![]() ![]() Moreover, Coulson & White (1960) found an effect of neighbour density rather than colony size on synchrony in kittiwakes ( Rissa tridactyla). However, this is difficult to reconcile with the fact that often close neighbours and sub-colonies are more synchronized than the whole colony ( Burger 1979 Thomas 1986 Murphy & Schauer 1996 Mougin et al. Second, within the same population of a bird species, different colonies or sub-colonies can be strongly synchronized themselves but considerably out of phase with other nearby colonies or sub-colonies ( Coulson & White 1960 Burger 1979).īoth Darling's hypothesis and environmental factors focus on the scale of the entire colony or even larger scales. First, even within different colonial species breeding in the same place and feeding on the same prey, the degree of breeding synchrony can be very different ( Reed et al. But empirical evidence is not compatible with this hypothesis. Darling (1938) himself presented some data confirming a positive effect of colony size on synchrony, but later reanalyses of these data revealed statistical problems, and further data from other species showed no consistent pattern (reviewed by Gochfeld 1980).Īn alternative to Darling's hypothesis would be that environmental factors such as day length, temperature or food availability trigger breeding synchrony. of the cumulative value of stimulation) on synchronization remains unclear. 2007) and provide evidence of the endocrine mechanisms of social stimulation ( Ball & Bentley 2000 Wingfield et al. Some empirical studies support these predictions (Waas et al. More synchronous breeding is thus expected under the stronger social stimulation occurring in larger colonies. ![]() In any case, these ultimate explanations cannot inform us about the proximate mechanisms leading to breeding synchrony in the first place, which are the focus of this paper.ĭarling (1938) proposed a proximate mechanism for synchrony: non-breeding birds in a colony are stimulated by the cumulative value of the voice, and the presence of the breeding members of the colony to start breeding themselves. Coulson (2002) suggested that these advantages are consequences rather than (adaptive) causes of breeding synchrony. ![]() However, empirical tests of these hypotheses are inconclusive, suggesting that the advantages of synchronized breeding could either be case specific or occur in different combinations, or even that synchrony can be maladaptive ( Gochfeld 1980 Wittenberger & Hunt 1985). Different ultimate explanations of colony synchrony have been proposed, including predation satiation, mate finding, reduction of intraspecific interactions and formation of juvenile flocks ( Darling 1938 Emlen & Demong 1975 Yom-Tov 1975 Nelson 1980 Mougin et al. We argue that collective patterns such as breeding synchrony in colonial birds could have simple adaptive individual-level explanations.īreeding synchrony is a characteristic of colonial birds-female birds in a colony are often at a strikingly similar breeding stage: laying eggs incubating or feeding similarly aged chicks ( Gochfeld 1980 Nelson 1980 Coulson 2002). Our study highlights the power of local adaptive (individual) behaviour to create global (colony) patterns. Moreover, females bred in a safer environment, which is known from field studies to increase fitness. Even giving only a low relevance to the neighbour's stress level was enough to synchronize the laying date of neighbours and also of a huge colony. A female laid her eggs when her stress level fell to a critical value. We tested our hypotheses using a generic individual-based model where the breeding predisposition of females was updated daily depending on an increase in the photoperiod (positively) and the stress level of neighbours: negatively if they were agitated, and positively otherwise. Moreover, we propose that this local process, together with environmental cues, can synchronize breeding between neighbours and through a whole colony. We propose that social tranquillity at the time of laying can be achieved if a bird's stress level is partly determined by the agitation of its neighbours. In colonies, conspecific birds often destroy eggs and kill chicks, either intentionally or not. Why and how birds in colonies often breed in striking synchrony is an unsolved question. ![]()
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