Foraging segregation between two closely related shearwaters breeding in sympatry

Abstract

Trophic segregation has been proposed as a major mechanism explaining the coexistence of closely related animal taxa. However, how such segregation varies throughout the annual cycle is poorly understood. Here, we examined the feeding ecology of the two subspecies of Cory's shearwater, Calonectris diomedea diomedea and Calonectris diomedea borealis , breeding in sympatry in a Mediterranean colony. To study trophic segregation at different stages, we combined the analysis of isotope values ( δ 15 N, δ 13 C) in blood obtained during incubation and in feathers moulted during chick-rearing and wintering periods with satellite-tracking data during the chick-rearing period. Satellite-tracking and stable isotope data of the first primary feather revealed that C. d. borealis foraged mainly in the Atlantic whereas C. d. diomedea foraged exclusively in the Mediterranean. This spatial segregation could reflect the foraging behaviour of the C. d. borealis individuals before they arrived at the Mediterranean colony. Alternatively, greater wing loading of C. d. borealis individuals may confer the ability to fly across the strong winds occurring at the at the Gibraltar strait. Isotope values of the eighth secondary feather also support segregation in wintering areas between the two forms: C. d. diomedea wintered mainly in association with the Canary current, whereas C. d. borealis wintered in the South African coast. Overall, our results show that spatial segregation in foraging areas can display substantial variation throughout the annual cycle and is probably a major mechanism facilitating coexistence between closely related taxa.

New haematological data in Cory's shearwater,Calonectris diomedea(Aves, Procellariiformes)

“…Indeed, our study was conducted during the pre-laying period whereas that of Forero et al (2006) occurred during incubation (males, of course, do not lay eggs), and haematocrit increases between pre-laying and chick-rearing in female Cory's shearwaters, whereas it remains stable in males . Given that (1) the Cory's shearwaters from the Azores and those studied by Forero et al (2006) and forage in different areas Magalhães et al 2008;Navarro et al 2009), and (2) the haematocrit values we found were higher than those obtained by during the same period of the breeding cycle, the role of geographical origin (i.e. whether environmental conditions might be more stressful at one locality) cannot be dismissed either (Edwards et al 2006).…”

Cool, cold or colder? Spatial segregation of prions and blue petrels is explained by differences in preferred sea surface temperatures

“…Seabird species often breed in large communities and target productive areas within their foraging range, leading to intense competition for resources [1] and reduced foraging efficiency [2]. Seabirds can avoid interspecific competition at least partially by ecological segregation in foraging areas [3,4], diving depths [4,5] or diet choice [6,7]. However, little is known from pelagic birds during the non-breeding season, when seabirds forage over much larger spatial scales.…”

Feather corticosterone of a nestling seabird reveals consequences of sex-specific parental investment

“…First, nestling CORT should be related to variation in duration of foraging trips and foraging efficiency (FE) of parents (i.e. rate of mass gained at sea; see below) because these are measures of parental effort that vary with increasing costs to parents [7,34]. In our population, foraging costs increase with increasing trip length [7] and, at least in other populations, longer trips result in less food being delivered per day to shearwater chicks [35].…”