The Effects of Spatially Heterogeneous Prey Distributions on Detection Patterns in Foraging Seabirds

Octavio Miramontes,Frederic Bartumeus,Denis Boyer,Frederick R Adler

doi:10.1371/journal.pone.0034317

Abstract

Many attempts to relate animal foraging patterns to landscape heterogeneity are focused on the analysis of foragers movements. Resource detection patterns in space and time are not commonly studied, yet they are tightly coupled to landscape properties and add relevant information on foraging behavior. By exploring simple foraging models in unpredictable environments we show that the distribution of intervals between detected prey (detection statistics) is mostly determined by the spatial structure of the prey field and essentially distinct from predator displacement statistics. Detections are expected to be Poissonian in uniform random environments for markedly different foraging movements (e.g. Lévy and ballistic). This prediction is supported by data on the time intervals between diving events on short-range foraging seabirds such as the thick-billed murre (Uria lomvia). However, Poissonian detection statistics is not observed in long-range seabirds such as the wandering albatross (Diomedea exulans) due to the fractal nature of the prey field, covering a wide range of spatial scales. For this scenario, models of fractal prey fields induce non-Poissonian patterns of detection in good agreement with two albatross data sets. We find that the specific shape of the distribution of time intervals between prey detection is mainly driven by meso and submeso-scale landscape structures and depends little on the forager strategy or behavioral responses.

Highlights

A number of seabird species search and catch prey in ranges from hundreds to thousands of kilometers away from their nesting sites [1,2,3,4,5,6,7,8]
The distribution {dp(L)=dL has the form l{d 1 exp ({L=ld ), a shape which is not related to that of P0(l): These results illustrate that exponential tails for prey detection statistics are an essential outcome of foraging models, including those generated from Levy processes, when the landscape is Poissonian
Results of the Levy Dust model (LD) and Fractal Local Density (FLD) Models A ballistic walker foraging through a LD with 0:5ƒDF ƒ0:9 produces a flight duration distribution that fits very well the Bird Island [45] and Crozet Islands [10] albatross data over the entire range (Figure 4A-D)

Summary

Introduction

A number of seabird species search and catch prey in ranges from hundreds to thousands of kilometers away from their nesting sites [1,2,3,4,5,6,7,8]. We show that the non-Poissonian albatross data of [10] and [45] can be explained by models of a forager flying over a fractal prey landscape with parameter values consistent with observed resource distributions in the ocean.

Results

Conclusion