How to treat mixed behavior segments in supervised machine learning of behavioural modes from inertial measurement data.

The application of supervised machine learning methods to identify behavioural modes from inertial measurements of bio-loggers has become a standard tool in behavioural ecology. Several design choices can affect the accuracy of identifying the behavioural modes. One such choice is the inclusion or exclusion of segments consisting of more than a single behaviour (mixed segments) in the machine learning model training data. Currently, the common practice is to ignore such segments during model training. In this paper we tested the hypothesis that including mixed segments in model training will improve accuracy, as the model would perform better in identifying them in the test data. We test this hypothesis using a series of data simulations on four datasets of accelerometer data coupled with behaviour observations, obtained from four study species (Damaraland mole-rats, meerkats, olive baboons, polar bears). Results show that when a substantial proportion of the test data are mixed behaviour segments (above ~ 10%), including mixed segments in machine learning model training improves the accuracy of classification. These results were consistent across the four study species, and robust to changes in segment length, sample size, and degree of mixture within the mixed segments. However, we also find that in some cases (particularly in baboons) models trained with mixed segments show reduced accuracy in classifying test data containing only single behaviour (pure) segments, compared to models trained without mixed segments. Based on these results, we recommend that when the classification model is expected to deal with a substantial proportion of mixed behaviour segments (> 10%), it is beneficial to include them in model training, otherwise, it is unnecessary but also not harmful. The exception is when there is a basis to assume that the training data contains a higher rate of mixed segments than the actual (unobserved) data to be classified-such a situation may occur particularly when training data are collected in captivity and used to classify data from the wild. In this case, excess inclusion of mixed segments in training data should probably be avoided.

Pregnancy reduces concurrent pup care behaviour in meerkats, generating differences between dominant and subordinate females.

In some mammals, and particularly in cooperative breeding ones, successive bouts of reproduction can overlap so that a female is often pregnant while still nurturing dependent young from her previous litter. Such an overlap requires females to divide their energetic budget between two reproductive activities, and pregnancy costs would consequently be expected to reduce investment in concurrent offspring care. However, explicit evidence for such reductions is scarce, and the potential effects they may have on work division in cooperative breeders have not been explored. Using 25 years of data on reproduction and cooperative behaviour in wild Kalahari meerkats, supplemented with field experiments, we investigated whether pregnancy reduces contributions to cooperative pup care behaviours, including babysitting, provisioning and raised guarding. We also explored whether pregnancy, which is more frequent in dominants than subordinates, could account for the reduced contributions of dominants to the cooperative pup care behaviours. We found that pregnancy, particularly at late stages of gestation, reduces contributions to cooperative pup care; that these reductions are eliminated when the food available to pregnant females is experimentally supplemented; and that pregnancy effects accounted for differences between dominants and subordinates in two of the three cooperative behaviours examined (pup provisioning and raised guarding but not babysitting). By linking pregnancy costs with reductions in concurrent pup care, our findings illuminate a trade-off between investment in successive, overlapping bouts of reproduction. They also suggest that some of the differences in cooperative behaviour between dominant and subordinate females in cooperative breeding mammals can be a direct consequence of differences in their breeding frequency.

Individual environmental niches in mobile organisms.

Individual variation is increasingly recognized as a central component of ecological processes, but its role in structuring environmental niche associations remains largely unknown. Species' responses to environmental conditions are ultimately determined by the niches of single individuals, yet environmental associations are typically captured only at the level of species. Here, we develop scenarios for how individual variation may combine to define the compound environmental niche of populations, use extensive movement data to document individual environmental niche variation, test associated hypotheses of niche configuration, and examine the consistency of individual niches over time. For 45 individual white storks (Ciconia ciconia; 116 individual-year combinations), we uncover high variability in individual environmental associations, consistency of individual niches over time, and moderate to strong niche specialization. Within populations, environmental niches follow a nested pattern, with individuals arranged along a specialist-to-generalist gradient. These results reject common assumptions of individual niche equivalency among conspecifics, as well as the separation of individual niches into disparate parts of environmental space. These findings underscore the need for a more thorough consideration of individualistic environmental responses in global change research.

Group size increases inequality in cooperative behaviour.

In cooperatively breeding species where rearing effort is shared among multiple group members, increases in group size typically reduce average per capita contributions to offspring care by all group members (load-lightening) but it is not known how changes in group size affect the distribution of workload among group members. The socioeconomic collective action theory suggests that, in larger groups, the incentives for free riding are stronger, leading to greater inequalities in work division among group members. Here, we use the Gini index to measure inequality at the group level in the contributions of helpers to three different cooperative behaviours (babysitting, pup-provisioning and raised guarding) in groups of varying size in wild Kalahari meerkats (Suricata suricatta). In larger groups, inequality in helpers' contributions to cooperative activities and the frequency of free riding both increased. Elevated levels of inequality were generated partly as a result of increased differences in contributions to cooperative activities between helpers in different sex and age categories in larger groups. After controlling for the positive effect of group size on total provisioning, increasing levels of inequality in contributions were associated with reductions in total pup-provisioning conducted by the group. Reductions in total pup-provisioning were, in turn, associated with reductions in the growth and survival of pups (but pup growth and survival were not directly affected by inequality in provisioning). Our results support the prediction of collective action theory described above and show how the Gini index can be used to investigate the distribution of cooperative behaviour within the group.

