Animal Movement Studies Research Articles

Muybridge in the Parlor

Commonly regarded as one of the pioneers of motion-picture technology, Eadweard Muybridge carried out several photographic studies of animal and human movement in the late nineteenth century. One of Muybridge's lesser-known commissions was an album of interior photographs that he created in 1880 for his friends Kate and Robert Johnson. This article offers a close reading of this album and argues that it has more in common with Muybridge's motion studies than historians have previously recognized. Far from being a commercial outlier, the album offered Muybridge an opportunity to experiment with the technological and cultural possibilities of photography in a new way. Through ghosts, mirrors, and other forms of representational excess, these images make visible Muybridge's handiwork as a photographer and the intellectual complexity of his collaboration with Kate and Robert Johnson.

Toward a mechanistic understanding of animal migration: incorporating physiological measurements in the study of animal movement.

Movements are a consequence of an individual's motion and navigational capacity, internal state variables and the influence of external environmental conditions. Although substantial advancements have been made in methods of measuring and quantifying variation in motion capacity, navigational capacity and external environmental parameters in recent decades, the role of internal state in animal migration (and in movement in general) is comparatively little studied. Recent studies of animal movement in the wild illustrate how direct physiological measurements can improve our understanding of the mechanisms underlying movement decisions. In this review, we synthesize and provide examples of how recent technical advances in the physiology-related fields of energetics, nutrition, endocrinology, immunology and ecotoxicology provide opportunities for direct measurements of physiological state in the study of animal movement. We then propose a framework for practitioners to enable better integration of studies of physiological state into animal movement ecology by assessing the mechanistic role played by physiology as both a driver and a modulator of movement. Finally, we highlight the current limitations and research priorities for better integration of direct measurements of animal physiological state into the study of animal movement.

AcceleRater: a web application for supervised learning of behavioral modes from acceleration measurements.

BackgroundThe study of animal movement is experiencing rapid progress in recent years, forcefully driven by technological advancement. Biologgers with Acceleration (ACC) recordings are becoming increasingly popular in the fields of animal behavior and movement ecology, for estimating energy expenditure and identifying behavior, with prospects for other potential uses as well. Supervised learning of behavioral modes from acceleration data has shown promising results in many species, and for a diverse range of behaviors. However, broad implementation of this technique in movement ecology research has been limited due to technical difficulties and complicated analysis, deterring many practitioners from applying this approach. This highlights the need to develop a broadly applicable tool for classifying behavior from acceleration data.DescriptionHere we present a free-access python-based web application called AcceleRater, for rapidly training, visualizing and using models for supervised learning of behavioral modes from ACC measurements. We introduce AcceleRater, and illustrate its successful application for classifying vulture behavioral modes from acceleration data obtained from free-ranging vultures. The seven models offered in the AcceleRater application achieved overall accuracy of between 77.68% (Decision Tree) and 84.84% (Artificial Neural Network), with a mean overall accuracy of 81.51% and standard deviation of 3.95%. Notably, variation in performance was larger between behavioral modes than between models.ConclusionsAcceleRater provides the means to identify animal behavior, offering a user-friendly tool for ACC-based behavioral annotation, which will be dynamically upgraded and maintained.Electronic supplementary materialThe online version of this article (doi:10.1186/s40462-014-0027-0) contains supplementary material, which is available to authorized users.

