Individual differences in foraging site fidelity are not related to time-activity budgets in Herring Gulls

Many populations consist of individuals that differ consistently in their foraging behaviour through resource or foraging site selection. Foraging site fidelity has been reported in several seabird species as a common phenomenon. It is considered especially beneficial in spatially and/or temporally predictable environments in which fidelity is thought to increase energy intake, thereby affecting time-energy budgets. However, the consequences for activity and energy budget have not been adequately tested. In this paper, we studied the consequences of fine-scale foraging site fidelity in adult Herring Gulls Larus argentatus in a highly predictable foraging environment with distinct foraging patches. We measured their time-activity budgets using GPS tracking and tri-axial acceleration measurements, which also made it possible to estimate energy expenditure. Individual variation in foraging site fidelity was high, some individuals spending most of their time on a single foraging patch and others spending the same amount of time in up to 21 patches. While time and activity budgets differed between individuals, we found no clear relationship with foraging site fidelity. We did find a relationship between the size of the birds and the level of site fidelity; faithful birds tend to have a larger body size. Although differences in foraging time and habitat use between individuals could play a role in the results of the current study, short-term consequences of variation in foraging site fidelity within a population remain elusive, even when focusing on individuals with a similar foraging specialization (Blue Mussels Mytilus edulis). Studying individuals over multiple years and under varying environmental conditions may provide better insight into the consequences and plasticity of foraging site fidelity.     

Intrinsic and extrinsic drivers of activity budgets in sympatric grey and harbour seals

Investigation of activity budgets in relation to seasonal, intrinsic (age, sex) and extrinsic (time of day, spatial) covariates enables an understanding of how such covariates shape behavioural strategies. However, conducting such investigations in the wild is challenging, because of the required large sample size of individuals across the annual cycle, and difficulties in categorising behavioural states and analysing the resulting individual‐referenced and serially correlated data. In this study, from telemetry tags deployed on 63 grey seals Halichoerus grypus and 126 harbour seals Phoca vitulina we used behavioural data, and movement data within a Bayesian state–space model (SSM), to define population‐level activity budgets around Britain. Using generalised estimating equations (GEEs) we then examined how time spent in four states (resting on land (hauled out), resting at sea, foraging and travelling) was influenced by seasonal, intrinsic and extrinsic covariates. We present and discuss the following key findings. 1) We found no evidence that regional variation in foraging effort was linked to regional population trajectories in harbour seals. 2) Grey seals demonstrated sex‐specific seasonal differences in their activity budgets, independent from those related to reproductive costs. 3) In these sympatric species there was evidence of temporal separation in time hauled out, but not in time foraging. 4) In both species, time spent resting at sea was separated into inshore (associated with tidal haul out availability) and offshore areas. Time spent resting at sea and on land was interchangeable to some extent, suggesting a degree of overlap in their functionality. This may result in a relaxation of the constraints associated with a central place foraging strategy. More generally, we demonstrate how a large dataset, incorporating differing tag parameters, can be analysed to define activity budgets and subsequently address important ecological questions.     

Temporal effects of disturbance on community composition in simulated stage‐structured plant communities

In an era of global environmental change, understanding how disturbance affects the dynamics of ecological communities is crucial. However, few studies have theoretically explored the potential influence of disturbance including both intensity and frequency on compositional change over time in communities with stage structure. A spatially explicit, individual‐based model was constructed incorporating the various demographic responses to disturbance of plants at two different growth stages: seedlings and adults. In the model, we assumed that individuals within each stage were demographically equivalent (neutral) but differed between stages. We simulated a common phenomenon that seedlings suffered more from disturbance such as grazing and fire than adults. We showed how stage‐structured communities of seedlings and adults responded to disturbance with various levels of disturbance frequency and intensity. In “undisturbed” simulations, the relationship between average species abundance (defined here as the total number of individuals divided by species richness) and community composition turnover (measured by the Bray–Curtis similarity index) was asymptotic. However, in strongly “disturbed” simulations with the between‐disturbance intervals greater than one, this relationship became unimodal. Stage‐dependent response to disturbance underlay the above discrepancy between undisturbed and disturbed communities.     

