Coupling instantaneous energy-budget models and behavioural mode analysis to estimate optimal foraging strategy: an example with wandering albatrosses

Abstract

BackgroundHow foragers move across the landscape to search for resources and obtain energy is a central issue in ecology. Direct energetic quantification of animal movements allows for testing optimal foraging theory predictions which assumes that animals forage so as to maximise net energy gain. Thanks to biologging advances, we coupled instantaneous energy-budget models and behavioural mode analysis to test optimal foraging theory predictions on wandering albatross Diomedea exulans during the brooding period. Specifically, the instantaneous energy-budget model considered the energetic balance (i.e., the difference between empirical energy gain data and modelled energy expenditure via heart rate values) along the trajectory of a given individual. Four stereotypic instantaneous behavioural modes were identified based on trajectory properties (e.g., speed and turning angle) by applying a new algorithm called Expectation Maximization Binary Clustering. Previous studies on this species have shown that foraging-in-flight is the optimal foraging strategy during the incubation period when albatrosses undertake long-distance movements but no specific foraging strategy has been determined for shorter foraging movements (e.g., brooding period).ResultsThe output of our energy-budget model (measured as net energy gain) highlighted the potential optimality of alternative search strategies (e.g., sit-and-wait) during brooding, when birds may be subjected to specific energetic trade-offs and have to adapt their foraging strategies accordingly. However, not all birds showed this pattern, revealing the importance of considering individual variability in foraging strategies, as well as any switching among strategies, before drawing population-level generalizations. Finally, our study unveils the importance of considering fine scale activities to make realistic estimates of trip energy expenditure for flying birds at sea.ConclusionsThe up-scaling of accurately measured fine-scale energy patterns is essential to quantify energy balances, and their fluctuations by season of different activities among individuals or populations. In particular, we offer new insights for the energetic quantification of the effect of changing oceanic winds on the biology of pelagic predators in the southern oceans.Electronic supplementary materialThe online version of this article (doi:10.1186/2051-3933-2-8) contains supplementary material, which is available to authorized users.

Early‐life foraging: Behavioral responses of newly fledged albatrosses to environmental conditions

“…However, they can also feed successfully at night (Weimerskirch, Gault, et al., ; Weimerskirch et al., ), through the use of a “sit‐and‐wait” foraging strategy (which is likely included in our active‐sitting behavior), has been suggested as an efficient alternative to the forage‐in‐flight strategy, particularly when individuals are highly time constrained (e.g., breeding adults; Louzao et al. ()). During such periods, it may be difficult for birds to satisfy energetic demands during daylight hours, and so compensatory night foraging may be required.…”

“…When over waters deeper than 3,000 m (i.e., the majority of south western Indian Ocean), individuals were more likely to perform larger scale movements by performing ballistic movements. In contrast, diffusive movements were favored when flying over waters shallower than 3,000 m. Such sinuous movements are typically related to area restricted search behaviors (Kareiva & Odell, ; Louzao et al., ), which generally occur in areas of higher and more predictable prey density (Weimerskirch et al., ). The increased use of these types of strategies by juveniles in shallower waters may reflect the increased presence of favorable foraging habitats such as shelf slopes, seamounts, and ridges, which can aggregate prey (Fauchald & Tveraa, ; Louzao et al., ; Paiva, Geraldes, Ramírez, Garthe, & Ramos, ), which would trigger more intense exploration and/or use of prey search behaviors.…”

Search and foraging behaviors from movement data: A comparison of methods

“…EMbC is a relatively modern technique that is gaining traction within movement ecology. It has previously been used in a variety of movement studies, including exploring behavioral differences between distinct populations of the red‐footed booby (Mendez et al., ) and coupling energy budgets with behavioral patterns under an optimal foraging framework (Louzao, Wiegand, Bartumeus, & Weimerskirch, ). Analysis was undertaken using the EMbC package in R (Garriga & Bartumeus, ), using calculated velocities and turning angles to infer behavioral classifications.…”

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

“…Each location was clustered by the algorithm into 4 behaviour categories (Table 2): High velocity/Low turn (HL), High velocity/High turn (HH), Low velo city/Low turn (LL), Low velocity/High turn (LH). A behavioural mode was assigned to each cluster, as suggested by Louzao et al (2014). The HL and HH labels correspond respectively to travelling and re locating.…”