Bautista, L.M., J.C. Alonso and J.A. Alonso. 1995. A field test of ideal free
distribution in flock-feeding common cranes. J. Anim. Ecol. 64:747-757.
Summary. 1. The densities of common cranes Grus grus in 10 zones of a wintering
area were approximately proportional to the amounts of food resources, but some
overuse of the zones with highest food densities was observed, i.e., greater
numbers of birds than expected used these zones. The distribution resembled
ideal free distribution only after numbers of cranes had exceeded carrying
capacity. The seasonal pattern of settlement deviated from ideal free
distribution. During the early and late part of the season, when there were
fewer birds at the study site, cranes preferred to forage as close to the roost
as possible provided that there was enough food, instead of selecting the zones
further away with highest food densities.
2. However, 12 individually marked cranes differed in their competitive
ability and foraging area selection. Larger adult birds were dominant in
aggressive encounters, displacing subdominant cranes from good feeding
positions. Food intake rate of dominant cranes tended to be higher than the flock
average, the difference increasing with rank. Dominant cranes preferred to
forage in the zones with highest food densities and had higher absolute daily
food intakes. The relative pay-offs of different phenotypes changed across
zones with different food densities: subordinate birds could not increase their
intake rate at the richest zones as much as dominants.
3. The average daily food intake of a crane was thus positively correlated with
both the quality of the foraging zone and the dominance rank of the bird. These
results fulfil most assumptions and predictions of the interference
phenotype-limited distribution model, although truncation of phenotypes between
zones was imperfect.
Reprinted from the Journal of Animal Ecology published by The British Ecological Society, copyright ©
1998 by Blackwell Science Ltd.. All rights reserved.This text may be used and
shared in accordance with the fair use provisions of UK and international
copyright law and agreement, and it may be archived and redistributed in
electronic form, provided that this entire notice, including copyright
information, is carried and provided that Blackwell Science Ltd is notified and
no fee is charged for access. Archiving, redistribution or republication of
this text on other terms, in any medium, requires both the consent of the
author(s) and The British Ecological Society.