Coexistence of two sympatric migratory shearwater species during their non-breeding season on the east coast of Newfoundland
Loading...
Date
2018-12-06
Authors
Paloma, Calabria Carvalho
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
In the marine environment, prey aggregations are not uniformly distributed, which drives predator species to aggregate in specific areas of high food availability. When multiple species aggregate to forage, interspecific competition can occur if prey are limited. On the east coast of Newfoundland, a small forage fish, capelin (Mallotus villosus), move inshore to spawn during the summer, and become the main prey for most marine predators in the study area. During the same period, non-breeding seabirds, great and sooty shearwaters (Ardenna gravis and A. grisea), migrate and aggregate in coastal Newfoundland. I investigated how these two similar shearwaters species coexist during the summer (July and August) under varying capelin availability. Based on at-sea surveys, great and sooty shearwaters were highly associated with each other and typically distributed along the coast in shallow waters (< 50 m) at or nearby capelin spawning sites. Stable isotope ratios (δ13C and δ15N) from the blood and primary feathers moulted in the study area showed that both species were also feeding on similar prey types, with high isotopic niche overlap. Behavioural experiments examining species interactions during prey capture, however, revealed that great shearwaters displayed more bold and aggressive behaviour compared to sooty shearwaters. Additionally, stable isotope ratios of both primary feathers (P1 and P5) moulted prior to arrival in coastal Newfoundland differed between species and sooty shearwaters had an advanced stage of moult compared to great shearwaters upon arrival, both suggesting temporal and spatial segregation during early moult. In conclusion, both species share a similar annual cycle and feed on similar prey while using coastal Newfoundland to complete their moult and replenish body storages before southward migration to the breeding grounds. However, subtle differences in foraging behaviour to capture prey were observed, revealing how these species can coexist while using the same resources at the same location and time.
Description
Keywords
Niche partitioning, Stable isotope, Niche overlap, Moult, Shearwater, Competition, Newfoundland, Coexistence