Evol Ecol Res 10: 811-822 (2008)     Full PDF if your library subscribes.

Acorn harvesting by acorn woodpeckers: annual variation and comparison with genetic estimates

Walter D. Koenig, Jay P. McEntee and Eric L. Walters

Hastings Reservation and Museum of Vertebrate Zoology, University of California, Berkeley, Carmel Valley, California, USA

Correspondence: W.D. Koenig, Laboratory of Ornithology and Department of Neurobiology and Behavior, Cornell University, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA.
e-mail: wdk4@cornell.edu

ABSTRACT

Questions: (1) How does the effort that birds invest in harvesting acorns, including the distance the acorns are moved – a key factor affecting population structure of the trees – covary with the size of the acorn crop? (2) How well are harvest patterns, previously inferred by indirect, genetic methods, matched by data from direct observations of harvesting?

Organisms: The acorn woodpecker (Melanerpes formicivorus), a cooperatively breeding species that is highly dependent on acorns, which are stored in specialized storage trees known as granaries.

Methods: We observed acorn harvesting over 4 years at Hastings Reservation in central coastal California, a period over which acorn crops varied considerably in size.

Results: Birds harvested 94% of acorns from a small number of trees located within 150 m of their granary. The distances travelled by birds to harvest acorns and the number of trees from which acorns were harvested were both greater in a poor acorn year than when the crop was good. Birds did not necessarily prefer the species of acorn that was most abundant. The distance birds travelled to harvest acorns, harvesting overlap among groups, and the number of trees from which acorns were harvested generally matched the findings of Grivet et al. (2005), indicating that an indirect genetic approach can be effective when direct observation of seed dispersal is difficult.

Keywords: acorn woodpecker, caching behaviour, dispersal, foraging strategy, Melanerpes formicivorus, oaks, seed movement.

DOWNLOAD A FREE, FULL PDF COPY
IF you are connected using the IP of a subscribing institution (library, laboratory, etc.)
or through its VPN.

 

        © 2008 Walter D. Koenig. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

       Subscribing institutions/libraries may grant individuals the privilege of making a single copy of an EER article for non-commercial educational or non-commercial research purposes. Subscribing institutions/libraries may also use articles for non-commercial educational purposes by making any number of copies for course packs or course reserve collections. Subscribing institutions/libraries may also loan single copies of articles to non-commercial libraries for educational purposes.

       All copies of abstracts and articles must preserve their copyright notice without modification.