Early-life behaviour predicts first-year survival in a long-distance avian migrant.

Early-life conditions have critical, long-lasting effects on the fate of individuals, yet early-life activity has rarely been linked to subsequent survival of animals in the wild. Using high-resolution GPS and body-acceleration data of 93 juvenile white storks (Ciconia ciconia), we examined the links between behaviour during both pre-fledging and post-fledging (fledging-to-migration) periods and subsequent first-year survival. Juvenile daily activity (based on overall dynamic body acceleration) showed repeatable between-individual variation, the juveniles' pre- and post-fledging activity levels were correlated and both were positively associated with subsequent survival. Daily activity increased gradually throughout the post-fledging period, and the relationship between post-fledging activity and survival was stronger in individuals who increased their daily activity level faster (an interaction effect). We suggest that high activity profiles signified individuals with increased pre-migratory experience, higher individual quality and perhaps more proactive personality, which could underlie their superior survival rates. The duration of individuals' fledging-to-migration periods had a hump-shaped relationship with survival: higher survival was associated with intermediate rather than short or long durations. Short durations reflect lower pre-migratory experience, whereas very long ones were associated with slower increases in daily activity level which possibly reflects slow behavioural development. In accordance with previous studies, heavier nestlings and those that hatched and migrated earlier had increased survival. Using extensive tracking data, our study exposed new links between early-life attributes and survival, suggesting that early activity profiles in migrating birds can explain variation in first-year survival.

Seasonal niche tracking of climate emerges at the population level in a migratory bird.

Seasonal animal migration is a widespread phenomenon. At the species level, it has been shown that many migratory animal species track similar climatic conditions throughout the year. However, it remains unclear whether such a niche tracking pattern is a direct consequence of individual behaviour or emerges at the population or species level through behavioural variability. Here, we estimated seasonal niche overlap and seasonal niche tracking at the individual and population level of central European white storks (Ciconia ciconia). We quantified niche tracking for both weather and climate conditions to control for the different spatio-temporal scales over which ecological processes may operate. Our results indicate that niche tracking is a bottom-up process. Individuals mainly track weather conditions while climatic niche tracking mainly emerges at the population level. This result may be partially explained by a high degree of intra- and inter-individual variation in niche overlap between seasons. Understanding how migratory individuals, populations and species respond to seasonal environments is key for anticipating the impacts of global environmental changes.

Early arrival at breeding grounds: Causes, costs and a trade-off with overwintering latitude.

Early arrival at breeding grounds is of prime importance for migrating birds as it is known to enhance breeding success. Adults, males and higher quality individuals typically arrive earlier, and across years, early arrival has been linked to warmer spring temperatures. However, the mechanisms and potential costs of early arrival are not well understood. To deepen the understanding of arrival date differences between individuals and years, we studied them in light of the preceding spring migration behaviour and atmospheric conditions en route. GPS and body acceleration (ACC) data were obtained for 35 adult white storks (Ciconia ciconia) over five years (2012-2016). ACC records were translated to energy expenditure estimates (overall dynamic body acceleration; ODBA) and to behavioural modes, and GPS fixes were coupled with environmental parameters. At the interindividual level (within years), early arrival was attributed primarily to departing earlier for migration and from more northern wintering sites (closer to breeding grounds), rather than to migration speed. In fact, early-departing birds flew slower, experienced weaker thermal uplifts and expended more energy during flight, but still arrived earlier, emphasizing the cost and the significance of early departure. Individuals that wintered further south arrived later at the breeding grounds but did not produce fewer fledglings, presumably due to positive carry-over effects of advantageous wintering conditions (increased precipitation, vegetation productivity and daylight time). Therefore, early arrival increased breeding success only after controlling for wintering latitude. Males arrived slightly ahead of females. Between years, late arrival was linked to colder temperatures en route through two different mechanisms: stronger headwinds causing slower migration and lower thermal uplifts resulting in longer stopovers. This study showed that distinct migratory properties underlie arrival time variation within and between years. It highlighted (a) an overlooked cost of early arrival induced by unfavourable atmospheric conditions during migration, (b) an important fitness trade-off in storks between arrival date and wintering habitat quality and (c) mechanistic explanations for the negative temperature-arrival date correlation in soaring birds. Such understanding of arrival time can facilitate forecasting migrating species responses to climate changes.

