Resource partitioning between sympatric seabird species increases during chick‐rearing

Abstract

Citation: Barger, C. P., R. C. Young, A. Will, M. Ito, and A. S. Kitaysky. 2016. Resource partitioning between sympatric seabird species increases during chick-rearing. Ecosphere 7(9):e01447. 10. 1002/ecs2.1447 Abstract. Partitioning of resources by competing species of seabirds may increase during periods of food shortages and elevated energy demands. Here, we examined whether food resource partitioning (differential use of foraging habitat or the consumption of different prey species) between common murres (COMU, Uria aalge) and thick-billed murres (TBMU, U. lomvia) breeding on the same colony in the Bering Sea increases with a predictable increase in energy demands between the incubation and chick-rearing stages of reproduction. We assessed the seasonal dynamics of food availability via corticosterone (CORT) levels and examined adult diet (via stable isotope analysis of nitrogen and carbon, SI) and chick diets (based on nest observations). We compared chick provisioning patterns and examined the characteristics of parental foraging habitat via deployment of bird-borne temperature-depth recorders. We found that CORT levels remained low and similar between the species and reproductive stages, reflecting relatively stable and favorable foraging conditions for both murre species during the study period. Comparisons of SI between murres and their potential prey indicated that diets were similar between the species during incubation and diverged during chick-rearing. Chick-rearing common and thick-billed murres also used different foraging habitats, as reflected in travel distances to foraging areas and sea surface temperature distributions of their foraging dives. TBMUs performed shorter foraging trips, deeper dives and delivered squid to their chicks, while COMUs foraged farther from the colony, performed shallower dives, and delivered fish species to their chicks. These results suggest that food resource partitioning between murre species increased during chick-rearing under favorable foraging conditions. Whether the dietary segregation reflected species-specific differences in adults' foraging efficiency, differences in chicks' dietary requirements, or was a way of reducing competition remains unknown. Regardless of the causal mechanism(s), food resource partitioning might ameliorate interspecific competition between sympatrically breeding birds during periods of increased energy demands.

Seasonal and annual differences in the foraging ecology of two gull species breeding in sympatry and their use of fishery discards

“…Furthermore, stable isotopes can be used to investigate niche segregation between species, using the isotopic variation of the animal tissues to calculate their isotopic niche width and overlap (Newsome et al 2007). Overall, stable isotope analysis (SIA) is a powerful tool to unravel niche partitioning among sympatric taxa (Bocher et al 2000, Barger et al 2016, Delord et al 2016, particularly when combined with traditional dietary techniques (Mancini andBugoni 2014, Ronconi et al 2014).…”

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

“…Several studies have pointed out that COMUs use fish almost exclusively, whereas TBMUs use a variety of prey (Hunt Jr. et al, 1981a;Barrett et al, 1997;Bryant et al, 1998;Barger et al, 2016). Whether/how their foraging behavior contributes to these prey differences is, however, not well known.…”

“…TBMUs have also shown intersexual differences in the diel patterns of diving behavior (Jones et al, 2002;Paredes et al, 2008); however, the presence of such habitat partitioning appears to vary by geographical region (Elliott et al, 2010). Between COMUs and TBMUs the overlap in horizontal and vertical foraging habitats and/or in prey species is greater during incubation than chick rearing, possibly to enhance resource partitioning between the species during the energy-demanding chickrearing period (Barger et al, 2016). In this context, a finescale study of murre diving and flight behavior combined with dietary and morphological analyses is needed to better understanding the differences in the ecological niches of these closely related species.…”

“…Whether/how their foraging behavior contributes to these prey differences is, however, not well known. A few studies have revealed inter-or intraspecific differences in the foraging behavior of COMUs and TBMUs from the aspects of morphology and breeding ecology (Barger et al, 2016). Paredes et al (2015) showed that, within TBMU colonies, smaller individuals tended to fly longer distances and dive shallower, whereas the opposite pattern was observed in larger individuals, likely reflecting their body mass and wing loading.…”

“…Both intrinsic and extrinsic factors affect the patterns of segregation. Intrinsic factors include physiology, morphology or energy requirement in relation to breeding stages, and can influence diving depth (Mori and Boyd, 2004), flight distance (Thaxter et al, 2010) or foraging habitat use (Linnebjerg et al, 2013;Barger et al, 2016). Extrinsic factors include oceanographic conditions and prey availability, and may affect the degree of interspecific competition for food resources (Lynnes et al, 2002;Barger and Kitaysky, 2012).…”