1365-2656/asset/olbannerleft.gif?v=1&s=4f0919eca9042f833d018453e8f48b1e3e3123ec)
1365-2656/asset/olbannerright.gif?v=1&s=92164cf20561f2dc5785bff8431569e5b40f87aa)
You have full text access to this OnlineOpen article
Search paths of swans foraging on spatially autocorrelated tubers
Article first published online: 8 MAY 2002
DOI: 10.1046/j.1365-2656.2002.00610.x
1365-2656/asset/cover.gif?v=1&s=e1c445961d632cd41e33852af907c4900097559b "Journal of Animal Ecology")
Additional Information
How to Cite
Nolet, B. A. and Mooij, W. M. (2002), Search paths of swans foraging on spatially autocorrelated tubers. Journal of Animal Ecology, 71: 451–462. doi: 10.1046/j.1365-2656.2002.00610.x
Publication History
- Issue published online: 8 MAY 2002
- Article first published online: 8 MAY 2002
- Received 16 July 2001; revision received 4 January 2002
- Abstract
- Article
- References
- Cited By
Keywords:
- area-restricted search;
- correlated random walk;
- Cygnus columbianus bewickii;
- depletion;
- Potamogeton pectinatus
Summary
- 1Tundra swans forage on below-ground pondweed tubers that are heterogeneously distributed in space. The swans have no visual cues to delineate patches. It was tested whether swans employ an area-restricted search tactic. Theory predicts that swans should alternate between an intensive (low-speed, sinuous) search mode in high tuber density areas and an extensive (high-speed, directed) search mode between these areas.
- 2A quantitative analysis of movement paths recorded over short time frames (15 min) revealed that the sequential step lengths were strongly autocorrelated. After partitioning the data in low-speed paths and high-speed paths, this autocorrelation was very much reduced.
- 3Movement paths with low speed were non-directional and could well be described as random walks. In contrast, high-speed paths were directed forward, and were better described as correlated (i.e. directional) random walks.
- 4Movement paths recorded over longer time frames (1–4 h) provided empirical evidence that an alternation of low-speed, sinuous and high-speed, directed searches occurred.
- 5There was a spatial autocorrelation in tuber biomass density, being significantly positively correlated until c. 10 m distance. The scale of the food clump size and step length of high-speed paths matched, suggesting that they were causally linked.
- 6Computer simulations confirmed that swans using the observed search tactic achieved a higher energy gain than swans using only an intensive search mode, provided that the tuber biomass density occurred in clumps. They also achieved a higher gain than swans that alternated between intensive and extensive search mode, but always moved in a random direction.