Academic journal article The American Midland Naturalist

Comparative Spring-Staging Ecology of Sympatric Arctic-Nesting Geese in South-Central Nebraska

Academic journal article The American Midland Naturalist

Comparative Spring-Staging Ecology of Sympatric Arctic-Nesting Geese in South-Central Nebraska

Article excerpt

ABSTRACT.-

The Rainwater Basin in Nebraska has been a historic staging area for midcontinent greater white-fronted geese (Anser albifrons fiontalis) since the 1950s and, in the mid-1990s, millions of midcontinent lesser snow geese (Chen caerulescens caerulescens) expanded their spring migration route to include this region. In response to speculation that snow geese may be in direct competition with white-fronted geese, we compared staging ecology by quantifying diet, habitat use, movement patterns, and time budgets during springs 1998-1999. Collected white-fronted geese (n = 190) and snow geese (n = 203) consumed primarily corn (Zea mays; 97-98% aggregate dry mass) while staging in Nebraska; thus, diet overlap was nearly complete. Both species used cornfields most frequently during the morning (54-55%) and wetlands more during the afternoon (51-65%). When found grouped together, snow goose abundance was greater than white-fronted goose abundance by an average of 57 times (SE = 11, n = 131 groups) in crop fields and 28 times (SE = 9, n = 84 groups) in wetlands. Snow geese and white-fronted geese flew similar distances between roosting and feeding sites, leaving and returning to wetland roost sties at similar times in mornings and afternoons. Overlap in habitat-specific time budgets was high; resting was the most common behavior on wetlands, and foraging was a common behavior in fields. We observed 111 interspecific agonistic interactions while observing white-fronted and snow geese. White-fronted geese initiated and dominated more interactions with other waterfowl species than did snow geese (32 vs. 14%). Certain aspects of spring-staging niches (i.e., diet, habitat use, movement patterns, and habitat-specific behavior) of white-fronted and snow geese overlapped greatly at this mid-latitude staging site, creating opportunity for potential food- and habitat-based competition between species. Snow geese did not consistently dominate interactions with white-fronted geese; yet large differences in their numbers coupled with high degrees of spatial, temporal, and ecological overlap support potential for exploitative competition during years when waste corn may be in short supply and dry years when few wetlands are available for staging waterfowl.

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INTRODUCTION

'Migrating birds must continually search for safe and suitable staging habitats containing abundant resources while traveling between wintering and breeding grounds. Replenishing energy expended during long distance flight and nutrient storage necessary for breeding represent extensive energetic challenges migratory birds must overcome (Ankney and Maclnnes, 1978). Migration also can be a time when species that use distinct winter or breeding areas congregate at stopover areas within a common migration corridor. Species exploiting similar and limited resources during migration may experience intensified interspecific interactions because of increased energetic requirements and high densities of potential competitors (Moore and Yong, 1991).

Understanding niche overlap during various portions of the annual cycle of avian species, including migration, provides insight into their distributions and coexistence (DuBowy, 1988; Wiens, 1989). Isolation or partitioning of common and limited resources may reduce competitive pressures among sympatric species (MacArthur, 1958). Resource partitioning facilitates coexistence when species reflect a high degree of overlap (Schoener, 1974). Potential partitioning mechanisms include dietary, spatial, temporal, and behavioral variation. For species that exist in sympatry during only a portion of their annual cycle, such as migration, resource partitioning may be less pronounced because of reduced time to adequately develop such relationships.

Numerous waterbirds migrating across the Great Plains of North America converge on south-central Nebraska, using wetlands in the Rainwater Basin and along the central Platte River (U. …

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