Winter foraging site fidelity of king penguins breeding at the Falkland Islands

Foraging site fidelity has profound consequences for individual fitness, population processes and the effectiveness of species conservation measures. Accordingly, quantifying site fidelity has become increasingly important in animal movement and habitat selection studies. To assess foraging site fidelity in king penguins (Aptenodytes patagonicus) breeding at the Falkland Islands (51.48°S, 57.83°W), we measured overlap in time spent in foraging areas (at a 0.1° × 0.1° grid resolution) between successive foraging trips and foraging route consistency during the creche period. In total, 30 complete foraging trips from seven king penguins were recorded between April and October 2010. King penguins predominantly foraged on the highly productive Patagonian slope, to the north of the Falkland Islands [median foraging trip distance 213 km (SD = 215 km) and duration 12.8 days (SD = 14.7 days)]. Overlap in time spent in an area on consecutive foraging trips ranged between 2 and 73 % (mean 27 %, SD = 22 %). Bearing during the outbound portion of foraging trips was typically highly repeatable for individual birds, but foraging trip duration and distance were not. Travel during the outbound phase of foraging trips was consistent with the direction of the northward-flowing Falkland Current that may act as a directional cue or facilitate rapid transit to foraging areas. Flexibility in foraging trip distances and durations may be a response to changes in resource availability and changes in the energetic requirements of adults and chicks over an extended breeding cycle.

Competition, predation, and migration: individual choice patterns of Serengeti migrants captured by hierarchical models

Large‐herbivore migrations occur across gradients of food quality or food abundance that are generally determined by underlying geographic patterns in rainfall, elevation, or latitude, in turn causing variation in the degree of interspecific competition and the exposure to predators. However, the role of top‐down effects of predation as opposed to the bottom‐up effects of competition for resources in shaping migrations is not well understood. We studied 30 GPS radio‐collared wildebeest and zebra migrating seasonally in the Serengeti‐Mara ecosystem to ask how predation and food availability differentially affect the individual movement patterns of these co‐migrating species. A hierarchical analysis of movement trajectories (directions and distances) in relation to grass biomass, high‐quality food patches, and predation risk show that wildebeest tend to move in response to food quality, with little attention to predation risk. In contrast, individual zebra movements reflect a balance between the risk of predation and the access to high‐quality food of sufficient biomass. Our analysis shows how two migratory species move in response to different attributes of the same landscape. Counterintuitively and in contrast to most other animal movement studies, we find that both species move farther each day when resources are locally abundant than when they are scarce. During the wet season when the quality of grazing is at its peak, both wildebeest and zebra move the greatest distances and do not settle in localized areas to graze for extended periods. We propose that this punctuated movement in high‐quality patches is explained by density dependency, whereby large groups of competing individuals (up to 1.65 million grazers) rapidly deplete the localized grazing opportunities. These findings capture the roles of predation and competition in shaping animal migrations, which are often claimed but rarely measured.

The Correlated Random Walk and the Rise of Movement Ecology

Understanding why, how, and when animals move is essential to many areas of ecology and related fields. Indeed, key aspects of animal behavior, population genetics, biological control, predator–prey dynamics, ecosystem engineering, and conservation biology all hinge upon knowing what critters are moving from where to where in a landscape, including information on how quickly, how regularly, and by what route they travel. The complexities involved in such processes have spawned tremendous efforts in both field research (where goals include measuring and characterizing such movements) and theoretical research (where goals include exploring the nature and potential consequences of movement). Ecologists today routinely receive some training in both empirical and theoretical research, and in the role of statistical analyses and model fitting as a way of linking the two perspectives. However, that has not always been the case. Spatial questions in ecology were long an area where the gulf between theory and reality was particularly wide. In part, this was due to the additional mathematical challenges of spatial models, but it also due to the perhaps greater technological challenges of measuring and contextualizing animal movements.

Change detection in animal movement using discrete wavelet analysis

Animals moving through a complex environment change their movement patterns frequently. Such transitions from one movement behavior to another are a result of multiple factors such as weather, habitat and inter-specific interactions occurring either individually or in tandem. Understanding where and when these changes occur is the first step towards understanding the limiting or key factors acting at different scales.We applied discrete wavelet analysis to find change points in the movement behavior of a Lesser Black-backed gull (Larus fuscus). We compared our results with results from the residence method proposed by Barraquand and Benhamou (2008) and the statistical method proposed by Lavielle (1999, 2005). Discrete wavelet analysis allows the identification and localization of change points by decomposing the frequency content of two time series consisting of step length and residence time data, while omitting the problem of redundancy of coefficients consistent with continuous wavelet transformation of movement data.We show that the novel use of discrete wavelet analysis in animal movement studies is widely applicable on different focus variables, allowing changes in the movement behavior and precise change points to be detected.

