Abstract
The choice of colony size may have profound consequences for individual fitness in colonially breeding birds, but at the same time it may require certain behavioural adaptations. Here, we aimed to examine behavioural divergence of common terns Sterna hirundo nesting in colonies of different size. For this purpose, we promoted establishment of small (<35 pairs) and large (>100 pairs) tern colonies under uniform ecological and environmental conditions by providing attractive patches of nesting substrate (floating rafts) at a single site. We combined video recording and GPS-tracking to assess communal and individual defence initiation rate, intra-specific aggression rate, and foraging flight characteristics. We found that birds from larger colonies more frequently engaged in communal defence and they performed longer foraging flights, while terns from smaller colonies more frequently showed individual defence behaviours. Also, intra-specific aggression rate was higher in smaller colonies, but this effect was primarily attributed to a higher proportion of edge breeding pairs, which were more aggressive. Our results suggest that various colony sizes may be associated with different behavioural syndromes, which comprise of diverse personality traits, such as social responsiveness, social tolerance, or propensity for aggression. It remains to be tested whether these behavioural differences reflect processes of phenotypic sorting among colonies of different size or whether they are a result of behavioural plasticity under different social contexts.
Highlights
Extraordinary variation in the size of avian reproductive groups has long perplexed ecologists and evolutionary biologists [1]
To test for non-linear patterns of diurnal variation in flight performance we entered squared hour as an additional covariate, but this effect was highly non-significant in each model and was excluded from the modelling. These linear models had similar fit to the general additive mixed models (GAMMs), where diurnal variation was modelled using non-linear smooth functions and, we reported the results of simpler general linear mixed models (GLMMs) models
We found that birds from larger colonies more frequently engaged in communal defence and they performed longer foraging flights, while terns from smaller colonies more frequently showed individual defence behaviours
Summary
Extraordinary variation in the size of avian reproductive groups has long perplexed ecologists and evolutionary biologists [1]. Avian colonies vary greatly in size between- and within-species, spanning several orders of magnitude in many taxa [2]. Some species are facultatively colonial, as they can breed solitarily or in aggregations depending on habitat and geographical location, while others can change from solitary to colonial breeding in consecutive years [3, 4]. It is generally agreed that colony size is an evolutionarily labile trait with weak phylogenetic signal, it shows some species-specificity [5, 6].
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