Location and agricultural practices influence spring use of harvested cornfields by cranes and geese in Nebraska

Abstract

Millions of ducks, geese, and sandhill cranes (Grus canadensis; hereafter cranes) stop in the Central Platte River Valley (CPRV) of Nebraska to store nutrients for migration and reproduction by consuming corn remaining in fields after harvest. We examined factors that influence use of cornfields by cranes and geese (all mid‐continent species combined; e.g., Anser, Chen, and Branta spp.) because it is a key step to efficient conservation planning aimed at ensuring that adequate food resources are available to migratory birds stopping in the CPRV. Distance to night‐time roost site, segment of the CPRV (west to east), and agricultural practices (post‐harvest treatment of cornfields: idle, grazed, mulched, mulched and grazed, and tilled) were the most important and influential variables in our models for geese and cranes. Probability of cornfield use by geese and cranes decreased with increasing distance from the closest potential roosting site. The use of cornfields by geese increased with the density of corn present there during the early migration period, but field use by cranes appeared not to be influenced by early migration corn density. However, probability of cornfield use by cranes did increase with the amount of wet grassland habitat within 4.8 km of the field. Geese were most likely to use fields that were tilled and least likely to use fields that were mulched and grazed. Cranes were most likely to use fields that were mulched and least likely to use fields that were tilled, but grazing appeared not to influence the likelihood of field use by cranes. Geese were more likely to use cornfields in western segments of the CPRV, but cranes were more likely to use cornfields in eastern segments. Our data suggest that managers could favor crane use of fields and reduce direct competition with geese by reducing fall and spring tilling and increasing mulching. Moreover, crane conservation efforts would be most beneficial if they were focused in the eastern portions of the CPRV and in fields as close as possible to both known roosting and large amounts of wet grassland habitats. © 2011 The Wildlife Society.

Agricultural practices and residual corn during spring crane and waterfowl migration in Nebraska

“…Baldassarre et al (1983) proposed that burning stubble may make corn more available to birds because it removes litter that covers residual corn, although this was not a commonly used management practice in the CPRV during our study. Despite lower corn abundance, Anteau et al (2011) noted that sandhill cranes in the CPRV used mulched cornfields more than any other treatment, potentially because cranes favored fields with less standing stubble or because mulched fields may have higher densities of other food items (e.g., invertebrates). Thus, field use by cranes may be influenced by trade‐offs among desirable structure (e.g., low cover), abundance of residual corn, and efficiency of foraging through litter.…”

“…Tilled fields had the lowest corn density of any treatment, likely because corn cobs and kernels were broken up and buried during tillage. Despite low corn abundance, Anteau et al (2011) noted that geese in the CPRV used tilled fields more than other treatments. Jorde et al (1983) suggested that foraging efficiency of mallards ( Anas platyrhynchos ) was higher in tilled fields because of a decrease in litter at the surface.…”

“…We suspect that these outcomes resulted from differences among post‐harvest treatments in foraging efficiency and field selection probability by migratory birds. A companion study in the CPRV (Anteau et al 2011) showed that tilled fields had the highest probability of use by geese and the lowest probability of use by cranes, suggesting that foraging by geese may be a primary factor influencing corn depletion in these fields. Little is known about the relative foraging efficiency of geese and cranes, or how foraging efficiency varies among management treatments.…”

“…Because stubble structure varies substantially, ranging from bare dirt in tilled fields to standing stubble in idle fields, it is also likely that residual corn is not equally available to foraging birds among treatments, even if density were comparable. Thus, depletion of corn is probably driven by a complex interaction of residual corn abundance, post‐harvest treatment, foraging efficiency, and proximity to suitable goose and crane roost sites (Anteau et al 2011). Greer et al (2009) also found that density of waste rice remaining in fields after waterfowl stopped feeding (i.e., giving‐up density) did not differ among post‐harvest management treatments, suggesting that food density was the primary factor driving foraging decisions in that system.…”

Bird use of grain fields and implications for habitat management at airports

“…Snow geese (Chen caerulescens) select waste corn over wheat and soybeans (Frederick and Klaas, 1982). Canada goose (Branta canadensis) and other waterfowl have demonstrated differential field use based on waste corn density (Anteau et al, 2011). As cover, fields with standing stubble of cereal crops and oilseed were used by more granivores than fields with traditional tillage in Europe and North America (Castrale, 1985;Donald and Forrest, 1995;Chamberlain et al, 1999;Gillings et al, 2005;Kopij, 2008;Kragten and de Snoo, 2008).…”