Using stable hydrogen isotopes (δ2H) and ring recoveries to trace natal origins in a Eurasian passerine with a migratory divide

Despite recent advances in technology, it remains difficult to connect breeding and non‐breeding areas of populations of migratory organisms due to the challenges of year‐round tracking. Here, we used the Eurasian reed warbler Acrocephalus scirpaceus, a passerine with a pronounced migratory divide to demonstrate the promise of integrating several sources of information within the Bayesian modelling framework for the study of migratory connectivity. To this end, we combined data from stable hydrogen isotope ratios (δ2H) of feathers, ring recoveries, and the geographic delineation of sub‐populations on either side of the migratory divide. Feather δ2H measurements from local juvenile birds sampled across the breeding range tightly correlated with amount‐weighted mean annual precipitation δ2H values predicted for the natal sites. Predicted natal origins of birds intercepted en route in the Mediterranean region largely differed among the five stopover sites. Thanks to the different migratory pathways used by different breeding populations and the existence of a migratory divide, we were able to effectively narrow the assigned regions of origin. Our results show that spatial resolution of likelihood‐based assignments of geographic origins based on δ2H measurements may improve significantly when prior probabilities derived from population‐specific migratory directions are included. Integrating information from stable isotopes, ring recoveries, geolocators and other sources within the Bayesian modelling framework will provide an extremely useful toolbox for the study of animal movements in the future.

Error Properties of Argos Satellite Telemetry Locations Using Least Squares and Kalman Filtering

Study of animal movements is key for understanding their ecology and facilitating their conservation. The Argos satellite system is a valuable tool for tracking species which move long distances, inhabit remote areas, and are otherwise difficult to track with traditional VHF telemetry and are not suitable for GPS systems. Previous research has raised doubts about the magnitude of position errors quoted by the satellite service provider CLS. In addition, no peer-reviewed publications have evaluated the usefulness of the CLS supplied error ellipses nor the accuracy of the new Kalman filtering (KF) processing method. Using transmitters hung from towers and trees in southeastern Peru, we show the Argos error ellipses generally contain <25% of the true locations and therefore do not adequately describe the true location errors. We also find that KF processing does not significantly increase location accuracy. The errors for both LS and KF processing methods were found to be lognormally distributed, which has important repercussions for error calculation, statistical analysis, and data interpretation. In brief, “good” positions (location codes 3, 2, 1, A) are accurate to about 2 km, while 0 and B locations are accurate to about 5–10 km. However, due to the lognormal distribution of the errors, larger outliers are to be expected in all location codes and need to be accounted for in the user’s data processing. We evaluate five different empirical error estimates and find that 68% lognormal error ellipses provided the most useful error estimates. Longitude errors are larger than latitude errors by a factor of 2 to 3, supporting the use of elliptical error ellipses. Numerous studies over the past 15 years have also found fault with the CLS-claimed error estimates yet CLS has failed to correct their misleading information. We hope this will be reversed in the near future.

Plankton 3D tracking: the importance of camera calibration in stereo computer vision systems

Computer vision applications are very useful to study animal movements, but due to their intrinsic complexity they are challenging to design, implement, and use properly. We here describe a calibration procedure for a laboratory stereo vision system for tracking zooplankton in three dimensions (3D). We demonstrate the crucial importance of using a correct calibration for proper interpretation of animal swimming tracks. We also address the effect of the air‐water shift phase in the calibration procedure. Actually, not performing a proper calibration caused an average positional error of more than 25 body‐lengths in the investigated animal Daphnia magna. Furthermore, we evaluate the different outcomes of using 2D and 3D tracks obtained with a calibrated stereo vision system and show that although 2D tracking might be sufficient in some cases, the method was in our study unable to give information of swimming path geometry and underestimated the speed by 25%. Finally, we discuss consequences for biologically relevant questions when an incorrect methodology is used and strongly recommend that future studies provide detailed descriptions of the framework used for calibration to allow for comparisons between different studies.

