Bruno J Ens

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment 1–4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions 1,5 , but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators 6–10. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring) 6–9,11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood 5–7,9. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization 12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within-and between-species diversity in incubation rhythms. Between species, the median length of one parent's incubation bout varied from 1–19 h, whereas period length—the time in which a parent's probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity 5–7,9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

... This estimate is based on 1) the empirical fact that most waders which had finished or suspended their body moult into summer plumage were heavy and thus ready to take off, and 2) the assumption that only the heaviest birds tn the population left, which allowed the mass of ...

Sinds 1990 is het aantal Scholeksters dat in Nederland broedt met 50% afgenomen. Een vergelijkbare afname van meer dan 40% heeft zich voorgedaan in het Waddengebied. Dit rapport beschrijft de resultaten van intensief bestudeerde en eveneens sterk afgenomen broedpopulaties van de Scholekster Haematopus ostralegus op Schiermonnikoog en Texel. Vanaf 1984 zijn in beide populaties elk jaar zoveel mogelijk dieren individueel gemerkt en zijn van alle dieren de overleving en het broedsucces bepaald. Met behulp van de gegevens over mortaliteit en reproductie is een simpel populatie model gebouwd. Het model is gebruikt om na te gaan welke parameter het meeste effect heeft op de groeisnelheid van de populatie en welke parameterverandering verantwoordelijk is voor de achteruitgang van de populatie.

A comparison of spring migration between three populations of Barnacle Geese Branta leucopsis using GPS satellite transmitters With the help of GPS technology it has recently become possible to track individual birds on migration in great detail. In this study we use GPS satellite transmitters to compare spring migration of three populations of Barnacle Goose in space and time: the Russian, Svalbard and Greenland populations. Populations differed in their migration patterns and stopover use, which can be related to differences in routes, in particular whether they had to cross any large-scale barriers during migration (Tab. 1, Fig. 1). Within populations, however, migration patterns also differed remarkably between individuals, especially in the Svalbard and Russian populations, with some individuals even ‘skipping’ stopovers altogether and flying ‘directly’ to the breeding grounds (Fig. 2). Within the Greenland population less variability was observed, possibly because these birds ...