Passive Interference Competition by Glaucous-Winged Gulls on Black-Legged Kittiwakes: A Cost of Feeding in Flocks

Inter-and intraspecific competition can lead to resource partitioning in sympatric species, processes likely affected by environmental productivity and population size. We investigated the foraging behaviour and diet of masked (Sula dactylatra) and red-footed (S. sula) boobies at Tromelin Island, western Indian Ocean, to examine the role of resource partitioning in the foraging strategies of these sympatric species in an extreme oligotrophic environment. We compared our results to published studies with differing environmental conditions or population sizes. We used GPS loggers and Argos transmitters to track foraging movements and used time-depth recorders to estimate dive depths. Masked boobies travelled further and at faster rates than redfooted boobies, and sexes did not differ in foraging behaviour. Based on randomization tests, the foraging range of each species (95% utilization distribution; UD) overlapped significantly. However, at core foraging areas (50% and 25% UD), interspecific segregation was greater than expected by chance alone. No intraspecific spatial segregation was detected between sexes. Environmental characteristics of area-restricted search zones differed between species, but not sexes; masked boobies utilized warmer, deeper, and less windy oceanic environments than red-footed boobies. Masked boobies attained greater diving depths than red-footed boobies and consumed primarily flying fish, whereas red-footed boobies consumed mostly squid. Red-footed and masked boobies breeding in the extreme oligotrophic environment near Tromelin demonstrated greater dietary partitioning differences in foraging ranges compared to a less oligotrophic environment. This suggests that environmental productivity may play a role in processes of resource partitioning in these sympatric species.KEY WORDS: Resource partitioning · GPS · Satellite tracking · Area-restricted search · Diet · Sula dactylatra · Sula sula Resale or republication not permitted without written consent of the publisher

Section: Introductionmentioning

confidence: 99%

Variability of resource partitioning in sympatric tropical boobies

Kappes¹,

Weimerskirch²,

Pinaud³

et al. 2011

“…Competition for kittiwake is Only provided for species where the functional relationship between group size and population density was saturating Table 3. Fit of the non-linear model between mean crowding on the water and population density for 7 species of seabirds in the Northwest Atlantic in [2006][2007][2008][2009] often caused by the presence of kleptoparasitic gull species (Larus spp) (Maniscalco et al 2001), but this is probably not very frequent here given that mixed-species flocking was relatively rare for kittiwake. Intraspecific competition for food in kittiwake has been suggested as a result of a reduction in prey availability near the surface caused by the presence of conspecifics (Ainley et al 2003), which may explain why kittiwakes do not always join other feeding flocks (Irons 1998).…”

Section: Discussionmentioning

confidence: 99%

Functional relationship between group size and population density in Northwest Atlantic seabirds

Beauchamp¹

2011

In many bird societies, group size results from the fusion and fission of existing groups. Group size dynamics should ideally be investigated in a population-level context since population density is likely to influence the rate of encounter between individuals and thus the value of joining or leaving groups. However, few studies have documented the shape of the functional relationship between group size and population density. The functional relationship can be of 2 types: (1) a strictly increasing function reflecting random joining and leaving, and (2) a saturating function indicating a preference for a range of group sizes so that a large increase in population density results primarily in more groups rather than larger groups. Using at-sea survey data from 2006 to 2010 in the Northwest Atlantic, I documented a saturating functional relationship between group size and population density in 5 species of seabirds and a strictly increasing function in 2 other bird species. The results suggest that upper limits to group sizes may be common in seabirds, perhaps reflecting feeding competition in larger groups.

“…Others have similarly found that the benefits (locating prey) of flock-foraging in gulls (Hoffman et al 1981, Duffy 1983, Götmark et al 1986, Harrison et al 1991, Ostrand 1999 tend to outweigh costs of competition (Maniscalco et al 2001). O'Driscoll et al (1998) similarly found that gulls and shearwaters showed relatively high levels of co-occurrence, while pursuit-divers (shags) did not.…”

Section: Co-occurrence Among and Between Guildsmentioning

confidence: 97%

“…For birds that partake in flocks, the benefits (ability to find prey; aggregation of prey) presumably outweigh any costs of competition (Sealy 1973, Göt-mark et al 1986). However, interference competition has been proposed as a mechanism reducing the likelihood of certain species co-occurring in the same flock (Hoffman et al 1981, Ballance et al 1997, Maniscalco et al 2001, Burger et al 2008.…”

Section: Introductionmentioning

confidence: 99%

Co-occurrence and aggregation of marine birds and mammals in Monterey Bay, California, USA

Henkel¹

2009

Patterns of spatial and temporal co-occurrence or avoidance among different species of marine birds and mammals can provide insights into the degree to which these top predators compete for prey. I conducted at-sea surveys in nearshore waters of Monterey Bay, California, USA, and used a randomization technique to assess co-occurrence patterns of marine birds and mammals in 1 km transect segments. As expected, strongest positive associations were among members of 3 different foraging guilds: pursuit-divers, surface-feeders, and plunge-divers. Within guilds, pursuitdivers exhibited marked avoidance of one another (negative co-occurrence), although surfacefeeders often co-occurred with each other. The study was conducted during 2 yr, 1999 and 2000; during 2000, when predator abundance was greater and prey abundance may have been decreased, pursuit-divers exhibited more avoidance of one another than in 1999. These data suggest that competition reduces foraging ability for pursuit-diving species, making it more profitable for them to disperse more widely, whereas surface-feeding species (primarily gulls) benefit from flock foraging under most conditions. Larger animals tended to frequently co-occur, while the smallest member of each guild tended to avoid other species, indicating competitive exclusion of smaller predators.