Ecological and dietary correlates of stable hydrogen isotope ratios in fur and body water of syntopic tropical bats

Hydrogen stable isotope ratios of keratin (delta2H(K)) are increasingly used as endogenous markers to study animal movements, yet it is unclear what factors might influence delta2H(K) in free-ranging animals. We studied hydrogen stable isotope ratios of body water (delta2H(BW)) and fur keratin in 36 bat species (> 400 individuals) from a tropical forest assemblage to evaluate if delta2H(BW) and delta2H(K) are related to body size, trophic position, and movement ecology. We found a relatively large range of delta2H(BW) values (approximately 65 per thousand) across bat species. Our phylogenetically controlled analysis showed that delta2H(BW) was not related to body size, trophic position, or movement ecology of species. The analysis also indicated that delta2H(BW) of primary consumers (i.e., fruit-eating bats) was similar to that of fruit juice, and delta2H(BW) of secondary consumers (i.e., animalivorous bats) was similar to that of surface water. Across bat species, delta2H(K) tended to decrease with increasing delta2H(BW), suggesting that delta2H(K) is not directly linked to delta2H(BW). We further tested whether delta2H(K) varied with a species' trophic position (measured as delta15N) and movement ecology (local or regional species). In syntopic bats, delta2H(K) ranged over 73 per thousand, yet delta2H(K) was related neither to delta15N nor to the movement ecology of species. Fur keratin of secondary consumers was more enriched in 2H by 44 per thousand and in 15N by 3.7 per thousand compared with fur keratin of primary consumers. In an intraspecific analysis, we found that delta2H(K) of an insectivorous bat varied by 20 per thousand between colonies at 4 km distance. Within this species, deltaH(K) was not related to individual delta15N and body mass. Our data suggest that variation in delta2H(K) can be large in bats of tropical assemblages, both across species (range approximately 70 per thousand) and even within sedentary species (range approximately 20 per thousand), and that delta2H(K) is largely affected by the dietary habits of species.

Can brief marking campaigns provide reliable dispersal estimates? A Nickerl’s Fritillary (&lt;i&gt;Melitaea aurelia&lt;/i&gt;, Lepidoptera: Nymphalidae) case study

Functions expressing dispersal probability decays with increasing distance are widely used in studies of animal movements. The inverse power function (IPF) exhibits the property of self-similarity, and hence should perform robustly against variation in marking efforts, allowing comparisons across studies. We investigated this function property using dispersal data of Nickerl’s fritillary (Melitaea aurelia), a little studied checkerspot butterfly which is currently expanding in Central Europe. During mark-recapture in South Moravia, Czech Republic, a single researcher worked for the entire flight period in 2005, while in 2006 five researchers worked for just 5 days. Slopes of the fitted functions did not differ between the two seasons, illustrating the robustness of the function and suggesting the possibility to obtain reliable dispersal estimates even from brief marking campaigns. For both years, it was predicted that approximately one individual per one thousand would cross 10 km distance, the maximum distance separating the most isolated colonies in the region.

Using computational and mechanical models to study animal locomotion.

Recent advances in computational methods have made realistic large-scale simulations of animal locomotion possible. This has resulted in numerous mathematical and computational studies of animal movement through fluids and over substrates with the purpose of better understanding organisms' performance and improving the design of vehicles moving through air and water and on land. This work has also motivated the development of improved numerical methods and modeling techniques for animal locomotion that is characterized by the interactions of fluids, substrates, and structures. Despite the large body of recent work in this area, the application of mathematical and numerical methods to improve our understanding of organisms in the context of their environment and physiology has remained relatively unexplored. Nature has evolved a wide variety of fascinating mechanisms of locomotion that exploit the properties of complex materials and fluids, but only recently are the mathematical, computational, and robotic tools available to rigorously compare the relative advantages and disadvantages of different methods of locomotion in variable environments. Similarly, advances in computational physiology have only recently allowed investigators to explore how changes at the molecular, cellular, and tissue levels might lead to changes in performance at the organismal level. In this article, we highlight recent examples of how computational, mathematical, and experimental tools can be combined to ultimately answer the questions posed in one of the grand challenges in organismal biology: "Integrating living and physical systems."

