Foraging Responses of Black-Legged Kittiwakes to Prolonged Food-Shortages around Colonies on the Bering Sea Shelf

Abstract

We hypothesized that changes in southeastern Bering Sea foraging conditions for black-legged kittiwakes (Rissa tridactyla) have caused shifts in habitat use with direct implications for population trends. To test this, we compared at-sea distribution, breeding performance, and nutritional stress of kittiwakes in three years (2008–2010) at two sites in the Pribilof Islands, where the population has either declined (St. Paul) or remained stable (St. George). Foraging conditions were assessed from changes in (1) bird diets, (2) the biomass and distribution of juvenile pollock (Theragra chalcogramma) in 2008 and 2009, and (3) eddy kinetic energy (EKE; considered to be a proxy for oceanic prey availability). In years when biomass of juvenile pollock was low and patchily distributed in shelf regions, kittiwake diets included little or no neritic prey and a much higher occurrence of oceanic prey (e.g. myctophids). Birds from both islands foraged on the nearby shelves, or made substantially longer-distance trips overnight to the basin. Here, feeding was more nocturnal and crepuscular than on the shelf, and often occurred near anticyclonic, or inside cyclonic eddies. As expected from colony location, birds from St. Paul used neritic waters more frequently, whereas birds from St. George typically foraged in oceanic waters. Despite these distinctive foraging patterns, there were no significant differences between colonies in chick feeding rates or fledging success. High EKE in 2010 coincided with a 63% increase in use of the basin by birds from St. Paul compared with 2008 when EKE was low. Nonetheless, adult nutritional stress, which was relatively high across years at both colonies, peaked in birds from St. Paul in 2010. Diminishing food resources in nearby shelf habitats may have contributed to kittiwake population declines at St Paul, possibly driven by increased adult mortality or breeding desertion due to high foraging effort and nutritional stress.

Circumpolar dynamics of a marine top‐predator track ocean warming rates

“…Peak hatching occurs in June–July depending on the colony and is usually later at higher latitudes (Burr et al., ). Kittiwakes breed on coastal cliffs in single‐ or mixed‐species colonies ranging in size from tens to tens of thousands of breeding pairs and forage in coastal and pelagic habitats up to several hundred kilometers from the colony (Goutte et al., ; Irons, ; Paredes et al., ). Their diet consists predominantly of fish and marine invertebrates located in the upper 1–2 m of the water column (Coulson, ).…”

“…We calculated the spring sea‐surface temperature or SST (average of mean SST in May and June) in 2° × 2° latitude/longitude cells adjacent to each colony (Figure ). Such large areas should encompass most of the kittiwake foraging grounds in spring and summer (Daunt et al., ; Goutte et al., ; Paredes et al., for some examples of tracking studies describing the foraging range of kittiwakes in different parts of its breeding range). Data on reconstructed SST were obtained from the climate data library from the International Research Institute for Climate and Society http://iridl.ldeo.columbia.edu/SOURCES/.NOAA/.NCDC/.ERSST/.version3b/.sst/ (Smith, Reynolds, Peterson, & Lawrimore, ; Xue, Smith, & Reynolds, ).…”

“…| 3771 coastal and pelagic habitats up to several hundred kilometers from the colony (Goutte et al, 2014;Irons, 1998;Paredes et al, 2014).…”

Survival estimates strongly depend on capture–recapture designs in a disturbed environment inducing dispersal

“…This means that even if individuals have dispersed out of the monitored area, they may occasionally come back to prospect, notably if they have failed their breeding attempt. This might induce temporal heterogeneity in detection probabilities intra-seasonally (Chambert et al 2012), but also interannually, as kittiwake breeding success can be highly variable in time and space (Paredes et al 2014, Ponchon et al 2014. Therefore, in the current case study, heterogeneity in detection probabilities may mostly originate from a strong temporary emigration (Table 4, 5), but also from individual site fidelity conditioned by individual and conspecific breeding performance involving a memory effect.…”

Food supplementation by an invasive fleshy‐fruited shrub sustains body condition of a native frugivorous bird during winter

“…Animals tend to adjust their behavior and physiology to changes in food availability in their environment (Gleditsch & Carlo 2011;Sofaer et al 2013;Paredes et al 2014). In seasonal environments, fluctuation of food resources is the norm (i.e.…”