Movements of wintering surf scoters: predator responses to different prey landscapes

Abstract

The distribution of predators is widely recognized to be intimately linked to the distribution of their prey. Foraging theory suggests that predators will modify their behaviors, including movements, to optimize net energy intake when faced with variation in prey attributes or abundance. While many studies have documented changes in movement patterns of animals in response to temporal changes in food, very few have contrasted movements of a single predator species naturally occurring in dramatically different prey landscapes. We documented variation in the winter movements, foraging range size, site fidelity, and distribution patterns of a molluscivorous sea duck, the surf scoter (Melanitta perspicillata), in two areas of coastal British Columbia with very different shellfish prey features. Baynes Sound has extensive tidal flats with abundant clams, which are high-quality and temporally stable prey for scoters. Malaspina Inlet is a rocky fjord-like inlet where scoters consume mussels that are superabundant and easily accessible in some patches but are heavily depleted over the course of winter. We used radio telemetry to track surf scoter movements in both areas and found that in the clam habitats of Baynes Sound, surf scoters exhibited limited movement, small winter ranges, strong foraging site fidelity, and very consistent distribution patterns. By contrast, in mussel habitats in the Malaspina Inlet, surf scoters displayed more movement, larger ranges, little fidelity to specific foraging sites, and more variable distribution patterns. We conclude that features associated with the different prey types, particularly the higher depletion rates of mussels, strongly influenced seasonal space use patterns. These findings are consistent with foraging theory and confirm that predator behavior, specifically movements, is environmentally mediated.

Seasonal variation in effects of multiple predators on an intertidal mussel bed: implications for interpretation of manipulative experiments

“…This is consistent with other studies that have suggested that sea ducks can have a great effect on resources (Guillemette et al 1996, Hamilton 2000, Kirk et al 2008). We are confident that ducks were responsible for these effects for a number of reasons.…”

Female breeding dispersal in wolverines, a solitary carnivore with high territorial fidelity

“…This behaviour creates infrequent exceptions to the stable spatial organisation and adds important knowledge regarding the complexity of spacing behaviour in large mammals in general and wolverines in particular. Territorial fidelity is predicted to be low in habitats where food resources are low, variable and unpredictable and deplete fast (Wauters et al 1995;Kirk et al 2008;Edwards et al 2009). This corresponds to the characterization of wolverine habitat in general (Persson 2005;Inman et al 2012b), and particularly in northern Scandinavia where wolverines are highly dependent on migrating reindeer.…”

“…In solitary territorial species, space use is primarily driven by resource competition over access to food or the opposite sex (Sandell 1989;). Territorial fidelity is beneficial because it allows individuals to become familiar with resources in an area, enhancing survival and reproductive success (Switzer 1993;Kirk et al 2008). Furthermore, for species that aggressively defend territories, movement into unfamiliar areas increases mortality risk (Isbell et al 1990;Stamps and Krishnan 2001).…”

Effects of off‐bottom shellfish aquaculture on winter habitat use by molluscivorous sea ducks

“…Kirk et al (2008) found that wintering surf scoter distribution patterns in the Malaspina Complex varied considerably through the season; individual surf scoters displayed extensive movements, had large home ranges, and little fidelity to specific foraging sites. Therefore, in order to capture an overall measure of use of each survey polygon, the cumulative numbers of birds were used as an index and corrected for differences in survey polygon size by expressing the cumulative numbers as densities (number of birds per km 2 ).…”