Estimating animal densities in the aerosphere using weather radar: To Z or not to Z?

Weather radars provide near‐continuous recording and extensive spatial coverage, which is a valuable resource for biologists, who wish to observe and study animal movements in the aerosphere over a wide range of temporal and spatial scales. Powerful biological inferences can be garnered from radar data that have been processed primarily with the intention of understanding meteorology. However, when seeking to answer certain quantitative biological questions, e.g., those related to density of animals, assumptions made in processing radar data for meteorological purposes interfere with biological inference. In particular, values of the radar reflectivity factor (Z) reported by weather radars are not well suited for biological interpretation. The mathematical framework we present here allows researchers to interpret weather radar data originating from biological scatterers (bioscatterers) without relying on assumptions developed specifically for meteorological phenomena. The mathematical principles discussed are used to interpret received echo power as it relates to bioscatterers. We examine the relationships among measurement error and these bioscatter signals using a radar simulator. Our simulation results demonstrate that within 30–90 km from a radar, distances typical for observing aerial vertebrates such as birds and bats, measurement error associated with number densities of animals within the radar sampling volume are low enough to allow reasonable estimates of aerial densities for population monitoring. The framework presented for using radar echoes for quantifying biological populations observed by radar in their aerosphere habitats enhances use of radar remote‐sensing for long‐term population monitoring as well as a host of other ecological applications, such as studies on phenology, movement, and aerial behaviors.

A data efficient method for characterization of chameleon tongue motion using Doppler radar.

A new technique is described for study of the study of high velocity animal movements using a continuous wave Doppler radar operating at 24 GHz. The movement studied was tongue projection kinematics during prey capture by the lizard Chamaeleo Jacksonii. The measurements were verified with a high speed video reference, recorded at 1000 frames per second. The limitations and advantages of both the methodologies are compared and tongue speeds of 3:65 m/s were observed. These results show a useful application of radar to augment visual sensing of biological motion and enable the use of monitoring in a wider range of situations.

Using first-passage time to link behaviour and habitat in foraging paths of a terrestrial predator, the racoon

An understanding of how animals alter their behaviour in relation to environmental conditions is a key element in the study of animal movement, foraging ecology and habitat use, and can provide valuable information for practical conservation and management applications. To exploit resources in heterogeneous landscapes optimally, foragers should intensively search in profitable patches while minimizing foraging activities in low-quality areas. We used first-passage time (FPT) analysis to identify and characterize area-restricted search (ARS) behaviour along the nightly movement paths of racoons. While FPT analysis has been successfully applied to a variety of pelagic species, our goal was to determine the ability of FPT to detect habitat characteristics associated with changes in searching behaviour for a terrestrial predator. Racoons, Procyon lotor , were tracked via radiotelemetry during their nightly movements. We found evidence of ARS behaviour in 55 of 58 paths, with racoons concentrating intensive searching bouts in areas with an average radius of 42.6 m (range 20–100 m). To test whether our detection of ARS represented an actual change in behaviour, we tracked five racoons in relation to an artificial food patch. We detected ARS behaviour during 9 of 10 occasions in which a tracked animal encountered the food patch. Racoons showed ARS behaviour in areas with abundant shallow water, and they moved quickly through openings and dry areas with sparse ground-level vegetation. Application of this method should prove useful for studies of habitat use and foraging ecology of terrestrial predators by providing links between animal movements and the environment.

