Wildlife Conservation Sunflower Plots and Croplands as Fall Habitat for Migratory Birds

Article excerpt

ABSTRACT.

Agricultural fields are often overlooked as post-breeding and migratory bird habitat, even though many species use row-crop fields in the northern Great Plains. We monitored bird use, crop and non-crop vegetation characteristics and abundance, and land use around (≤2.4 km) 35 8-ha Wildlife Conservation Sunflower Plots (WCSP) and one commercial sunflower and non-sunflower row-crop field, paired with each WCSP, in fall 2004 and 2005. We excluded four species of blackbirds from our analysis that commonly form large foraging flocks and ubiquitously use agricultural fields. A diverse community of migratory birds used WCSP and commercial sunflower compared to other non-sunflower crops in North Dakota. Both WCSP (mean = 24.4 birds/ha, SE = 2.7) and commercial sunflower (mean = 12.7 birds/ha, SE = 1.7) harbored greater densities of birds (P < 0.01) than did other non-sunflower row crops (mean = 7.2 birds/ha, SE = 1.1). Migratory birds were more strongly associated with vegetation within fields, such as crop density (+), non-crop plant abundance (+) and crop height (+), than surrounding land uses (0-2.4 km from WCSP). We recommend management practices to maximize WCSP for fall bird habitat and discuss economic considerations for WCSP implementation as a wildlife habitat / blackbird damage management system.

INTRODUCTION

Agricultural crops provide habitat for migratory birds in the northern Great Plains (NGP) of North America during and before migration periods. Extensive cultivation of crops has fragmented >50% of prairies in the NGP and likely influenced bird communities in the region (Peterjohn, 2003; Lubowski et al, 2006). Few studies have examined migratory bird use of croplands in North America, especially during non-breeding periods, even though croplands represent the third-largest land use (19.5%) in the United States (Lubowski et al, 2006).

Birds migrating during fall likely select staging habitat hierarchically based on foraging and energy demands of migration, landscape composition and weather (Johnson, 1980; Kolasa, 1989; Kotliar and Wiens, 1990; Bergin, 1992; Moore and Simons, 1992; Moore and Aborn, 2000) . Croplands may be selected based on patch quality detectable from proximate cues or composition of habitat complexes (Best et al, 1990, 1998; Flather and Sauer, 1996; Koford and Best, 1996; Schaaf, 2003; Galle, 2005; Pearse, 2007). Within selected landscapes, land use diversity surrounding roost and loafing sites and vegetative characteristics within fields likely influence field selection and subsequent use (Stone and Danner, 1980; Best et al, 2001; Cunningham and Johnson, 2006). Some croplands within the NGP may provide disproportionately important habitat given crop characteristics, farming practices, time of harvest relative to other crops and associated food resources.

Birds use sunflower and other crops during migration through the NGP (Best et al, 1998; Murphy, 2003; Hagy et al, 2007), but we know little about landscape-scale or within-field variables influencing use (Moore et al, 1995; Peterjohn, 2003) . Sunflower is used extensively by migrating birds, especially after mid- to late-summer harvest and tilling of other row crops reduce vegetation and vertical structure of croplands in the NGP (Schaaf, 2003; Linz et al, 2003). In late summer and fall, an energy-rich and structurally diverse crop (Schaff, 2003) such as sunflower may be easily recognizable as a source of cover and food for a variety of birds (Charlet et al, 1997; Linz et al, 2004; Hagy et al, 2007).

Blackbirds [red-winged blackbirds (Agelaius phoeniceus), Brewer's blackbird (Euphagus cyanocephalus) , common grackles (Quiscalus quiscula) and yellow-headed blackbirds (Xanthocephalus xanthocephalus)] extensively use sunflower fields and subsequently cause economically important damage by feeding on ripening sunflower seeds (Otis and Kilburn, 1988; Peer et al, 2003; Hagy et al, 2008). Traditional harassment and damage prevention methods are time-intensive, expensive and negatively affect other wildlife and bird species (Kleingärtner, 2003; Linz et al, 2003). …