Niche switching and leapfrog foraging: movement ecology of sympatric petrels during the early breeding season
Résumé
Background: The timing of events in the early part of the breeding season is crucially important for successful
reproduction. Long-lived animals that migrate large distances independently of each other meet at the breeding
sites to re-establish their pair bonds and coordinate their breeding duties with their partners.
Methods: Using miniature light-geolocation and immersion data together with blood stable isotopes, we studied
the early breeding season in Thin-billed prions Pachyptila belcheri, Antarctic prions P. desolata and Blue petrels
Halobaena caerulea breeding at Kerguelen Islands in the Indian Ocean. These three species exhibit differences in
their winter habitat and timing of migration, moult and breeding. We hypothesised that these differences would
influence their behaviour during the early breeding season.
Results: In line with our hypothesis, we found clear differences not only in the timing of colony attendance, but
also in the time budgets while at sea and in habitat use. Both early breeding Blue petrels and late breeding Antarctic
prions spent about 8 h per day in flight and 15 h foraging. In comparison, Thin-billed prions, which breed in midsummer,
spent less time (5 h daily) in flight and more time (18 h daily) foraging, thus maximizing the time spent
foraging during the longest daylight days of the year. While the ecological habitat parameters (sea temperature, wind,
productivity) of Thin-billed prions and Blue petrels were relatively stable throughout the year, Antarctic prions showed
clear niche switching, caused by leapfrogging between the northernmost winter distribution to the southernmost
distribution during the early breeding season. Blood stable isotopes confirmed the habitat switch between the interbreeding
and early breeding periods and highlighted trophic segregation with Blue petrels feeding more on fish and
Antarctic petrels more on crustaceans during the early breeding period.
Conclusion: We found that the three sympatric petrel species segregated in time and space, both in the winter and
the early breeding season. The interplay of timing and distribution meant that the three species show the full range of
migratory strategies, from niche-tracking Blue petrels to niche-switching Antarctic prions. The latitudinal distribution
resembled the leapfrogging of terrestrial avian migrant species or populations.