds are imperiled throughout North America, for this guild, only a small number of studies have assessed these parameters. From 2002 to 2006, in the agricultural landscape of the Champlain Valley of Vermont and New York, USA, we studied Savannah Sparrow (Passerculus sandwichensis) and Bobolink (Dolichonyx oryzivorus) demography on four grassland treatments: (1) early-hayed fields cut before 11 June and again in early- to mid-July; (2) middle-hayed fields cut once between 21 June and 10 July; (3) late-hayed fields cut after 1 August; and (4) rotationally grazed pastures. We assessed whether these treatments affected adult apparent survival (phi) and recruitment (f), how sensitive these parameters were to the presence of nonbreeders and local dispersal, and the populations' ability to persist in these four habitats. On average, birds using late-hayed fields had > 25% higher apparent survival than those on the more intensively managed early-hayed, middle-hayed, and grazed fields. Overall male phi was 35% higher than female phi, and Savannah Sparrow phi was 44% higher than Bobolink phi. Across all analyses and treatments, apparent survival estimates were 0.58-0.85 for male and 0.48-0.71 for female Savannah Sparrows, and 0.52-0.70 for male and 0.19-0.55 for female Bobolinks. For males of both species, potential nonbreeders decreased the precision of and lowered apparent survival estimates by 25%; female estimates showed little variation with the inclusion of nonbreeders. Inclusion of local dispersal observations increased apparent survival estimates and, in many cases, increased precision, though the effect was stronger for Savannah Sparrows than for Bobolinks, and also stronger for males than for females. High Savannah Sparrow apparent survival rates resulted in stable or near stable populations (lambda approximately 1), particularly in late-hayed and grazed fields, while low Bobolink apparent survival rates resulted in strongly declining populations (lambda < 1) in all treatments.

Breeding Biology of Grassland Birds in Western New York: Conservation and Management Implications

“…A second objective was to compare our data on nesting success of obligate grassland breeding birds from a site near the periphery of their range, i.e., in the Northeast, to published data from the Midwest, considered to be the center of distribution in North America for most grassland species and their habitats (Vickery et al 1999). Data from our study supplement those from other studies of obligate grassland bird breeding biology in the Northeast (Bollinger and Gavin 1992, Vickery et al 1992a, Wells 1997, Balent and Norment 2003, Perlut et al 2006, Perlut et al 2008; together, these provide a context for evaluating efforts to conserve obligate grassland breeding birds in the region.…”

“…In terms of disturbance, none of our study sites were mowed, hayed, or grazed until after 1 August, by which time grassland breeding birds had fledged young (Table 1). In contrast, early haying had strong negative effects on grassland bird productivity (Perlut et al 2006) and survival (Perlut et al 2008) in Vermont; nest success of Bobolinks in New York (Bollinger et al 1990); and Eastern Meadowlarks in Illinois (Roseberry and Klimstra 1970).…”

Grassland Bird Productivity in Warm Season Grass Fields in Southwest Wisconsin

“…On average, adults using late-hayed fields have a 25% higher survival rate than those using early-hayed and grazed fields (Perlut et al, 2008). Daily survival rate is apparently lower during incubation than during rearing stages (Scheiman et al, 2007).…”

“…The apparent survival rate of adults in New England ranges from 0.52-0.70 for males and 0.19-0.55 for females; these rates are considered relatively low (Perlut et al, 2008). On average, adults using late-hayed fields have a 25% higher survival rate than those using early-hayed and grazed fields (Perlut et al, 2008).…”

Nestling diet optimization and condition in relation to prey attributes and breeding patch size in a patch-resident insectivorous passerine: an optimal continuum and habitat constraints

“…The primary breeding habitat of Whinchat used to be invertebrate-rich grasslands, especially those lying within traditionally managed agricultural landscapes, where the abundance and diversity of arthropod prey were higher than in intensively managed grasslands (Oppermann 1999;Bastian and Bastian 1996;Britschgi et al 2006;Broyer et al 2012;Strebel et al 2015). The recent population decline of grassland birds, including the Whinchat, has been ascribed mainly to nest losses/female mortality resulting from more intensive agriculture practices, primarily earlier and more frequent mowing (Grüebler et al 2008(Grüebler et al , 2012, deteriorating food/foraging conditions in semi-natural grasslands/meadows and the loss of marginal habitats (Müller et al 2005;Britschgi et al 2006;Perlut et al 2008;Broyer 2009;Broyer et al 2012Broyer et al , 2014Henderson et al 2014;Strebel et al 2015). A very recent investigation has found evidence that mortality in Whinchats occurs primarily outside the wintering period, i.e.…”