Foraging segregation of two congeneric diving seabird species breeding on St. George Island, Bering Sea

Abstract

Abstract. Subarctic environmental changes are expected to affect the foraging ecology of marine top predators, but the response to such changes may vary among species if they use food resources differently. We examined the characteristics of foraging behavior of two sympatric congeneric diving seabird: common (Uria aalge: hereafter COMUs) and thick-billed (U. lomvia: hereafter TBMUs) murres breeding on St. George Island, located in the seasonal sea-ice region of the Bering Sea. We investigated their foraging trip and flight durations, diel patterns of dive depth, and underwater wing strokes, along with wing morphology and blood stable isotope signatures and stress hormones. Accelerationtemperature-depth loggers were attached to chick-guarding birds, and data were obtained from 7 COMUs and 12 TBMUs. Both species showed similar mean trip duration (13.2 h for COMUs and 10.5 h for TBMUs) and similar diurnal patterns of diving (frequent dives to various depths in the daytime and less frequent dives to shallow depths in the nighttime). During the daytime, the dive depths of COMUs had two peaks in shallow (18.1 m) and deep (74.2 m) depths, while those of TBMUs were 20.2 m and 59.7 m. COMUs showed more frequent wing strokes during the bottom phase of dives (1.90 s −1 ) than TBMUs (1.66 s −1 ). Fish occurred more frequently in the bill loads of COMUs (85 %) than those of TBMUs (56 %). The δ 15 N value of blood was significantly higher in COMUs (14.5 ‰) than in TBMUs (13.1 ‰). The relatively small wing area (0.053 m 2 ) of COMUs compared to TBMUs (0.067 m 2 ) may facilitate their increased agility while foraging and allow them to capture more mobile prey such as larger fishes that inhabit deeper depths. These differences in food resource use may lead to the differential responses of the two murre species to marine environmental changes in the Bering Sea.

Niche partitioning of sympatric penguins by leapfrog foraging appears to be resilient to climate change

“…Vertical niche partitioning has been found in a range of diving (Cimino et al., ; Kokubun et al., , ; Mori & Boyd, ) and arboreal (MacArthur, ; Mansor & Ramli, ; Slagsvold, ) species where they occur in sympatry. We found that, while dive depths overlapped considerably, chinstraps dived to significantly deeper depths than Adélies.…”

Peer Review #1 of "Trophic niches of a seabird assemblage in Bass Strait, south-eastern Australia (v0.1)"

“…Seabirds are major consumers of marine biomass, feeding on a variety of fish, cephalopods and crustaceans (Ridoux 1994, Brooke 2004). The foraging niche of seabirds is influenced by a range of factors, including environmental conditions (Waugh & Weimerskirch 2003, Amélineau et al 2016, Jakubas et al 2017, prey availability (Baird 1991, Camprasse et al 2017, morphological characteristics and their influence on flight performance (Phillips et al 2004, Navarro et al 2013, and interspecific competition (González-Solís et al 2008, Phillips et al 2008, Kokubun et al 2016. Competition is thought to promote foraging niche divergence since species occupying the same ecological niche cannot theoretically coexist through time (Schoener 1974).…”

Variability in trophic level and habitat use in response to environmental forcing: isotopic niche dynamics of breeding seabirds in the southeastern Bering Sea

“…Friedlaender et al 2011, Sabarros et al 2012. In seabirds, sympatrically breeding species are known to partition resources horizontally (Cherel et al 2008, Rayner et al 2016, vertically (Navarro et al 2015, Kokubun et al 2016, diurnally (Barger et al 2016), and/or by prey type (Moreno et al 2016, Rayner et al 2016 or size (Mancini & Bugoni 2014). The degree of partitioning can depend upon changes in food availability , or it can occur during energetically taxing life stages such as offspring provisioning (Cherel et al 2008, Barger et al 2016, Delord et al 2016.…”

“…Both murres are pursuit-diving foragers and have access to prey throughout the water column, up to 200 m in depth (Croll et al 1992. Common murres, compared to thick-billed murres, are able to fly greater distances, and the 2 species partition their use of the water column by time of day, distance from the breeding colony, and by foraging depth (Barger et al 2016, Kokubun et al 2016.…”