Editor's choice - Common loon parents defend chicks according to both value and vulnerability

Submitted by Johan on 16 November 2015.

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Breeding is obviously a very important part in the life of organisms. However, the effort put into breeding need to be traded off against effort put into defense of the parents’ own soma. One often neglected part of parental effort is to protect young from predatory attacks.

Two different hypotheses were tested in an ingenious experimental set-up by Jukkala and Piper using breeding common loons (Gavia immer) as study subjects. Loon chicks are vulnerable to predation by conspecifics up to the age of 4 weeks. Jukkala and Piper set out to measure parental investment in protection of their young in relation to age of the young (vulnerability hypothesis) and in relation to brood size (value hypothesis). However, territorial intrusions by adult loons occur at a rate of 3 per day which would have made data collection tedious would this have been just an observational study. Instead they introduce an adult wooden decoy close to the adults of chicks and recorded the general behaviour of parents and specifically the incidence of yodels and penguin dances, both considered as behaviours to deter predatory attacks on chicks. They found that parents facing intruders stayed closer to their chicks, yodeled and performed penguin dances at higher frequencies when tending vulnerable chicks than when tending chicks old enough to be outside the predator window. Furthermore, they yodeled at higher frequencies when tending two chick broods compared to one chick broods. Thus, by this clever experimental set-up, the authors got support for both the vulnerability and the value hypotheses.

Jan-Åke Nilsson, Editor in Chief


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