Biology subjects

de Kort, S. R.

Publications and source records attributed to de Kort, S. R..

4 recordsLinked to original sources

bioRxiv2025

Song length competence: evidence for a new fitness indicator in birdsong

In animal displays, motor performance can provide key information to recipients associated with whole-organism condition. It has been argued that biomechanical processes constrain motor displays and performing near the phenotypic boundary can be an honest indicator of quality. Using data from 140 blue tits Cyanistes caeruleus, including male and female songs, we found a new phenotypic boundary defined by a trade-off between song length and note length. Male "song length competence" - a composite metric considering the trade-off with note length - peaked seasonally during the female fertile period and was positively associated with reproductive success. These findings support song length competence as a fitness indicator in blue tits. Recovery competence, a well-known composite metric assessing the efficacy to produce consecutive notes, showed similar seasonal and reproductive variation but with a much smaller impact on reproductive success. We further confirmed previously known trade-offs between 2) frequency modulation vs. note length and 3) frequency jumps vs. inter-note gaps between notes, but these metrics seemed biologically irrelevant with no significant variation in relation to season or individual fitness. We encourage further research on birdsong and other animal displays to shed light on the universality of these principles in the assessment of motor performance.

animal behavior and cognition↗

bioRxiv2023

Java sparrow song conforms to Mezerath's Law but not Zipf's Law of Abbreviation

Linguistic laws, which describe common statistical patterns in human language, are often studied in animal communication systems. Despite good evidence for adherence to these laws in non-human primate communication, there is still a paucity of data on other taxa. Birdsong is often used as a model for human language development due to similarities in vocal learning processes. Investigating whether birdsong also adheres to linguistic laws may provide further value or help determine the limitations of such comparisons. Here, we looked for patterns consistent with Menzeraths law, the tendency for longer sequences to be made up of smaller constituent parts, and Zipfs Law of Abbreviation, the tendency for more frequently used elements to be shorter in length, in the songs of Java sparrows (Padda oryzivora). We found that songs conformed to Menzeraths law at both the population and individual level; longer sequences were made up of shorter notes. This pattern was achieved through note type selection rather than the shortening of existing note types. Adherence to Menzeraths law may reflect species-specific constraints on song durations. We found no evidence to support adherence to Zipfs Law of Abbreviation, either at population or individual level; more frequently used notes were not shorter in length. However, as repertoire size in Java sparrows is small, we expect our power to detect Zipfs Law of Abbreviation to be weak. Whilst there may be some limitations in applying linguistic laws derived from human language to birdsong, especially Zipfs Law of Abbreviation, these laws may still provide insights into animal and human communication systems.

animal behavior and cognition↗

bioRxiv2023

Assessing the effect of zoo closure on the soundscape using multiple measures

The zoo soundscape has a number of important implications for animal welfare, management, and conservation. However, despite its importance, the zoo soundscape is yet to be examined in depth using multiple measures. Consistent human presence can influence the zoo soundscape. However, it is difficult to determine the specific impact of human presence, as visitors are usually present during the day when animals are active. The COVID-19 lockdown in 2020 provided a unique opportunity to study zoo soundscapes in the absence of visitors. We compared the sound environment during the 2020 closure period to a comparable open period in 2019 across three zoo aviaries, examining broad band frequency measures of sound pressure levels, sound pressure levels in defined frequency bands, and acoustic indices (Acoustic Complexity Index and Normalized Difference Soundscape Index) to describe the zoo soundscape. Acoustic indices have not, to our knowledge, previously been used in the zoo setting, although they may provide a useful metric to assess sound disturbance. Therefore, we also used this natural experiment to explore how successful these measures may be in assessing disturbances in captive environments. We found a significant effect of human presence on the sound environment; aviaries were generally quieter with less low frequency noise and with a greater proportion of biotic sound during the 2020 zoo closure period. We argue that NDSI could be a useful index for determining anthropogenic disturbance in zoos, although further information on how it is influenced by additional factors, such as human speech, would be beneficial. The use of multiple measures to assess the sound environment in zoos can provide additional information beyond loudness, such as frequencies where sound energy is concentrated and characteristics of the soundscape, which could be used to better target management and mitigation.

ecology↗

bioRxiv2021

Frequent female song in blue tits: behavioural context suggests a role in intrasexual competition

The blue tit (Cyanistes caeruleus) is an important avian model in evolutionary ecology (> 20,000 published scientific studies). Song, like in other songbird species, is generally described as a male trait and plays an important role in mate attraction and territory defence. Over the decades, there have been recurring reports of anecdotal female song but these have not led to any quantitative study of female song in blue tits. Our systematic sampling over three years revealed prolific female singing in a northern population of colour ringed blue tits. Daytime singing of females occurred throughout the breeding season during agonistic interactions, solo songs and alarm situations, and these contexts are similar to male song. Notably, female song was absent during the dawn chorus; the period around sunrise when males sing intensively just before mating. Female and male song overlapped substantially in acoustic structure (i.e. same song types, peak frequency or trill rates) but there were also significant differences in that females had smaller repertoires, shorter trills and lower vocal consistency. Differential selections pressures related with contextual (functional) differences in the role of male and female song could explain the observed differences in acoustic structure. The new finding of prolific female singing in such a well-studied species suggests we ought to revise our understanding of male and female vocal communication in this (and probably other) species. Identifying the selection pressures associated to the convergence versus divergence of male and female song may provide important insight in understanding birdsong evolution. Lay summaryFemale song has been anecdotally reported in blue tits but there are no quantitative studies of singing behaviour, song structure or context. Here, we report frequent female singing in blue tits, associated mostly with agonistic interactions and alarm situations. Importantly, female song was not observed during dawn chorus, the period around sunrise when males sing intensively just before mating. Female and male song overlapped substantially in acoustic structure (i.e. same song types) but there were also significant differences (i.e. females sang with lower vocal consistency). We speculate that differences in context (function) of male and female song could explain the observed differences in acoustic structure. The new finding of prolific female singing in such a well-studied species suggests we ought to revise our understanding of male and female vocal communication.

animal behavior and cognition↗