Biology subjects

Ridley, A. R.

Publications and source records attributed to Ridley, A. R..

11 recordsLinked to original sources

bioRxiv2026

Comprehension precedes production of a complex call sequence

Growing evidence of animals combining discrete, meaningful calls into sequences--a feature once thought unique to linguistic syntax--has presented the opportunity to investigate the evolutionary origins of syntactic communication. The arbitrary assignment of meaning to words marks an important step in human language evolution, and a necessary precursor to generating further meaning through sentences. Studying how other animals that produce call sequences learn the meaning of these signals could help shed light on how referentiality and semantic combinatoriality evolved. Given the presence of meaningful call sequences has only recently been revealed in several non-human animals, ontogenetic studies of the comprehension of these vocalisations are, to date, non-existent. Western Australian magpies (Gymnorhina tibicen dorsalis) combine discrete calls into a diverse array of call sequences. Recent evidence shows these sequences are socially learned, but the developmental stage at which fledglings respond correctly to them remains unstudied. We performed playbacks of a discrete alarm call and call sequence to fledglings over the course of their first 18 weeks out of the nest, identifying when they differentiate between the low-level disturbance associated with the discrete call and the high-grade aerial threat associated with the sequence. Fledglings showed immediate vigilance to both vocalisations but exhibited significantly greater vigilance and upward scanning following the sequence. Critically, fledglings showed this response to the sequence from the first week of testing, with no effect of age on the response to either vocalisation. These findings suggest that comprehension precedes production of sequences in magpies and that sequence meanings are either learned rapidly or have an innate basis. While further investigation is essential, this study offers the first empirical insight into the ontogenetic emergence of combinatorial comprehension in a non-human animal.

animal behavior and cognition↗

bioRxiv2026

Innate building blocks underly socially learned call sequences

Recent evidence of extensive call sequence use in non-human primates has led to the theory that syntax evolved to mitigate the constraints of their genetically fixed repertoires, before vocal production learning later emerged in humans. However, evidence of similarly extensive sequence repertoires in an open-ended vocal production learner--the Western Australian magpie (Gymnorhinatibicendorsalis)--offers a unique opportunity to explore potential alternative pathways to syntactic communication. Our previous work revealed fledgling magpies learn group-specific repertoires of structured call sequences from their social contacts, with more sociable individuals acquiring larger repertoires earlier in development. Notably however, the individual vocal segments that combine to form their calls and call sequences were shared across groups and emerged as early as the first week post-fledging--suggesting the underlying vocal elements may not be learned. Here we utilised acoustic neighbourhood-based dimensionality reduction to compare clustering patterns of vocal segments across magpie fledgling developmental stages, and between fledglings and adults. We found no evidence of acoustic development over time, and no significant distinction between fledgling and adult productions of the same vocal segments. The same coarticulatory effects--where a vocal element is produced differently when combined with another--and geographic variation established previously in adults were supported in fledglings too. These findings support that the vocal building blocks underpinning magpie call sequences are innate, suggesting usage learning better explains how fledglings learn to combine calls. In a species capable of open-ended production learning, this suggests learning to combine existing signals may be more adaptive than productively learning new ones. Rather than evolving solely to compensate for genetically fixed repertoires, syntax may have evolved as a flexible, convergent solution to the various challenges of expanding communicative capacity--whether due to genetic constraints, cognitive limitations or the cost of establishing new meaning in novel signals.

animal behavior and cognition↗

bioRxiv2026

Socially learned call sequences reveal gradual development of higher-order structure

Syntax was long considered to distinguish human language from other vocal systems, with parallels in non-human animals historically limited to song. However, song lacks discrete meaning, which is a crucial pre-requisite of linguistic syntax. Over the last two decades evidence of combinatoriality in the discrete, semantic calls of an array of taxa has accumulated, providing the opportunity to investigate potentially closer parallels to language. However, most examples remain limited to small repertoires of simple two-call sequences, preventing evidence of complex internal structuring like that seen in human sentences. The recent discovery that several species produce extensive repertoires of much longer call sequences, has provided the opportunity to investigate the full extent of syntactic structure in non-human call systems. Here we demonstrate that Western Australian magpies (Gymnorhina tibicen dorsalis) use multi-level structured ordering rules within their semantic call sequences and that these ordering rules are learned during development. Specifically, we find that calls within sequences up to 15 calls long depend on the two calls given prior and that independently produced segments ( phonemes), calls, and sequences recombine into longer structures, indicating hierarchical organisation. This represents the first evidence of multi-level non-adjacent organisation and learned syntactic structure in a semantic non-human system.