Extra-pair paternity in the socially monogamous white stork (Ciconia ciconia) is fairly common and independent of local density.

Although many birds are socially monogamous, most (>75%) studied species are not strictly genetically monogamous, especially under high breeding density. We used molecular tools to reevaluate the reproductive strategy of the socially monogamous white stork (Ciconia ciconia) and examined local density effects. DNA samples of nestlings (Germany, Spain) were genotyped and assigned relationships using a two-program maximum likelihood classification. Relationships were successfully classified in 79.2% of German (n = 120) and 84.8% of Spanish (n = 59) nests. For each population respectively, 76.8% (n = 73) and 66.0% (n = 33) of nests contained only full-siblings, 10.5% (n = 10) and 18.0% (n = 9) had half-siblings (at least one nestling with a different parent), 3.2% (n = 3) and 10.0% (n = 5) had unrelated nestlings (at least two nestlings, each with different parents), and 9.5% (n = 9) and 6.0% (n = 3) had "not full-siblings" (could not differentiate between latter two cases). These deviations from strict monogamy place the white stork in the 59(th) percentile for extra-pair paternity among studied bird species. Although high breeding density generally increases extra-pair paternity, we found no significant association with this species' mating strategies. Thus although genetic monogamy is indeed prominent in the white stork, extra-pair paternity is fairly common compared to other bird species and cannot be explained by breeding density.

The challenges of the first migration: movement and behaviour of juvenile vs. adult white storks with insights regarding juvenile mortality.

Migration conveys an immense challenge, especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration presumably for navigational purposes, also display much lower annual survival than adults. Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behaviour and energy expenditure (estimated from overall dynamic body acceleration) and placed this in the context of the juveniles' lower survival rate. Juveniles used flapping flight vs. soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for their higher flight costs by increased refuelling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality. Our findings demonstrate the conflict between the juveniles' inferior flight skills and their urge to keep up with mixed adult-juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants and that natural selection is operating on juvenile variation in flight efficiency.

Costs of migratory decisions: A comparison across eight white stork populations.

Annual migratory movements can range from a few tens to thousands of kilometers, creating unique energetic requirements for each specific species and journey. Even within the same species, migration costs can vary largely because of flexible, opportunistic life history strategies. We uncover the large extent of variation in the lifetime migratory decisions of young white storks originating from eight populations. Not only did juvenile storks differ in their geographically distinct wintering locations, their diverse migration patterns also affected the amount of energy individuals invested for locomotion during the first months of their life. Overwintering in areas with higher human population reduced the stork's overall energy expenditure because of shorter daily foraging trips, closer wintering grounds, or a complete suppression of migration. Because migrants can change ecological processes in several distinct communities simultaneously, understanding their life history decisions helps not only to protect migratory species but also to conserve stable ecosystems.

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

BACKGROUND: The 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. DESCRIPTION: Here 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. CONCLUSIONS: AcceleRater provides the means to identify animal behavior, offering a user-friendly tool for ACC-based behavioral annotation, which will be dynamically upgraded and maintained.

Foraging sequence, energy intake and torpor: an individual-based field study of energy balancing in desert golden spiny mice.

We studied the relationship between sequence of foraging, energy acquired and use of torpor as an energy-balancing strategy in diurnally active desert golden spiny mice. We hypothesised that individuals that arrive earlier to forage will get higher returns and consequently spend less time torpid. If that is the case, then early foragers can be viewed as more successful; if the same individuals arrive repeatedly early, they are likely to have higher fitness under conditions of resource limitation. For the first time, we show a relationship between foraging sequence and amount of resources removed, with individuals that arrive later to a foraging patch tending to receive lower energetic returns and to spend more time torpid. Torpor bears not only benefits but also significant costs, so these individuals pay a price both in lower energy intake and in extended periods of torpor, in what may well be a positive feedback loop.

Light masking in the field: an experiment with nocturnal and diurnal spiny mice under semi-natural field conditions.

Light masking has been studied almost exclusively in the laboratory. The authors populated four field enclosures with locally coexisting nocturnal Acomys cahirinus and diurnal A. russatus, and monitored their body temperatures (T(b)) using implanted temperature-sensitive radio transmitters. A 3-h light pulse was initiated at the beginning of two consecutive nights; preceding nights were controls. A. cahirinus T(b) and calculated activity levels decreased significantly during the light pulse, demonstrating a negative light masking response (light effect on T(b): -0.32 °C ± 0.15 °C; average calculated activity records during the light pulse: 7 ± 1.53, control: 9.8 ± 1.62). Diurnal A. russatus did not respond to the light pulse. We conclude that light masking is not an artifact of laboratory conditions but represents a natural adaptive response in free-living populations.