image: Between-species variation in incubation rhythms in shorebirds with cryptic behavior (on the left) and without it (on the right). view more
Credit: Pavel Tomkovich
An international research group, including a scientist from the Zoological Museum (Faculty of Biology, Lomonosov Moscow State University) has conducted a comparative analysis of incubation rhythms in a range of shorebird species with wide geographical coverage. This became possible due to usage of light loggers (geolocators). The results of the project have been published in Nature. Part of the study fulfilled in the Lomonosov Moscow State University has been conducted within the framework of the "Noah's ark" project.
Pavel Tomkovich, a Leading Researcher (Zoological Museum at the Faculty of Biology, Lomonosov Moscow State University) together with Egor Loktionov has made the following contribution to the project. They have shared the data about shorebird incubation rhythms, obtained in southern Chukotka from geolocators retrieved from breeding lesser golden plovers (Pluvialis fulva), common ringed plovers (Charadrius hiaticula) and red knots (Calidris canutus). They also presented data on nests, incubating birds and their behavior (namely, the human approach response). Geolocators' readings were checked by direct observations, made during studies of incubation modes in red knots.
Pavel Tomkovich, Doctor of Biological Sciences from the Lomonosov Moscow State University, and one of authors of the paper, says: "This study is devoted to learning about the organization of our world, where we live together with the plants and animals. It seems that this project doesn't have direct practical application. For ornithologists this study helps to understand how birds react to some environmental variables, such as light conditions, tidal effects on the sea shores (where shorebirds forage) and temperature conditions. It also reveals why nests of some species can easily be found, while in case of other species, on the contrary, it is extremely difficult."
The research is based on data collected by zoologists from many countries on different continents, who directly and remotely studied various species of shorebirds during nesting period with the help of the methods of instrumental control (video cameras, geolocators, GPS and radio tags).
Geolocators or light sensors, being fixed to a ring placed on a bird's leg, record in the memory unit of the device its light intensity, with the frequency of 5 or 10 minutes. This approach has allowed to determine periods of continuous coverage of a clutch of eggs (when a geolocator is closed by the bird's body and feathters) and periods of activity outside the nest (when a geolocator is mostly lit).
It is necessary to retrap a bird with a geolocator in order to download the stored information from this mini device. Interpretation of this piece of data allows to understand incubation rhythms of the bird, namely about the length of periods of continuous incubation and incubation cycles both during a day and the whole period of incubation: from egg laying till chick hatching.
A comparative analysis for a wide range of species with wide geographical coverage only became possible thanks to the agglomeration of data obtained by a multitude of researchers. Data about incubation rhythms from 729 nests of 91 populations of 32 monogamous biparentally incubating shorebird species are used for comparisons in this study.
Researchers have shown significant within and between-species diversity in behavioral rhythms' synchronization of incubating mates. The mean value length of one parent's incubation bout on average varied from 1 to 19 hours. And the probability of the length of one incubation cycle alternately by each mate was fluctuating from 6 to 43 hours. The length of incubation bouts didn't depend on energy cost indicators. This characteristic was more sustainable among species that rely on crypsis (a type of coloration that enables a bird to avoid detection by other animals), in comparison with the species that are readily visible or actively defend their nest from predators.
Rhythms, entrainable to the 24-h light-dark cycle, are less prevalent at high latitudes, being absent in 18 species. The similarity of incubation rhythms among closely related species has been discovered. Even in the same environmental conditions, including the 24-h light-dark cycle, social synchronization of partners' behavioral rhythms is much more diverse than it has been expected, judging by the results of observations conducted in captivity.
Scientists have come to a conclusion that the risk of egg loss from predators (and not the risk of starvation of an incubating bird, which doesn't get food) could be a key factor that determines the observed diversity in incubating rhythms.
Pavel Tomkovich notices: "In science some questions are always left... In the current case it is quite obvious that further clarifications are needed. It is still necessary to learn whether the length of incubation bouts of shorebirds with cryptic nest behavior depends on predators' pressure. Besides that, it is still unclear how the existing diversity in incubation rhythms has emerged and which consequences one or another incubation rhythm has for th partners (for instance, concerning energy demand)."
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Journal
Nature