To test a central hypothesis within predator-prey relations, breeding success and chick survival in black-legged kittiwakes and Brünnich’s guillemots in two SEAPOP key sites were compared with corresponding data for Antarctic petrels in Dronning Maud Land. The results show that synchronized hatching is advantageous for colonial seabirds in the presence of a specialized predator.

Strength in numbers

According to the so-called “predator swamping” hypothesis, reproductive synchrony in a prey species will only be advantageous if the predator posing the main threat towards eggs and chicks specializes on this prey. The mechanism behind this is that the predator becomes overwhelmed by the sudden increase of available chicks in the colony and will therefore not be able to catch them and feed them to its own chicks as effectively as it would if the hatching was more evenly spread throughout the season. Following this hypothesis, synchronous breeding may not be an advantage in the presence of a generalist predator, as a huge number of available eggs and chicks may change the behaviour of the predator towards specialization on this prey. On the other hand, asynchronous breeding will not make a large number of chicks available at the same time, and the predator will remain a generalist. A scientific article from the Norwegian Polar Institute presents how this hypothesis was tested by comparing chick survival in Brünnich’s guillemots and black-legged kittiwakes on Svalbard with the survival of Antarctic petrel chicks at Svarthamaren in Dronning Maud Land.

The south polar skuas breeding near Svarthamaren in Dronning Maud Land have specialized in preying on eggs and chicks of the Antarctic petrel, the only prey available.
Photo: Sébastien Descamps, Norwegian Polar Institute

Support to the hypothesis

The guillemot and kittiwake nests monitored in the study were preyed upon by glaucous gulls and to some extent by Arctic foxes – both generalist species that feed on a wide range of prey. The Antarctic petrels at Svarthamaren, on the other hand, are threatened by a highly specialized predator, the south polar skua. The hatching of the Antarctic petrels, which were monitored in four different breeding seasons, was highly synchronous, and chicks hatching close to the average hatching date had a higher survival rate than others. In the Brünnich’s guillemots and kittiwakes monitored on Svalbard, hatching was less synchronous, and there was no apparent fitness advantage related to hatching close to the average hatching date. The findings in this study support the predator swamping hypothesis and emphasizes the potential importance of the timing of reproduction for the seabird chicks to survive.

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Contact person: Sébastien Descamps, Norwegian Polar Institute