The consequences of size dependent foraging for food web topology

A general question in biology is how processes at one scale, for example that of individual organisms, influence patterns at larger scales, for example communities of interacting individuals. Here we ask how changing the size‐dependence of the foraging behaviour of individuals can influence the structure of food webs. We assembled communities using a model in which species interactions are determined by allometric foraging rules of (1) handling time and (2) attack rates, and also (3) the distribution of body sizes. We systematically varied these three factors and examined their effects on three community level, food web allometries: the generality ‐ mass correlation, the vulnerability ‐ mass correlation and the trophic height ‐ mass correlation. The results demonstrate how allometries of individual foraging behaviour (handling time and attack rates) are linked across scales of organisation: different community level allometries are influenced by different individual level allometries. For example, generality allometries in the community are most affected by the individual allometric relationships of the attack rate, whereas trophic level allometries in the community are more strongly influenced by variation in individual handling time allometries. Importantly, we also find that the shape of the body size distribution from which species are drawn has a substantial influence on how these links between scales operate. This study suggests that understanding the variation of size structure among ecological networks requires knowledge about the causes of variation in individual foraging behaviour and determinants of the regional body size distribution.     

Forest Modification Affects Diversity (But Not Dynamics) of Speciose Tropical Pyraloid Moth Communities

We studied temporal and spatial dynamics of extremely diverse moth ensembles (Lepidoptera: Pyraloidea) along a gradient of forest disturbance ranging from undisturbed primary tropical rain forest to different kinds of modified forest and open cultivated land at the margin of Mount Kinabalu National Park (Sabah, East Malaysia). We sampled moths by light trapping during two periods (March‐May and August‐September 1997). We collected a total of 7724 individuals representing 680 species during 78 light‐trapping nights at six study sites. Species diversity (Fisher's α) of ensembles in undisturbed primary forest was distinctly higher than in disturbed or secondary forest. More pyraloid moths were attracted in undisturbed primary forest. Samples from disturbed primary or old‐growth secondary forest were statistically indistinguishable from the undisturbed primary forest ensemble in regard to species composition. Thus, pyraloid ensembles from disturbed forest with tall trees remaining appeared to represent impoverished subsets of the undisturbed primary forest community. The more heavily disturbed sites had a distinct fauna and showed a stronger faunal differentiation among each other. Four species of the genus Eoophyla, in which aquatic larvae feed on algae in fast‐running streams benefited prominently from forest disturbance. Temporal variation of ensembles was remarkably concordant across the disturbance gradient. Relative abundance variation of the commonest species was identical at all sites. Overall, pyraloid moths responded more sensitively to anthropogenic habitat alteration than most other moth taxa studied thus far in tropical regions and allowed for an analysis of diversity patterns at a high temporal resolution.     

Human Activity Dampens the Benefits of Group Size on Vigilance in Khulan (Equus hemionus) in Western China

Animals receive anti-predator benefits from social behavior. As part of a group, individuals spend less time being vigilant, and vigilance decreases with increasing group size. This phenomenon, called “the many-eyes effect”, together with the “encounter dilution effect”, is considered among the most important factors determining individual vigilance behavior. However, in addition to group size, other social and environmental factors also influence the degree of vigilance, including disturbance from human activities. In our study, we examined vigilance behavior of Khulans (Equus hemionus) in the Xinjiang Province in western China to test whether and how human disturbance and group size affect vigilance. According to our results, Khulan showed a negative correlation between group size and the percentage time spent vigilant, although this negative correlation depended on the groups’ disturbance level. Khulan in the more disturbed area had a dampened benefit from increases in group size, compared to those in the undisturbed core areas. Provision of continuous areas of high-quality habitat for Khulans will allow them to form larger undisturbed aggregations and to gain foraging benefits through reduced individual vigilance, as well as anti-predator benefits through increased probability of predator detection.     

Nutrient release from moose bioturbation in aquatic ecosystems

While the ecological importance of bioturbation is well recognized and the prevalence of aquatic foraging by terrestrial ungulates is increasingly appreciated, research linking how terrestrial ungulates function as disturbance mechanisms via bioturbation in freshwater systems is lacking. The purpose of this study was to quantify potential nutrient pulses released from benthic sediments into the water column when moose Alces alces feed on aquatic plants. We also determined if we could experimentally mimic the benthic disturbance and the expected nutrient pulse created when moose feed aquatically. When moose foraged aquatically, significant releases of both total and dissolved phosphorus (P) and nitrogen (N) resulted in the waters that were disturbed in foraging areas compared to adjacent undisturbed waters. Nutrient concentrations for total P and N ranged from 42.5 × and 2.7 × greater in disturbed than undisturbed, respectively. Dissolved P and N were 26.8 × and 1.5 × greater, respectively, in disturbed versus undisturbed waters. Our experimental mimic created increases of total and dissolved P and N that were equivalent to pulses created by moose. This indicates that it is possible to experimentally test by proxy the potential impact of moose bioturbation on other ecosystem processes. This study is the first quantification of moose foraging as a consumer mechanism that influences the release of limiting nutrients in aquatic systems, thereby emphasizing the potential cascading importance for nutrient uptake and productivity of plants and microbes.     

