At-sea activity of Black-legged kittiwakes (Rissa Tridactyla) reveals dispersal strategies and exposure to anthropogenic pressures

Until recently, knowledge of seabirds has been rather restricted to the breeding season, yet pressures during the nonbreeding season may significantly impact seabird breeding success and population demographics. Furthermore,... [ view full abstract ]

Until recently, knowledge of seabirds has been rather restricted to the breeding season, yet pressures during the nonbreeding season may significantly impact seabird breeding success and population demographics. Furthermore, the nonbreeding season is a time in the life cycle to replace feathers and restore energy reserves, during which seabirds can be vulnerable to anthropogenic pressures. This study tracked black-legged kittiwakes Rissa tridactyla from Isle of Canna, Scotland, using combined geolocators and wet-dry sensors to better understand dispersal patterns, overwinter distributions, oceanographic characteristics of overwintering grounds, the timing and location of winter moulting, and overlap with anthropogenic impacts. Three dispersal strategies were evident in this population: 1) residents, where birds remained around the UK; 2) short-distance migrants, where birds travelled no further than the Central Atlantic, west of the mid-Atlantic ridge; and 3) long-distance migrants, where individuals reached North America. Long-distance migrants departed the colony on average 19 days earlier than residents, and 9 days earlier than short-distance migrants. Date of departure was not significantly related to distance travelled from the colony, which is a proxy for dispersal strategy. Activity data revealed a potential moulting period of the outer primaries between September and October. The three dispersal strategies overlapped with significantly different levels of anthropogenic impacts, indicating that subsections of the population will be differently affected by human activities. This study provides insight on the variability in nonbreeding dispersal strategies of a relatively unstudied population of kittiwakes, highlighting the drivers of dispersal and factors that may affect them during overwintering.