animal behavior and cognition↗

bioRxiv2024

Meta-analyses reveal support for the Social Intelligence Hypothesis

The Social Intelligence Hypothesis (SIH) is one of the leading explanations for the evolution of cognition. Since its inception a vast body of literature investigating the predictions of the SIH has accumulated, using a variety of methodologies and species. However, the generalisability of the hypothesis remains unclear. To gain an understanding of the robustness of the SIH as an explanation for the evolution of cognition, we systematically searched the literature for studies investigating the predictions of the SIH. Accordingly, we compiled 103 studies with 584 effect sizes from 17 taxonomic orders. We present the results of four meta-analyses which reveal support for the SIH across interspecific, intraspecific and developmental studies. However, effect sizes did not differ significantly between the cognitive or sociality metrics used, taxonomy or testing conditions. Thus, support for the SIH is similar across studies using neuroanatomy and cognitive performance, those using broad categories of sociality, group size and social interactions, across taxonomic groups, and for tests conducted in captivity or the wild. Overall, our meta-analyses support the SIH as an evolutionary and developmental explanation for cognitive variation.

animal behavior and cognition↗

bioRxiv2024

Anthropogenic noise affects vocalisation properties of the territorial song of Western Australian magpies

Anthropogenic noise is considered one of the most serious forms of pollution globally and has been shown to have negative effects on the distribution, behaviour, cognition and reproductive success of animal species worldwide. One of the most well researched impacts of anthropogenic noise is its effect on acoustic communication. Animals may adjust the rate, amplitude, duration, and/or frequency of their acoustic signals to better maintain communication when anthropogenic noise is present. In this study, we combine behavioural focals, amplitude measurements and audio recordings to investigate how female Western Australian magpies (Gymnorhina tibicen dorsalis) alter the acoustic features of their territorial song (known as a carol) when anthropogenic noise is present. Magpies reduced the rate at which they carolled when loud anthropogenic noise was present, and increased their peak frequency during anthropogenic noise, but, contrary to our hypotheses did not alter the amplitude, duration, or other frequency parameters of their carols. Results from this study add to the growing body of literature documenting changes to the vocal behaviour of wildlife in the presence of anthropogenic noise and highlights the importance of investigating multiple acoustic parameters to understand how species adjust their vocalisations in response to this pollutant.

animal behavior and cognition↗

bioRxiv2022

General cognitive performance declines with female age and is negatively related to fledging success in a wild bird

Identifying the causes and fitness consequences of intraspecific variation in cognitive performance is fundamental to understand how cognition evolves. Selection may act on different cognitive traits separately or jointly as part of the general cognitive performance of the individual. To date, few studies have examined simultaneously whether individual cognitive performance covaries across different cognitive tasks, the relative importance of individual and social attributes in determining cognitive variation, and its fitness consequences in the wild. Here, we tested 38 wild southern pied babblers (Turdoides bicolor) on a cognitive test battery targeting associative learning, reversal learning and inhibitory control. We found that a single factor explained 59.5% of the variation in individual cognitive performance across tasks, suggestive of a general cognitive factor. General cognitive performance varied by age and sex; declining with age in females but not males. Older females also tended to produce a higher average number of fledglings per year compared to younger females. Analysing over 10 years of breeding data, we found that individuals with lower general cognitive performance produced more fledglings per year. Collectively, our findings support the existence of a trade-off between cognitive performance and reproductive success in a wild bird.

animal behavior and cognition↗

bioRxiv2021

Hot days are associated with short-term adrenocortical responses in a Southern African arid-zone passerine bird.

Non-invasive methods for investigating the biological effects of environmental variables are invaluable for understanding potential impacts of climate change on behavioural and physiological stress responses of free-ranging animals. Foraging efficiency, body mass maintenance and breeding success are compromised in Southern pied babblers Turdoides bicolor exposed to air temperatures between ~35{degrees}C and ~40{degrees}C. We tested the hypothesis that these very hot days are acute stressors for free-ranging babblers by quantifying the relationship between daily maximum air temperature (Tmax) and faecal glucocorticoid metabolite (fGCM) levels. We collected naturally-excreted droppings from free-ranging pied babblers and analysed fGCM levels. Levels of fGCMs in droppings collected after 3pm were independent of same-day Tmax < 38 {degrees}C and averaged 140.25 ng g-1 Dry Weight {+/-} 56.92 ng g-1 DW (mean {+/-} SD) over this range. Above an inflection Tmax = 38 {degrees}C, however, fGCM levels increased linearly with same-day Tmax and averaged 190.79 ng g-1 DW {+/-} 70.13 ng g-1 DW. There was no relationship between Tmax on the previous day and fGCM levels in droppings collected the following morning. Group size, breeding stage, sex and rank did not predict variation in fGCM levels. These results suggest that very high Tmax may be linked to acute, but not chronic, heat stress responses. The fGCM levels we measured are likely to represent a biologically meaningful response to an environmental stressor (high Tmax), suggesting a physiological mechanism underlying observed changes in behaviour and reproductive success at high temperatures in this species.

physiology↗

bioRxiv2021

Direct and indirect effects of high temperatures on fledging success in a cooperatively breeding bird