Individual foraging specialisation in a social mammal: the European badger (Meles meles)

Individual specialisation has been identified in an increasing number of animal species and populations. However, in some groups, such as terrestrial mammals, it is difficult to disentangle individual niche variation from spatial variation in resource availability. In the present study, we investigate individual variation in the foraging niche of the European badger (Meles meles), a social carnivore that lives in a shared group territory, but forages predominantly alone. Using stable isotope analysis, we distinguish the extent to which foraging variation in badgers is determined by social and spatial constraints and by individual differences within groups. We found a tendency for individual badgers within groups to differ markedly and consistently in their isotope values, suggesting that individuals living with access to the same resources occupied distinctive foraging niches. Although sex had a significant effect on isotope values, substantial variation within groups occurred independently of age and sex. Individual differences were consistent over a period of several months and in some instances were highly consistent across the two years of the study, suggesting long-term individual foraging specialisations. Individual specialisation in foraging may, therefore, persist in populations of territorial species not solely as a result of spatial variation in resources, but also arising from individuals selecting differently from the same available resources. Although the exact cause of this behaviour is unknown, we suggest that specialisation may occur due to learning trade-offs which may limit individual niche widths. However, ecological factors at the group level, such as competition, may also influence the degree of specialisation.     

The cost of disturbance: a waste of time and energy?

Quantifying the effect of disturbance is a central issue in conservation. Using time and energy budgets, we obtain a range of ways to assess the importance of disturbance. One measure is the time that must be spent foraging in order to balance the energy budget. From this we derive critical levels of wastage (rate of disturbance multiplied by duration of disturbance) at which the animal runs out of time or reaches a limit on energy expenditure. In the case of the time constraint, the critical wastage is the net rate of energetic gain while foraging divided by the rate of energetic expenditure during a disturbance. The associated critical rate of disturbance is the net rate of energetic gain while foraging divided by the energy spent during a disturbance. The model is illustrated using data from the African wild dog, which suffers disturbance from lions and kleptoparasitism from hyenas. Findings suggest that disturbance imposes significant costs on wild dog time and energy budgets. We show how alternative environments can be evaluated in terms of their effective rate of gain, which is the net rate of gain from foraging minus the rate of energy expenditure as a result of disturbance.     

Behavioral plasticity and consistency in the naked-footed mouse (<Emphasis Type="Italic">Peromyscus nudipes</Emphasis>) with habitat disturbance

Very few studies have evaluated whether habitat disturbance affects behavioral consistency and plasticity. We measured shyness–boldness and exploration–avoidance for the first time in naked-footed mice (Peromyscus nudipes) in two adjacent habitats with differing level of disturbance in Costa Rica. Each habitat was measured in different, consecutive years. With these data, we explored the possibility of habitat differences in individual- and population-level behavioral plasticity, magnitude of behavior, and consistency. Mice in both habitats behaved consistently across time with high repeatability (i.e., showed personality). The strength of consistency of shyness–boldness and exploration–avoidance over time was higher in the disturbed habitat, and individuals in the undisturbed habitat were bolder and less exploratory. Behaviors were correlated with each other in both habitats, indicating that behavioral syndromes do not always break down in disturbed areas. Mice changed the magnitude of their response the second time they were tested, indicating population-level plasticity. There was also greater individual plasticity among mice in the undisturbed habitat. Our study suggests the possibility that habitat disturbance can affect behavioral plasticity and personality and that shyer/more exploratory individuals might colonize and/or persist in disturbed habitats. These results are preliminary and exploratory because we did not control for temporal differences between habitats.     

