- Massey University
Is plumage darkness in the North Island robin (Petroica longipes) mediated by aggression?
The extent of darkening of melanin-based plumages in birds has previously been linked with increasing aggressive encounters between individuals. The North Island robin (Petroica longipes) is a territorial New Zealand endemic passerine that displays delayed plumage maturation (darkening of the plumage with age). Aggressive boundary interactions in the robin are relatively common during the breeding season, when territories are protected and juveniles are dispersing. This study tests the hypothesis of aggression-mediated plumage darkening in a Population of North Island robins by examining if males and older (darker) birds are either (1) involved in a higher number of aggressive interactions, or (2) are more often the aggressor than females and younger birds. When sex and age are accounted for, darker individuals will be either (3) involved in a higher number of interactions or (4) more often the aggressor in encounters with other individuals. Data were collected by scoring the plumage darkness of 32 individuals in the field, and observing (1) interaction behaviours, and (2) age and sex of the birds involved in each interaction. The results show no support for any aggression-mediated plumage darkness in the robin; males and older birds were not involved in more aggressive interactions, and were not more often the aggressor; and neither the frequency were correlated with a darker plumage. Other more complex mechanisms may explain delayed plumage darkness in the North Island robin.
aggressiveness; DPM; delayed plumage maturation; melanin; North Island robin; Petroica longipes; plumage darkness; status-signalling
New Zealand Journal of Ecology
2008, Volume: 35, number: 4, pages: 331-334
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