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First published online March 30, 2006
Journal of Experimental Biology 209, 1413-1420 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02138
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Kidnapping of chicks in emperor penguins: a hormonal by-product?

Frédéric Angelier1,*, Christophe Barbraud1, Hervé Lormée2, François Prud'homme1 and Olivier Chastel1

1 Centre d'Etudes Biologiques de Chizé, Centre National de la Recherche Scientifique, F-79360 Villiers en Bois, France
2 Office National de la Chasse et de la Faune Sauvage, F-79360 Villiers en Bois, France


Figure 1
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  		Fig. 1. Modelling kidnapping behaviour with a multi-state approach in the emperor penguin. States 1 and 2 are, respectively, the non-kidnapping state and the kidnapping state. {Psi}ab is the transition probability from state a to state b over one post treatment day (t) to the next one (t+1). {Psi}12 is the probability that a penguin will kidnap a chick from t to t+1. (1–S) is the probability that a bird will leave the colony from t to t+1. P and (1–P) are, respectively, the probabilities that a bird present on the colony in one of the behavioural state was seen or not during the daily scan.

 

Figure 2
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  		Fig. 2. Description of number of parameters (K) and AICc for various models testing for an effect of bromocriptine treatment on kidnapping behaviour in emperor penguins. Model 1 is the general starting model, with an effect of treatment and behavioural state on survival and sighting probabilities and an effect of treatment on transition probabilities. Model selection: an arrow starting from a model indicate the application of a constraint to this model. This constraint is detailed above the constrained model, which is at the end of the arrow. {Delta}AICc values were used to determine which model provides the best description of the data based on the fewest parameters ({Delta}AICc=AICc of the starting model–AICc of the constrained model). {Delta}AICc values >2 indicate that the constrained model is preferable. {Delta}AICc values <2 and >–2 indicate that models are fairly similar and the model including the fewest parameters was selected. {Delta}AICc values <–2 indicate that the starting model is preferable. Filled and broken arrows indicate, respectively, that the constraint was selected or not. Each model was defined using the following notations: S, survival probability; P, sighting probability; {Psi}ab transition probability from state a to b; 1, non-kidnapping state; 2, kidnapping state; {Psi}12br/{Psi}12co, {Psi}12 within the bromocriptine/control group; treatment/state: effect of treatment/behavioural state on a given parameter; prl: effect of initial level of PRL on a given parameter; {Psi}12first{Psi}122-7, effect of time since treatment on {Psi}12, which can vary between the first day and the last days of the study period. In models testing for an effect of PRL levels or time since treatment on {Psi}12 within one group (bromocriptine/control), {Psi}12treatment was dissociated and we used this notation {Psi}12br {Psi}12co. Models A and B are two nested models allowing us to test an effect of treatment on kidnapping behaviour during the first day of behavioural monitoring.

 

Figure 3
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  		Fig. 3. Estimates of the transition probability from the non-kidnapping to the kidnapping state for prolactin inhibited (bromocriptine, N=23) and control individuals (N=24), showing 95% confidence limits. Estimates were obtained from model 11 (Fig. 2).

 

Figure 4
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  		Fig. 4. Prolactin levels prior to the bromocriptine treatment for kidnappers (N=7) and non-kidnappers (N=16) within the bromocriptine group (mean ± 95% confidence limit).

 




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