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1 April 2009 Foraging Site Selection of Two Subspecies of Bar-tailed Godwit Limosa lapponica: Time Minimizers Accept Greater Predation Danger Than Energy Minimizers
Sjoerd Duijns, Jacintha G.B. van Dijk, Bernard Spaans, Joop Jukema, Willem F. De Boer, Theunis Piersma
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Abstract

Different spatial distributions of food abundance and predators may urge birds to make a trade-off between food intake and danger. Such a trade-off might be solved in different ways in migrant birds that either follow a time-minimizing or energy-minimizing strategy; these strategies have been assigned to two sub-species of Bar-tailed Godwits Limosa lapponica that use the European Wadden Sea during northward migration. At the study area on Terschelling we recorded feeding site selection, time budgets and intake rates (prey/min) in the period that both lapponica (energy minimizer) and taymyrensis (time minimizer) sub-species were present (late April till the end of May 2007). Prey availability (number of prey/m2) was negatively correlated to the distance from cover. Based on resightings of colour-ringed Bar-tailed Godwits, taymyrensis was foraging closer to cover, and for a higher proportion of time than lapponica (67% vs. 33%). During the high tide period taymyrensis was also foraging on inland coastal meadows, Moreover, taymyrensis was more vigilant than lapponica, whereas lapponica showed more resting and preening behaviour. Lapponica had a higher instantaneous intake rate, but taymyrensis had a higher overall intake rate and the birds were more successful in taking larger prey items than lapponica. Supposedly, due to the increased foraging time and additional foraging on the inland meadows, the time-minimizing taymyrensis achieved a higher fuel deposition rate than lapponica. Taymyrensis shifted towards food-rich areas, apparently accepting higher predation risks, whereas energy-minimizing lapponica avoided predation danger by foraging further from cover.

Sjoerd Duijns, Jacintha G.B. van Dijk, Bernard Spaans, Joop Jukema, Willem F. De Boer, and Theunis Piersma "Foraging Site Selection of Two Subspecies of Bar-tailed Godwit Limosa lapponica: Time Minimizers Accept Greater Predation Danger Than Energy Minimizers," Ardea 97(1), 51-59, (1 April 2009). https://doi.org/10.5253/078.097.0107
Received: 19 July 2008; Accepted: 1 September 2009; Published: 1 April 2009
KEYWORDS
feeding site selection
intake rate
Limosa lapponica lapponica
Limosa lapponica taymyrensis
migration strategy
predation
trade-off
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