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Abstract
For marine top predators like seabirds, the oceans represent a multitude of habitats regarding oceanographic conditions and food availability. Worldwide, these marine habitats are being altered by changes in climate and increased anthropogenic impact. This is causing a growing concern on how seabird populations might adapt to these changes. Understanding how seabird populations respond to fluctuating environmental conditions and to what extent behavioral flexibility can buffer variations in food availability can help predict how seabirds may cope with changes in the marine environment. Such knowledge is important to implement proper long‐term conservation measures intended to protect marine predators. We explored behavioral flexibility in choice of foraging habitat of chick‐rearing black‐legged kittiwakes Rissa tridactyla during multiple years. By comparing foraging behavior of individuals from two colonies with large differences in oceanographic conditions and distances to predictable feeding areas at the Norwegian shelf break, we investigated how foraging decisions are related to intrinsic and extrinsic factors. We found that proximity to the shelf break determined which factors drove the decision to forage there. At the colony near the shelf break, time of departure from the colony and wind speed were most important in driving the choice of habitat. At the colony farther from the shelf break, the decision to forage there was driven by adult body condition. Birds furthermore adjusted foraging behavior metrics according to time of the day, weather conditions, body condition, and the age of the chicks. The study shows that kittiwakes have high degree of flexibility in their behavioral response to a variable marine environment, which might help them buffer changes in prey distribution around the colonies. The flexibility is, however, dependent on the availability of foraging habitats near the colony.
Highlights
Marine habitats worldwide are undergoing rapid changes due to increased anthropogenic impacts, including overfishing, climate change, pollution, and coastal development (Crain, Kroeker, & Halpern, 2008; Game et al., 2009; Halpern et al, 2008)
There was a fivefold difference in distance to the feeding area at the shelf break between the two study colonies
The average path lengths were twice and eight times as long, for Anda and Sør-Gjæslingan, respectively, when birds went to forage at the shelf break compared to coastal habitats
Summary
Marine habitats worldwide are undergoing rapid changes due to increased anthropogenic impacts, including overfishing, climate change, pollution, and coastal development (Crain, Kroeker, & Halpern, 2008; Game et al., 2009; Halpern et al, 2008). Kittiwakes are sensitive to variations in food availability because they, as surface feeders, FIGURE 1 Breeding black-legged kittiwake (Rissa tridactyla) with two chicks at the colony on Anda rely on crustaceans or fish being available near the surface (Monaghan, 1996) They have limited capacities to switch to alternative prey (Furness & Tasker, 2000; Piatt et al, 2007), and to buffer environmental variability (Monaghan, 1996). The waters off the coast of Norway are highly productive due to favorable oceanographic conditions linked to the two north-flowing currents, the Norwegian Coastal Current close to shore and the North Atlantic Current, which transport warm saline water along the continental shelf (Barrett, Lorentsen, & Anker-Nilssen, 2006; Skjoldal, Dalpadado, & Dommasnes, 2004) This creates a productive frontal zone (the coastal front) following the edge of the continental shelf (Rey, 2004), with predictable food prey availability to seabirds. Our central research questions were as follows: (1) Which extrinsic and intrinsic factors affect the choice of foraging habitat? (2) How do between-colony differences in proximity to foraging habitats affect foraging decisions?, and (3) How is kittiwake behavior during foraging trips influenced by extrinsic and intrinsic factors in the respective foraging habitats?
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