Authors: Martin Bulla, Mihai Valcu, Adriaan M. Dokter, Alexei G. Dondua, András Kosztolányi, Anne L. Rutten, Barbara Helm, Brett K. Sandercock, Bruce Casler, Bruno J. Ens, Caleb S. Spiegel, Chris J. Hassell, Clemens Küpper, Clive Minton, Daniel Burgas, David B. Lank, David C. Payer, Egor Y. Loktionov, Erica Nol, Eunbi Kwon, Fletcher Smith, H. River Gates, Hana Vitnerová, Hanna Prüter, James A. Johnson, James J. H. St Clair, Jean-François Lamarre, Jennie Rausch, Jeroen Reneerkens, Jesse R. Conklin, Joanna Burger, Joe Liebezeit, Joël Bêty, Jonathan T. Coleman, Jordi Figuerola, Jos C. E. W. Hooijmeijer, José A. Alves, Joseph A. M. Smith, Karel Weidinger, Kari Koivula, Ken Gosbell, Klaus-Michael Exo, Larry Niles, Laura Koloski, Laura McKinnon, Libor Praus, Marcel Klaassen, Marie-Andrée Giroux, Martin Sládeček, Megan L. Boldenow, Michael I. Goldstein, Miroslav Šálek, Nathan Senner, Nelli Rönkä, Nicolas Lecomte, Olivier Gilg, Orsolya Vincze, Oscar W. Johnson, Paul A. Smith, Paul F. Woodard, Pavel S. Tomkovich, Phil F. Battley, Rebecca Bentzen, Richard B. Lanctot, Ron Porter, Sarah T. Saalfeld, Scott Freeman, Stephen C. Brown, Stephen Yezerinac, Tamás Székely, Tomás Montalvo, Theunis Piersma, Vanessa Loverti, Veli-Matti Pakanen, Wim Tijsen & Bart Kempenaers
Brief summary of the paper: The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators.
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). The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood.
Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization 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. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.