Great Crested Grebe (Podiceps cristatus) synchronies egg laying with protective species

Abstract

Great crested grebes (Podiceps cristatus) are opportunistic breeders nesting in colonies or solitarily in different biotopes with varying nesting dates in different circumstances. On the northern coast of the Neva Bay in the eastern part of the Gulf of Finland, great crested grebes breed solitarily, in colonies situated in reed beds and in a colony on the open water in direct vicinity of a colony of black-headed gulls (Larus ridibundus) and black terns (Chlidonias niger). In the vicinity of the larid colony, grebes profit from the protecting behaviour of gulls and terns in a similar way as they do in their mixed colonies with larids. Despite the fact that small larids have a shorter incubation period than great crested grebes, the latter synchronize their beginning of incubation with the gulls and terns. The incubation of all three species in two adjoining open-water colonies started on the same dates. The incubation of grebes nesting in the reed beds began significantly later. The average clutch sizes did not differ significantly between the colonies situated on the open water near larids and those in the reeds. The average lowest distances between the nests of great crested grebes in the open water colony were larger than in the reed bed colonies. The ability to synchronize the beginning of incubation with a small protecting species helps great crested grebes to occupy otherwise unsafe habitats.

Comparison of spring and summer clutches of Great Crested Grebes (Podiceps cristatus)

“…Compared to spring nests, where "colonial" behaviour was detected as the main factor of clutch size, in summer nests the location concerning the edge of littoral vegetation was found to be most important (the distance from shoreline explains 36% of the variability of clutch size). Our result could be in line with the findings of Zaynagutdinova and Mikhailov (2019), who found that pairs nesting on open water started incubation earlier than pairs in reed stands. Later nesting was also found by Bukacinska et al (1993) for non-colonial nesting pairs.…”

“…This happens mainly through two mechanisms: variable clutch size and asynchronous hatching (Vlug 2005). Changes in reproductive behaviour are also linked with changes in the nesting environment (Marxmeier & Duettmann 2002, Zaynagutdinova & Mikhailov 2019.…”

“…Interestingly, when a pair loses eggs or young, substitute clutches are laid (Cramp 1985, Konter 2007. Average clutch size is known to vary significantly, also dependent upon the specific characteristics of the nest location (Zaynagutdinova & Mikhailov 2019). Bukacinska et al (1993) observed the effects of the season when egg laying took place and proximity to a colony on nesting parameters for Great Crested Grebes on Luknajno Lake in northeast Poland.…”