Foraging distribution of a tropical seabird supports Ashmole’s hypothesis of population regulation

While interspecific differences in foraging behaviour have attracted much attention, less is known about how foraging behaviour differs between populations of the same species.Here we compared the foraging strategy of a pantropical seabird, the red-footed booby Sula sula, in 5 populations breeding in contrasted environmental conditions. The foraging strategy strongly differed between sites, from strictly diurnal short trips in Europa Island (Mozambique channel) to long trips including up to 5 nights at sea in Genovesa Island (Galapagos archipelago). The Expectation Maximisation binary Clustering (EMbC) algorithm was used to determine the different behaviours of individuals during their foraging trips (travelling, intensive foraging, resting and relocating). During the day, the activity budget was similar for all the breeding colonies. During the night, birds were primarily on the water, drifting with currents. At all sites, birds similarly performed intensive foraging in zones of area-restricted search (ARS), although the size and duration of ARS zones differed markedly. Red-footed boobies foraged over deep oceanic waters, with chlorophyll a concentrations varying between sites. Birds did not appear to target areas with higher productivity. We suggest that range differences between populations may be linked to other factors such as intra-and interspecific competition.

Section: Resource Partitioningsupporting

confidence: 74%

“…Kappes et al 2011, Oppel et al 2015. The wide distribution of RFB populations provides the opportunity to examine the influence of contrasted biotic and abiotic conditions from different breeding sites on foraging behaviour.…”

Section: Introductionmentioning

confidence: 99%

Geographical variation in the foraging behaviour of the pantropical red-footed booby

Mendez¹,

Borsa²,

Cruz³

et al. 2017

“…Tropical seabirds frequently exploit all marine areas within a species' flight range, leading to a dispersed distribution around islands (Kappes et al 2011, Hennicke & Weimerskirch 2014, Oppel et al 2015. This dispersed distribution could occur by individuals consistently travelling to a certain location, with individuals exhibiting differences in their preferred foraging location, thus leading to a dispersed distribution at the population level.…”

Section: Introductionmentioning

confidence: 99%

Seasonal shifts in foraging distribution due to individual flexibility in a tropical pelagic forager, the Ascension frigatebird

Oppel¹,

Weber²,

Weber³

et al. 2017

Predators exploiting tropical pelagic waters characterised by low fluctuations in seasonal temperature and salinity may require different foraging strategies than predators that can rely on persistently productive marine features. Consistent individual differences in foraging strategies have been found in temperate seabirds, but it is unclear whether such foraging specialisation would be beneficial in unpredictable tropical pelagic waters. We examined whether foraging trip characteristics of a tropical seabird were consistent between seasons and within individuals and explored whether seasonal changes could be explained by environmental variables. Ascension frigatebird Fregata aquila trips lasted up to 18 d and covered a total travel distance of up to 7047 km, but adult frigatebirds stayed within a radius of 1150 km of Ascension Island. We found that the 50% utilisation distribution of the population expanded southwestward in the cool season due to individuals performing more and longer trips in a southerly and westerly direction during the cool compared to the hot season. Individual repeatability was low (R < 0.25) for all trip characteristics, and we were unable to explain seasonal changes in time spent at sea using oceanographic or atmospheric variables. Instead, frigatebird usage per area was almost exclusively determined by distance from the colony, and although individuals spent more time in distant portions of their foraging trips, the amount of time spent per unit area decreased exponentially with increasing distance from the colony. This study indicates that, in a relatively featureless environment, high individual consistency may not be a beneficial trait for pelagic predators.

“…Phillips et al 2005, Dias et al 2013, Ceia et al 2014, Yamamoto et al 2014, Potier et al 2015. The most common summary data derived from each trip that have been used in this way include the total duration, total distance travelled (summed great circle distances between fixes), maximum range (great circle distance to the furthest location), and bearing at departure or to the furthest point (Hamer et al 2001, 2007, Soanes et al 2013, Ceia et al 2014, Patrick et al 2014, Baylis et al 2015b, Oppel et al 2015, Potier et al 2015. For the non-breeding season, the analyses are often of migration schedules (timing and duration of events; Croxall et al 2005, Dias et al 2011, Yamamoto et al 2014, or the total distance travelled during the migration (Muller et al 2014).…”

Section: Analyses Of Trip Summary Statisticsmentioning

confidence: 99%

“…For Gaussian data, such as ratios of carbon and nitrogen, repeatabilities can be calculated either with the F table of an ANOVA with individual identities as fixed factors (e.g. Hamer et al 2001, Gray et al 2005, Vander Zanden et al 2013, Oppel et al 2015 or with linear mixed-effects models with individual identities treated as a random effect (e.g. Dias et al 2011, Matich et al 2011, Grist et al 2014, McFarlane Tranquilla et al 2014, Kernaléguen et al 2015, Wake field et al 2015.…”

Section: Diet (Trophic Position/carbon Source) Using Stable Isotopesmentioning

confidence: 99%

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

Carneiro¹,

Bonnet‐Lebrun²,

Manica³

et al. 2017

There is increasing realisation that individuals in many animal populations differ substantially in resource, space or habitat use. Differences that cannot be attributed to any a priori way of classifying individuals (i.e. age, sex and other group effects) are often termed 'individual specialisation'. The aim of this paper is to assess the most common approaches for detecting and quantifying individual specialisation and consistencies in foraging behaviour, movement patterns and diet of marine predators using 3 types of data: conventional diet data, stable isotope ratios and tracking data. Methods using conventional diet data rely on a comparison between the proportions of each dietary source in the total diet and in the diet of individuals, or analyses of the statistical distribution of a prey metric (e.g. size); the latter often involves comparing ratios of individual and population variance. Approaches frequently used to analyse stable isotope or tracking data reduced to 1 dimension (trip characteristics, e.g. maximum trip distance or latitude/longitude at certain landmarks) include correlation tests and repeatability analysis. Finally, various spatial analyses are applied to other types of tracking data (e.g. distances between centroids of distributions or migratory routes, or overlap between distributions), and methods exist to compare habitat use. We discuss the advantages and disadvantages of these approaches, issues arising from other effects unrelated to individual specialisation per se (in particular those related to temporal scale) and potential solutions.