Variation in harbour porpoise activity in response to seismic survey noise

Animals exposed to anthropogenic disturbance make trade-offs between perceived risk and the cost of leaving disturbed areas. Impact assessments tend to focus on overt behavioural responses leading to displacement, but trade-offs may also impact individual energy budgets through reduced foraging performance. Previous studies found no evidence for broad-scale displacement of harbour porpoises exposed to impulse noise from a 10 day two-dimensional seismic survey. Here, we used an array of passive acoustic loggers coupled with calibrated noise measurements to test whether the seismic survey influenced the activity patterns of porpoises remaining in the area. We showed that the probability of recording a buzz declined by 15% in the ensonified area and was positively related to distance from the source vessel. We also estimated received levels at the hydrophones and characterized the noise response curve. Our results demonstrate how environmental impact assessments can be developed to assess more subtle effects of noise disturbance on activity patterns and foraging efficiency.     

Impacts of disturbance on migratory waterfowl

It is well known that disturbance from human activities can cause temporary changes in behaviour and locally affect temporal and spatial distribution of migratory and wintering waterfowl. But it is also known that, to some extent, birds can compensate for disturbance by altering their behaviour or habituating to human activities. Comparatively little is known about how these reactions to disturbance may impact on the large-scale dispersion of waterfowl and, ultimately, on their population dynamics. To be able to answer these questions, a better theoretical framework, based on optimal foraging theory incorporating predation risk, and field experiments are required. Furthermore, we need to study the waterfowl throughout their winter ranges to interpret the overall impacts of disturbance. This paper examines two cases where the impacts of disturbance have been assessed from field experiments. In one study, disturbance effects of shooting were tested by setting up experimental reserves in two Danish coastal wetlands. Over a 5-year period, these became two of the most important staging areas for coastal waterfowl, and the national totals of key species were significantly increased. A national management plan which will establish more than 50 new shooting-free refuges on Danish coastal areas within the next 5 years is likely to boost waterfowl numbers even more. Such retention of birds at more northerly sites on the fiyway should result in a more efficient resource utilization and may positively affect the population dynamics where numbers are affected by winter resources. In a second study, the impacts of disturbance by farmers on spring fattening of Pink-footed Geese Anser brachyrhynchus were analysed. In undisturbed areas in northern Norway, abdominal profiles of the geese increased rapidly, whereas in disturbed sites they did not. Subsequently, geese that had used undisturbed sites reproduced better than geese from disturbed sites.     

Effects of small-scale habitat disturbance on the ecology of breeding birds in a Vermont (USA) hardwood forest

We studied territory placement and foraging behavior of breeding birds in relation to juxtaposition of forest vegetation and logged patches in southern Vermont, USA Different bird species used disturbed vegetation at differing spatial scales, depending on temtory size Four species Dendroica pensylvamca. Geothlypis trichas, Zonotrichia albicollis, Oporornis Philadelphia showed strong clumping of their small (< 0 5 ha) territories in logged patches and were absent or rare in undisturbed forest Eleven species (e g Seiurus aurocapillus, Vireo ohvaceus) tended to avoid logged areas, especially the centers of cut patches An additional 17 species fell between these two extremes, using a mixture of disturbed and undisturbed forest and showing no tendency to prefer one or the other These 17 species tended to have larger (1 to > 3 ha) territories than disturbance specialists We used ordination and quantitative matrix comparisons to describe and test relationships among 14 of the most common bird species according to their similarities in territory habitat structure, tree species composition, and foraging behavior These analyses did not reveal any strong associations between foraging behavior and use of cut versus uncut forest Habitat use by birds occupying this forest mosaic, with its strong local gradient of vegetation structure, was thus not associated with concurrent variation in foraging behavior The sizes of cut patches of forest (0 7-1 6 ha) in our study area may be close to the minimum required to attract distinct breeding assemblages of non-forest birds to otherwise undisturbed forest ecosystems Bird species that use patches of early-successional vegetation embedded m a forested landscape may adopt a fugitive strategy as they seek nesting habitats in the spring Careful use of forest management techniques may permit both forest-interior and early-successional bird species to coexist m the landscape     

Network analyses support the role of prey preferences in shaping resource use patterns within five animal populations

