What seeds tell us about birds: a multi-year analysis of acorn woodpecker foraging movements

Movement Ecology

Victoria L Sork¹  Douglas G Scofield³  Peter E Smouse²  Pamela G Thompson⁴ 

[1] Institute of the Environment and Sustainability, University of California Los Angeles, Los Angeles, CA 90095-1496, USA;Department of Ecology, Evolution and Natural Resources, Cook College, Rutgers University New Brunswick, Brunswick, NJ 08901-8551, USA;Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, SE-75236, Uppsala, Sweden;Department of Ecology and Evolutionary Biology, University of California Los Angeles, Los Angeles, CA 90095-7239, USA

关键词: Beta and Gamma diversity;    Alpha;    territoriality;    Foraging movement;    Acorn woodpeckers;    Seed movement;    Optimal foraging theory;   

Others  :  810305
DOI  :  10.1186/2051-3933-2-12

 received in 2014-02-03, accepted in 2014-06-04,  发布年份 2014

【 摘 要 】

Background

Foraging movements of animals shape their efficiency in finding food and their exposure to the environment while doing so. Our goal was to test the optimal foraging theory prediction that territorial acorn woodpeckers (Melanerpes formicivorus) should forage closer to their ‘central place’ in years of high resource availability and further afield when resources are less available. We used genetic data on acorns stored in caching sites (granaries) and adult trees for two oak species (Quercus lobata and Quercus agrifolia) to track acorn movements across oak savanna habitat in central California. We also compared the patterns of trees these territorial bird groups foraged upon, examining the effective numbers of source trees represented within single granaries (α), the effective number of granaries (β), the diversity across all granaries (γ), and the overlap (ω) in source trees among different granaries, both within and across years.

Results

In line with optimal foraging theory predictions, most bird groups foraged shorter distances in years with higher acorn abundance, although we found some exceptionally long distance foraging movements in high acorn crop years. The α-diversity values were significantly higher for Quercus lobata, but not for Quercus agrifolia, in years of high acorn production. We also found that different woodpecker family groups visited almost completely non-overlapping sets of source trees, and each particular group visited largely the same set of source trees from year to year, indicating strong territorial site fidelity.

Conclusions

Acorn woodpeckers forage in a pattern consistent with optimal foraging theory, with a few fascinating exceptions of long distance movement. The number of trees they visit increases in years of high acorn availability, but the extra trees visited are mostly local. The territorial social behavior of the birds also restricts their movement patterns to a minimally overlapping subsets of trees, but the median movement distance appears to be shaped more by the availability of trees with acorns than by rigid territorial boundaries.

【 授权许可】

   
2014 Thompson et al.; licensee BioMed Central Ltd.

【 图 表 】

Figure 1.

Figure 2.

Figure 3.

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