Factors Influencing the Turnover and Net Isotopic Discrimination of Hydrogen Isotopes in Proteinaceous Tissue: Experimental Results Using Japanese Quail

Stable hydrogen isotopes (δ(2)H) are commonly used in studies of animal movement. Tissue that is metabolically inactive after growth (e.g., feathers) provides spatial or dietary information that reflects only the period of tissue growth, whereas tissues that are metabolically active (e.g., red blood cells) provide a moving window of forensic information. However, using δ(2)H for studies of animal movement relies on the assumption that tissue δ(2)H values reflect dietary δ(2)H values, plus or minus a net diet-tissue discrimination value, and that the turnover rate is known for metabolically active tissue. The metabolic rate of an animal may influence both diet-tissue discrimination values and isotopic tissue turnover rate, but this hypothesis has not been tested experimentally. To examine the metabolic hypothesis, an experimental group of 12 male and 15 female captive Japanese quail (Coturnix japonica) was housed at 8.9°C for 90 d to elevate their metabolic rates (mL CO(2) min(-1)), and a control group of 12 male and 13 female quail was housed at room temperature during the same period. For both experimental and control birds, diet-tissue discrimination values were estimated for red blood cells and feathers. To determine turnover rate, experimental and control birds were switched from a (2)H-enriched diet to a (2)H-depleted diet, with red blood cells sampled before and after diet switch. Metabolic rate did not influence red blood cell hydrogen isotope turnover rate (η(2)(p) = 0.24)) or diet-feather isotope discrimination values (η(2)(p) = 0.86). Diet-feather hydrogen isotopic discrimination had a significant sex plus treatment interaction effect; female feathers were depleted in (2)H relative to food regardless of treatment, whereas male feathers were enriched in (2)H. The effect of sex suggested that experimental studies should examine whether coeval males and females differ in blood δ(2)H levels during certain periods of the annual cycle.

Identifying high residency areas of the threatened St. Lawrence beluga whale from fine-scale movements of individuals and coarse-scale movements of herds

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 450:243-257 (2012) - DOI: https://doi.org/10.3354/meps09570 Identifying high residency areas of the threatened St. Lawrence beluga whale from fine-scale movements of individuals and coarse-scale movements of herds Sébastien Lemieux Lefebvre1,3, Robert Michaud2, Véronique Lesage3,*, Dominique Berteaux4 1Department of Natural Resource Sciences, McGill University, Ste. Anne de Bellevue, Quebec H9X 3V9, Canada 2Group of Research and Education on Marine Mammals, Quebec G1R 1T5, Canada 3Ministry of Fisheries and Oceans, Maurice Lamontagne Institute, Mont-Joli G5H 3Z4, Canada 4Chaire de recherche du Canada en conservation des écosystèmes nordiques et Centre d’Études Nordiques, Université du Québec à Rimouski, Rimouski G5L 3A1, Canada *Corresponding author. Email: veronique.lesage@dfo-mpo.gc.ca ABSTRACT: The development of high-performance tracking and analytical tools has greatly facilitated the study of animal movements, which, in turn, are increasingly employed to study habitat use. However, data on individual movements are rarely available at both broad spatial and temporal scales, limiting their utility for the study of habitat use at population levels. In this study, we propose a novel approach to investigate habitat profitability and population residency patterns by combining the analysis of fine-scale tracking data from individual animals with coarser, short-term movement patterns of herds. We used this approach to identify areas of high residency (AHR) for the St. Lawrence beluga whale Delphinapterus leucas, a population classified as ‘threatened’ under the Canadian Species At Risk Act. We used radio telemetry and a first passage time approach to study the fine-scale daily movements of 30 belugas. Information obtained from these animals on variation of search effort during displacements, scales at which area-restricted search (ARS) occurred, and associated swimming speeds was used to grid our study area and define a criterion for high residency of beluga herds. The beluga herd database used to identify AHR was composed of 772 visual ‘herd follows’ covering a large portion of the beluga population summer distribution. Thirty-three ARS zones were identified at 2 different spatial scales (~500 m and ~1500 m). Using these scales and the swimming speeds associated with ARS to study the residency of herds resulted in the identification of 28 AHRs used by beluga within their summer distribution. KEY WORDS: Residency · Beluga whale · Delphinapterus leucas · Movement · St. Lawrence estuary · First-passage time · Area-restricted search Full text in pdf format PreviousNextCite this article as: Lemieux Lefebvre S, Michaud R, Lesage V, Berteaux D (2012) Identifying high residency areas of the threatened St. Lawrence beluga whale from fine-scale movements of individuals and coarse-scale movements of herds. Mar Ecol Prog Ser 450:243-257. https://doi.org/10.3354/meps09570 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 450. Online publication date: March 29, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Response of butterflies to structural and resource boundaries