Individual variation is an inherent aspect of animal populations and understanding the mechanisms shaping resource use patterns within populations is crucial to comprehend how individuals partition resources. Theory predicts that differences in prey preferences among consumers and/or differences in the likelihood of adding new resources to their diets are key mechanisms underlying intrapopulation variation in resource use. We developed network models based on optimal diet theory that simulate how individuals consume resources under varying scenarios of individual variation in prey preferences and in the willingness of consuming alternate resources. We then investigated how the structure of individual–resource networks generated under each model compared to the structure of observed networks representing five classical examples of individual diet variation. Our results support the notion that, for the studied populations, individual variation in prey preferences is the major factor explaining patterns in individual–resource networks. In contrast, variation in the willingness of adding prey does not seem to play an important role in shaping patterns of resource use. Individual differences in prey preferences in the studied populations may be generated by complex behavioral rules related to cognitive constraints and experience. Our approach provides a pathway for mapping foraging models into network patterns, which may allow determining the possible mechanisms leading to variation in resource use within populations.     

Context-dependent specialisation drives temporal dynamics in intra- and inter-individual variation in foraging behaviour within a generalist bird population

Individual niche variation is common within animal populations, and has significant implications for a wide range of ecological and evolutionary processes. However, individual niche differences may also temporally vary as a result of behavioural plasticity. While it is well understood how niche variation is affected by changes in resource availability, comparatively little is known about the extent to which individual niche differences may vary within the annual cycle due to internal drivers. Here, we assess how time- and energy-constraints imposed by incubating and brood rearing affect inter- and intra-individual variation in the foraging behaviour of lesser black-backed gulls, a generalist seabird with strong individual niche variation. To this end, we compared daily foraging trips of 22 breeding and 23 non-breeding GPS-tracked adult gulls from two colonies in the Southern Bight of the North Sea over the course of the breeding season. We find that breeding birds, unlike non-breeding ones, did indeed alter their foraging behaviour during the breeding season. Both sexes reduced their searching effort by increasingly revisiting earlier foraging locations, allowing for shorter and more frequent foraging trips. Breeding females also showed pronounced shifts in their habitat use and strongly specialised on urbanised foraging habitats throughout the breeding season. Hence, while individual variation in habitat use remained largely consistent within non-breeders and in breeding males, individual variation among breeding females almost completely disappeared. Female lesser black-backed gulls are on average smaller, and therefore often outcompeted by males for the most profitable food sources. The temporal specialisation on spatially reliable anthropogenic food sources during breeding hence suggests a complex interplay between intrinsic competitive constraints, resource reliability and shifting time- and energy budges in shaping temporal dynamics in individual niche variation within our study population.     

Effects of connectivity and recurrent local disturbances on community structure and population density in experimental metacommunities

Metacommunity theory poses that the occurrence and abundance of species is a product of local factors, including disturbance, and regional factors, like dispersal among patches. While metacommunity ideas have been broadly tested there is relatively little work on metacommunities subject to disturbance. We focused on how localized disturbance and dispersal interact to determine species composition in metacommunities. Experiments conducted in simple two-patch habitats containing eight protozoa and rotifer species tested how dispersal altered community composition in both communities that were disturbed and communities that connected to refuge communities not subject to disturbance. While disturbance lowered population densities, in disturbed patches connected to undisturbed patches this was ameliorated by immigration. Furthermore, species with high dispersal abilities or growth rates showed the fastest post-disturbance recovery in presence of immigration. Connectivity helped to counteract the negative effect of disturbances on local populations, allowing mass-effect-driven dispersal of individuals from undisturbed to disturbed patches. In undisturbed patches, however, local population sizes were not significantly reduced by emigration. The absence of a cost of dispersal for undisturbed source populations is consistent with a lack of complex demography in our system, such as age- or sex-specific emigration. Our approach provides an improved way to separate components of population growth from organisms' movement in post-disturbance recovery of (meta)communities. Further studies are required in a variety of ecosystems to investigate the transient dynamics resulting from disturbance and dispersal.     

