Biology subjects

Leu, S. T.

Publications and source records attributed to Leu, S. T..

5 recordsLinked to original sources

bioRxiv2024

Robust encoding of acoustic identity in alpaca hums - a basis for individual recognition

Individual recognition is an important element of social interactions among animals. While the presence of individually distinct vocalisations (providing a basis for individual recognition) has been widely tested across species, information about which components of a call encode this information is lacking. We investigated whether female alpaca (Vicugna pacos) vocalisations, particularly their hums, encode information about individual identity and explored which parameters contribute to this encoding. We recorded vocalisations from 9 adult female alpaca and extracted both spectro-temporal features (frequencies and duration) and mel-frequency cepstral coefficients (MFCC). Random forest analyses revealed clear individual differences in both datasets, with the spectro-temporal features allowing for slightly more accurate classification than MFCC (71% and 66.5% accuracy for spectro-temporal features and MFCC, respectively). These robust acoustic identities have the potential to provide a basis for individual recognition in alpaca, which could have important flow on effects for alpaca communication, as it allows receivers to modulate their response to the callers identity. Alpaca, as herd-living and vocal animals, provide an excellent model system for better understanding the mechanisms, causes and consequences of recognition and inter-individual communication.

animal behavior and cognition↗

bioRxiv2024

Same data, different results? Evaluating machine learning approaches for individual identification in animal vocalisations

Automated acoustic analysis is increasingly used in behavioural ecology, and determining caller identity is a key element for many investigations. However, variability in feature extraction and classification methods limits the comparability of results across species and studies, constraining conclusions we can draw about the ecology and evolution of the groups under study. We investigated the impact of using different feature extraction (spectro-temporal measurements, linear and Mel-frequency cepstral coefficients, as well as highly comparative time-series analysis) and classification methods (discriminant function analysis, neural networks, random forests, and support vector machines) on the consistency of caller identity classification accuracy across 16 mammalian datasets. We found that Mel-frequency cepstral coefficients and random forests yield consistently reliable results across datasets, facilitating a standardised approach across species that generates directly comparable data. These findings remained consistent across vocalisation sample sizes and number of individuals considered. We offer guidelines for processing and analysing mammalian vocalisations, fostering greater comparability, and advancing our understanding of the evolutionary significance of acoustic communication in diverse mammalian species.

animal behavior and cognition↗

bioRxiv2023

Environmental Uncertainty Affects Movement and Space-use in Sheep

Animals constantly experience periods of uncertainty due to seasonal changes in food distribution. The changing climate results in more variable weather patterns, which in turn alter environmental conditions, and can result in resource distribution being less predictable in space and time. How animals respond to these uncertain conditions, in particular the changing distribution of food resources, remains largely unclear and is an important question in the field of movement and animal ecology. Here we used an experimental approach to study how Merino sheep (Ovis aries) responded to different levels of environmental uncertainty in a drought-impacted region of the Australian arid zone. Sheep were unfamiliar with the experimental resource distribution at the start and progressively decreased their uncertainty (i.e., increased their environmental knowledge) when discovering an increasing number of foraging patches. We tracked 50 sheep with GPS collars (1 location every 15 sec) and deduced their movement and space use behaviour. When environmental uncertainty decreased, individuals moved more directionally (greater step length, smaller turn angles) and moved greater distances per day. They also had larger daily home ranges but rested in similar areas on consecutive nights (similar displacement, with the exception when five patches were discovered). Our study demonstrates how an arid zone, free-ranging ungulate adjusts its movement and space use behaviour as it gains environmental information in order to forage efficiently during periods of uncertainty. Our study provides important insights into how animals cope with variable environments and different levels of uncertainty.

animal behavior and cognition↗

bioRxiv2023

Using social information improves individual foraging efficiency in sheep

Knowledge about the environment is fundamentally important to move, find resources and forage efficiently. This information can either be acquired through individual exploration (personal information) or from other group members (social information). We experimentally assessed the use of social information and its influence on foraging efficiency in sheep, Ovis aries. Naive individuals paired with an informed partner that knew the food patch location, found the patch significantly faster compared to naive individuals paired with another naive individual. Similarly, they spent a significantly lower proportion of time exploring areas away from the food patch. We further found that the previous outcome of using social information (success = access to feed vs failure = no access to feed) had no impact and sheep continued to use social information in subsequent foraging trials and foraged similarly efficient. Our results suggest, naive sheep that are unfamiliar with resource locations, forage more efficiently when informed individuals are present compared to when all individuals are naive. If informed individuals play a similar role in larger groups, new management practices could be developed to improve foraging efficiency when sheep are moved to new paddocks or in paddocks with heterogenous and dynamic resource distribution.

animal behavior and cognition↗

bioRxiv2023

Heat stress conditions affect the social network structure of free-ranging sheep

Extreme weather conditions, like heatwave events, are becoming more frequent with climate change. Animals often modify their behaviour to cope with environmental changes and extremes. If the environmental conditions influence the trade-off between an individuals social propensity and optimal thermoregulation through shade use for instance, then divergent social decisions may be made. Hence, such behavioural changes have the potential to influence an individuals position in its social network, and the social network structure as a whole. We investigated whether heat stress conditions (quantified through the Temperature Humidity Index) and the resulting use of shaded areas, influences the social network structure and an individuals position in it. We studied this in free-ranging sheep in the arid zone of Australia, GPS-tracking all 48 individuals in a flock. When heat stress conditions worsened, individuals spent more time in the shade and the network was more connected (higher density) and less modular. Furthermore, an individuals social connectivity scaled with its shade use behaviour. Interestingly, individuals with intermediate shade use were most strongly connected (degree, strength, betweeness), indicating their importance for the connectivity of the social network during heat stress conditions. Our study shows that heat stress conditions, which are predicted to increase in severity and frequency due to climate change, influence the resource use within the ecological environment. This has flow on effects for the animals social environment through the changed social network structure. Significance statementDue to climate change, animals experience heat stress conditions more frequently. When ambient temperatures are high, individuals can seek shaded areas to mitigate the effect. However, whether these behavioural changes affect the interaction patterns in social species is not well understood. We tracked all individuals in a flock of sheep using GPS collars. We demonstrate that when heat stress conditions worsened (higher temperature humidity index), individuals spent more time in the shade and the social network was more connected with less internal structure. Furthermore, an individuals social connectivity scaled with its shade use behaviour, and individuals with intermediate shade use were most strongly connected in their social network. Our findings illustrate that individuals respond to climate change induced environmental conditions and that this has flow on effects for their social connectivity and the social network of the group.

animal behavior and cognition↗