Winter areas and migratory tactics of northern gannets (morus bassanus) breeding in North America

Fifield, David A. (2011) Winter areas and migratory tactics of northern gannets (morus bassanus) breeding in North America. Masters thesis, Memorial University of Newfoundland.

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Abstract

Migration has evolved to allow organisms to undertake life history functions in the most appropriate place at the most appropriate time. Migration creates seasonal ecological linkages that have important implications for survival, population dynamics, response to climate change and species conservation. Yet, knowledge of the wintering areas, migratory routes and timing of migration for individual and populations are unknown for most avian species, particularly seabirds. -- This is the first study to electronically track migration and wintering of gannets breeding in North America. Data from band returns and geolocators were integrated to investigate migratory connectivity and the timing and execution of migration in Northern Gannets (Morus bassanus) from four large North American colonies. -- Gannets had distinct wintering areas and aggregated into several major hotspots. Most adults remained along the northeast North American coast closest to their colonies and breeding populations displayed weak migratory connectivity. Unexpectedly, the Gulf of Mexico was revealed to be an important wintering area for adults. Gannets displayed remarkable winter site fidelity with extensive range overlap across years. -- Timing, rates of movement and use of stopovers during migration depended strongly upon winter destination and also upon sex, colony and year. Females departed the colony prior to males in fall but, contrary to prediction, earlier spring arrival of males was not detected. Variation in the ecological constraints operating during different seasons was emphasized by faster and shorter spring migrations in comparison to fall migrations. The repeatability of migratory duration, distance, and timing of arrival and departure from the winter grounds suggested strong individual programs for these traits. However, variability in the timing of colony departure and arrival, migratory speed, and the extent of stopovers en route implies greater involvement of environmental inputs into these behaviours. -- This is the first study to report two strikingly different migration strategies involving trans-Atlantic migration in a continental-shelf migrant seabird. Three gannets displayed a radically different migration and over-winter strategy by undertaking the first recorded (and repeated), wind-assisted, round-trip trans-Atlantic migrations to the coast of Africa, crossing the Atlantic Ocean in as little as five days. The departure timing and routes of west-to-east (and to a lesser extent east-to-west) oceanic crossings were adjusted to maximise the assistance of winds generated by large weather systems; indicating the use of choice in the execution of this remarkable feat for a normally continental shelf migrant. The discovery of this trans-Atlantic connection has implications for interaction, connectivity and phylogeographic radiations between the eastern and western Atlantic populations. -- The observed patterns of migratory timing and scale-dependent connectivity present a novel opportunity to assess the ecological and conservation implications of specific threats during migration and on the wintering grounds. The lability of migratory tactics in the population as a whole combined with remarkable individual consistency in some, but not all, migration parameters offer rare insight into the relative contributions of genetic and environmental factors controlling migration.

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