Female Spider Monkeys (<Emphasis Type="Italic">Ateles geoffroyi</Emphasis>) Cope with Anthropogenic Disturbance Through Fission–Fusion Dynamics

Most primates live in habitats with some level of anthropogenic disturbance, and such disturbances have a larger impact on frugivorous primates that are more sensitive to ecological disruptions than folivores. Fecal glucocorticoid metabolites provide insight into how the external environment affects internal physiological state, and thus provide information on how anthropogenic pressures become embodied. Here, I examine how subgroup size and glucocorticoids vary with high and low fruit abundance, and how fruit abundance, subgroup size, and activity budget affect fecal glucocorticoid metabolites in female spider monkeys (Ateles geoffroyi) living in an anthropogenically disturbed habitat. I measured these variables via behavioral, ecological, and fecal sampling for 15 months in 17 female spider monkeys at El Zota Biological Field Station. Subgroup size was significantly larger during periods of high fruit abundance, but glucocorticoids did not differ between periods of low and high fruit abundance. Monthly fruit abundance predicted subgroup sizes significantly, but did not predict fecal glucocorticoid concentrations. Increased resting time and reproductive state predicted fecal glucocorticoid concentrations significantly, but travel and foraging time had no significant effect on glucocorticoid concentrations. Individual resting time over the study period correlated negatively with glucocorticoid concentrations. These results suggest that spider monkeys cope with variation in fruit abundance by adjusting subgroup size, and that these adjustments may mitigate environmental stress in this mildly seasonal environment. The large, relatively productive forest size at this site, and the availability of anthropogenic food sources, enable this population of spider monkeys to cope with human-induced habitat disturbance.     

Collective Vigilance in the Wintering Hooded Crane: The Role of Flock Size and Anthropogenic Disturbances in a Human‐Dominated Landscape

Vigilance achieved at the group level, known as collective vigilance, can enhance the ability to assess threats and confer benefits to gregarious prey species. Examining the factors that influence collective vigilance and exploring how individual vigilance is organized at the group level can help to understand how prey groups respond to potential threats. We quantified collective vigilance and determined its temporal pattern in a natural wintering population of the hooded crane Grus monacha in the Shengjin Lake reserve in China. We examined the role of flock size and anthropogenic disturbances in the human‐dominated landscape on collective vigilance and level of synchronization. The proportion of time during which at least one individual scanned the surroundings (collective vigilance) increased with flock size and was higher in the more disturbed buffer zone of the lake. Synchronization of vigilance occurred more frequently in the smaller flocks but was not related to the risk of disturbance. Synchronization implies that individuals tend to monitor and copy the vigilance of neighbors. In the degraded wetlands, the wintering hooded crane benefits from foraging in groups and synchronizing their vigilance in response to human disturbances.     

Activity Budgets Derived From Time-Depth Recorders in a Diving Mammal

Abstract: We describe a method to convert continuously collected time-depth data from archival time-depth recorders (TDRs) into activity budgets for a benthic-foraging marine mammal. We used data from 14 TDRs to estimate activity-specific time budgets in sea otters (Enhydra lutris) residing near Cross Sound, southeast Alaska, USA. From the TDRs we constructed a continuous record of behavior for each individual over 39-46 days during summer of 1999. Behaviors were classified as foraging (diving to the bottom), other diving (traveling, grooming, interacting), and nondiving (assumed resting). The overall average activity budget (proportion of 24-hr/d) was 0.37 foraging (8.9 hr/d), 0.11 in other diving (2.6 hr/d), and 0.52 nondiving time (12.5 hr/d). We detected significant differences in activity budgets among individuals and between groups within our sample. Historically, the sea otter population in our study area had been expanding and sequentially reoccupying vacant habitat since their reintroduction to the area in the 1960s, and our study animals resided in 2 adjacent yet distinct locations. Males (n = 5) and individuals residing in recently occupied habitat (n = 4) spent 0.28-0.30 of their time foraging (6.7-7.2 hr/d), 0.17-0.18 of their time in other diving behaviors (4.1-4.3 hr/d), and 0.53-0.54 of their time resting (12.7-13.0 hr/d). In contrast, females (n = 9) and individuals residing in longer occupied habitat (n = 10) spent 0.40 of their time foraging (9.6 hr/d), 0.08-0.09 of their time in other diving behaviors (1.9-2.2 hr/d), and 0.51-0.52 of their time resting (12.2-12.5 hr/d). Consistent with these differences, sea otters residing in more recently occupied habitat captured more and larger clams (Saxidomus spp., Protothaca spp., Macoma spp., Mya spp., Clinocardium spp.) and other prey, and intertidal clams were more abundant and larger in this area. We found that TDRs provided data useful for measuring activity time budgets and behavior patterns in a diving mammal over long and continuous time periods. Fortuitous contrasts in time budgets between areas where our study animals resided suggest that activity time budgets estimated from TDRs may be a sensitive indicator of population status, particularly in relation to prey availability.