1. Two aspects of landscape composition shape the behavioural response of animals to habitat heterogeneity: physical habitat structure and abundance of key resources. In general, within-habitat movement behaviour has been investigated in relation to resources, and preference at boundaries has been quantified in response to physical structure. 2. Habitat preference studies suggest that responses to resources vs. structure should differ, e.g. between male and female animals, and effects of responses to structure and resources may also interact. However, most studies of animal movement combine various aspects of behavioural responses to 'habitat', implicitly assuming that resources and structure are broadly equivalent. 3. We conducted a large-scale experiment of the movement of Fender's blue (Icaricia icarioides fenderi), an endangered butterfly, to investigate butterfly response to physical structure of the landscape (prairie, open woods and dense woods) and to resources [presence or absence of Kincaid's lupine, Lupinus oreganus (larval hostplant patches)]. The experiment included 606 butterfly flight paths across four habitat types and nine ecotones. 4. Responses to physical structure and resource patches were not congruent. Butterflies were attracted to resource patches within both prairies and open woods and moved more slowly when in resource patches. Butterflies tended to prefer prairie at prairie-forest edges but tended to move faster in prairies than in open woods. Physical structure and resources also interacted; butterflies did not respond to physical habitat structure when resource patches spanned prairie - open woods ecotones. 5. Even dense woods were not perfect barriers, in contrast to a large body of literature that assumes insects from open habitats will not enter dense forests. 6. Movement of both males and females responded to resources and structure. However, female butterflies had stronger responses to both resources and structure in most cases. Females had strongest response to resource (hostplant) patches at patch edges, whereas the strongest preference of males was to return to prairie from open forest. 7. If other species behave like Fender's blue, then combining different definitions of 'habitat' (physical structure vs. resources), different aspects of movement (edge preference vs. within-habitat movement) and/or males and females within species could all lead to misleading conclusions. Our results highlight the importance of investigating these responses, and our study provides a framework for separating them in other systems.

The influence of microhabitat, moisture and diet on stable-hydrogen isotope variation in a Neotropical avian food web

Abstract:The application of stable-hydrogen isotope (δD) measurements to the study of animal movement, resource use and physiology depends on understanding factors driving variation in δD in animal tissues. The source of micro-scale variation in δD is poorly known, yet understanding micro-scale patterns of δD could shed light on important ecological processes and improve our abilities to track animal movements. Using linear and additive models, we explored the influence of micro-scale habitat use, moisture and diet on tissue δD values of Nicaraguan cloud-forest birds. Using mist nets, we captured 211 individuals of 22 resident Neotropical species at 500–1390 m asl and collected feather and claw samples. Based on three years of data from year-round sampling, our results suggest that microhabitat, seasonal shifts in moisture δD, and diet all influence bird tissue δD values. Our model results reveal a previously undescribed microgeographical effect on δD, where foraging level (understorey versus overstorey) and foraging location (forest interior versus adjacent coffee plantation) were significant predictors of δD values in bird claws and feathers. Mean claw and feather δD values among species varied from −83‰ to −19‰. Top models for claws and feathers explained 57% and 52% of variation in δD respectively. Direct comparisons of understorey (mean ± SD of −30‰ ± 15‰) versus overstorey (−50‰ ± 15‰) claw values suggest that δD may be useful in tracking vertical, micro-scale movement. Higher δD values in forest understorey birds reveal a heavy reliance upon recycled, fog moisture. Fragmentation and climate change may result in increasingly desiccated cloud forest that may exert a more negative influence on the food webs of understorey species that seem to be supported by recycled sources of moisture in the dry season.