Reaching independence: food supply, parent quality, and offspring phenotypic characters in kestrels

Auteurs: Pablo Vergara, Juan A. Fargallo, Jesus Martinez-Padilla
Bron: BEHAVIORAL ECOLOGY, 2010 21(3):507-512; doi:10.1093/beheco/arq011
Abstract: The duration of the postfledging dependence period (PFDP) is supposed to be modulated by the parent offspring conflict: Offspring should extract the highest levels of parental investment, although parents may respond by setting fixed limits to the level of investment or by raising the costs of attempts to extract additional investment. In this context, longer PFDPs are expected in nests tended by higher quality parents and in dominant siblings. We explored these hypotheses with a combination of experimental and correlative results. First, we food supplemented offspring during the PFDP to study whether food supply during fledging, an indicator of parental quality, has an effect on the PFDP duration in the Eurasian kestrel. We found that the PFDP was longer in food-supplemented nests. Second, we measured the duration of the PFDP over 3 years under different environmental conditions to explore whether the quality of parents and nestling phenotype were correlated with the duration of PFDP. Correlative results suggest that fledglings raised by higher quality parents and in the year with poorer food conditions showed longer PFDP. Furthermore, male fledglings showing grayer coloration in the rump (an index of competitive capacity) have longer PFDPs than browner males. Overall, our results suggest that parent, rather than offspring characteristics, can modulate the PFDP duration mediated by food conditions, although more colored nestlings stay in the nest territory for longer periods.

Dutch Wadden Sea May Become Bottleneck for Wading Bird

The Dutch Wadden Sea, due to a decline in food resources, may become a bottleneck in the annual cycle of a wading bird known as the knot.

This has been revealed by PhD research by Casper Kraan. He studied two subspecies of the knot, the Calidris canutus islandica and the Calidris canutus canutus.

"It appears that neither species is able to fatten up properly in the Wadden area any more," says Kraan. He conducted his research at the Royal Netherlands Institute for Sea Research (NIOZ) and will be awarded a PhD by the University of Groningen on 26 April 2010.

The islandica breeds on the Canadian and Greenland tundra and then flies to the Wadden area to overwinter. The canutus breeds in Siberia and uses the Wadden Sea to fatten up for the last stage to western Africa. Kraan: "Although the two subspecies have different strategies, they have the same problem -- declining food resources."

Lees meer: Science Daily

Preservation of winter social dominance status in Brent Geese Branta bernicla bernicla within and across winters

Auteurs: Maud Poisbleau, Noel Guillon, Herve Fritz
Bron: JOURNAL OF ORNITHOLOGY, DOI 10.1007/s10336-009-0437-8
Abstract: Dominant and subordinate individuals in a group may benefit from the stability of the social dominance organisation, avoiding excessive waste of time and energy in aggressive interactions and reducing injury risks. Nevertheless, the likely evolutionary incentive for individuals to become, and furthermore to stay, dominant may destabilise such dominance hierarchies. In this context, the relative importance of fixed (e.g. sex, morphological size) and fluctuating (e.g. body condition, mating status, reproductive success, social unit size) traits influencing the establishment and preservation of dominance relationships could play a key role in group structure. We investigated the relative role of fixed and fluctuating traits on social status in Dark-bellied Brent Geese Branta bernicla bernicla which form large fairly unstable groups both within and across winters. We compared individual dominance scores of ringed Brent Geese during four consecutive winters. Brent Geese conserved their dominance score within a given winter irrespective of their age but were generally unable to conserve it across consecutive winters. As winter dominance scores correlated best with social unit size, dominance status thus appeared to be mostly a by-product of a fluctuating trait: breeding success in the previous summer. When we considered only adults that had the same social unit size during two consecutive winters, we observed a significant preservation of dominance scores. This result suggests that a fixed trait such as sex or morphological size may still play a role in setting dominance status.