Investigator disturbance while monitoring seabirds can result in lower survival rates and breeding success, leaving lasting negative impacts on the population and biasing observations. For example, monitoring rhinoceros auklets ( Cerorhinca monocerata ) and other burrowing alcids can reduce breeding success or even survival through handling stress and damage to nesting habitat. For this reason, researchers must seek to decrease colony disturbance. Automated radio-frequency identification (RFID) via passive integrated transponder (PIT) tags is an inexpensive and reliable way to identify individual presence and record attendance behaviour, avoiding the need to recapture seabirds or visit the colony frequently. PIT tags either can be implanted subcutaneously or attached externally to leg bands, but it is unclear which method causes lower disturbance. To examine the impact of PIT tagging on rhinoceros auklets nesting in artificial burrows on Middleton Island, Alaska, we monitored burrow entrances with automated recording RFID readers to collect presence and nest attendance data. PIT-tagged (either band attachment or subcutaneous implant) and control birds had similar breeding success and chick growth rates. Breeding success was similar between nests with one or two parents marked. Birds tagged externally were detected less often than birds marked with a subcutaneous implant. We conclude that PIT tagging of rhinoceros auklets is a relatively non-invasive method for seabird monitoring, and that subcutaneous implants do not cause more disturbance than external attachment.

Which factors shape animals' migration movements across large geographical scales, how different migratory strategies emerge between populations, and how these may affect population dynamics are central questions in the field of animal migration [1] that only large-scale studies of migration patterns across a species' range can answer [2]. To address these questions, we track the migration of 270 Atlantic puffins Fratercula arctica, a red-listed, declining seabird, across their entire breeding range. We investigate the role of demographic, geographical, and environmental variables in driving spatial and behavioral differences on an ocean-basin scale by measuring puffins' among-colony differences in migratory routes and day-to-day behavior (estimated with individual daily activity budgets and energy expenditure). We show that competition and local winter resource availability are important drivers of migratory movements, with birds from larger colonies or with poorer local winter conditions migrating further and visiting less-productive waters; this in turn led to differences in flight activity and energy expenditure. Other behavioral differences emerge with latitude, with foraging effort and energy expenditure increasing when birds winter further north in colder waters. Importantly, these ocean-wide migration patterns can ultimately be linked with breeding performance: colony productivity is negatively associated with wintering latitude, population size, and migration distance, which demonstrates the cost of competition and migration on future breeding and the link between non-breeding and breeding periods. Our results help us to understand the drivers of animal migration and have important implications for population dynamics and the conservation of migratory species.