High temperatures and low rainfall consistently constrain reproduction in arid-zone bird species. Understanding the mechanisms underlying this pattern is critical for predicting how climate change will influence population persistence and to inform conservation and management. In this study, we analysed Southern Pied Babbler Turdoides nestling survival, daily growth rate and adult investment behaviour during the nestling period over three austral summer breeding seasons. High temperatures were associated with lower body mass, shorter tarsi, and reduced daily growth rates of nestlings. Piecewise structural equation modelling suggests that direct impacts of temperature had the strongest influence, followed by changes in provisioning rates by adults to older nestlings. Adjustments to adult provisioning strategies did not compensate for direct negative effects of high air temperatures on nestling body mass, tarsus and wing length, or daily growth rates. Declining reproductive success during hot weather poses a potentially serious threat to population replacement and persistence as climate change progresses, even for currently common and widespread species. Significantly lower offspring survival as a result of climate warming will likely contribute to the collapse of animal communities well before temperatures regularly approach or exceed lethal tolerance limits. Detailed mechanistic data like these allow us to model the pathways by which high temperature causes nest failure. In turn, this could allow us to design targeted conservation action to effectively mitigate climate effects.

ecology↗

bioRxiv2020

Dehydration risk, not ambient incubation, limits nest attendance at high temperatures

High air temperatures have measurable negative impacts on reproduction in wild animal populations, including during incubation in birds. Understanding the mechanisms driving these impacts requires comprehensive knowledge of animal physiology and behaviour under natural conditions. We used a novel combination of a non-invasive doubly-labelled water technique and behaviour observations in the field to examine effects of temperature, rainfall, and group size on physiology and behaviour during incubation in southern pied babblers Turdoides bicolor, a cooperatively-breeding passerine endemic to a semi-arid region in southern Africa. The proportion of time that clutches of eggs were incubated declined as air temperatures increased, traditionally interpreted as a benefit of ambient incubation. However, we show that a) clutches were less likely to hatch when exposed to high air temperatures; b) pied babbler groups incubated their nests almost constantly (97% of daylight hours) except on hot days; c) operative temperatures in unattended nests were substantially higher than air temperatures and frequently exceeded 40.5{degrees}C, above which bird embryos are at risk of death; d) pied babblers incubating for long periods of time failed to maintain water balance on hot days but not cool days; and e) pied babblers from incubating groups did not maintain body mass on hot days. These results suggest that, rather than taking advantage of opportunities for ambient incubation, pied babblers leave the nests during hot periods to avoid dehydration as a consequence of incubating at high operative temperatures. As mean air temperatures increase and extreme heat events become more frequent under climate change, birds will likely incur greater water costs during incubation, leading to compromised nest attendance and increased likelihood of eggs overheating, with implications for nest success and, ultimately, population persistence.

ecology↗

bioRxiv2020

Hot droughts compromise interannual survival across all group sizes in a cooperatively breeding bird

Increasingly harsh and unpredictable climate regimes are affecting animal populations around the world as climate change advances. One relatively unexplored aspect of species vulnerability to climate change is whether and to what extent responses to environmental stressors might be mitigated by variation in group size in social species. We used a 15-year dataset for a cooperatively-breeding bird, the southern pied babbler Turdoides bicolor, to determine the impact of temperature, rainfall, and group size on body mass change and interannual survival in both juveniles and adults. Hot and dry conditions were associated with reduced juvenile growth, mass loss in adults, and compromised survival between years in both juveniles (-86%) and adults (-60%). Individuals across all group sizes experienced similar effects of climatic conditions. Larger group sizes may not buffer individual group members against the impacts of hot and dry conditions, which are expected to increase in frequency and severity in future.

ecology↗

bioRxiv2020

High temperatures drive offspring mortality in a cooperatively breeding bird

An improved understanding of life history responses to current environmental variability is required to predict species-specific responses to anthopogenic climate change. Previous research has suggested that cooperation in social groups may buffer individuals against some of the negative effects of unpredictable climates. We use a 15-year dataset on a cooperative-breeding arid-zone bird, the southern pied babbler Turdoides bicolor, to test i) whether environmental conditions and group size correlate with survival of young during three development stages (egg, nestling, fledgling), and ii) whether group size mitigates the impacts of adverse environmental conditions on reproductive success. Exposure to high mean daily maximum temperatures (mean Tmax) during early development was associated with reduced survival probabilities of young in all three development stages. No young survived when mean Tmax > 38{degrees}C across all group sizes. Low reproductive success at high temperatures has broad implications for recruitment and population persistence in avian communities given the rapid pace of advancing climate change. That impacts of high temperatures were not moderated by group size, a somewhat unexpected result given prevailing theories around the influence of environmental uncertainty on the evolution of cooperation, suggests that cooperative breeding strategies are unlikely to be advantageous in the face of rapid anthropogenic climate change.

ecology↗