Variation in diurnal patterns of singing activity between urban and rural great tits

Microbial Biotechnolog

Male song stability shows cross‐year repeatability but does not affect reproductive success in a wild passerine bird

Abstract Predictable behaviour (or ‘behavioural stability’) might be favoured in certain ecological contexts, for example when representing a quality signal. Costs associated with producing stable phenotypes imply selection should favour plasticity in stability when beneficial. Repeatable among‐individual differences in degree of stability are simultaneously expected if individuals differ in ability to pay these costs, or in how they resolve cost–benefit trade‐offs. Bird song represents a prime example, where stability may be costly yet beneficial when stable singing is a quality signal favoured by sexual selection. Assuming energetic costs, ecological variation (e.g. in food availability) should result in both within‐ and among‐individual variation in stability. If song stability represents a quality signal, we expect directional selection favouring stable singers. For a 3‐year period, we monitored 12 nest box plots of great tits Parus major during breeding. We recorded male songs during simulated territory intrusions, twice during their mate's laying stage and twice during incubation. Each preceding winter, we manipulated food availability. Assuming that stability is costly, we expected food‐supplemented males to sing more stable songs. We also expected males to sing more stable songs early in the breeding season (when paternity is not decided) and stable singers to have increased reproductive success. We found strong support for plasticity in stability for two key song characteristics: minimum frequency and phrase length. Males were plastic because they became more stable over the season, contrary to expectations. Food supplementation did not affect body condition but increased stability in minimum frequency. This treatment effect occurred only in 1 year, implying that food supplementation affected stability only in interaction with (unknown) year‐specific ecological factors. We found no support for directional, correlational or fluctuating selection on the stability in minimum frequency (i.e. the song trait whose stability exhibited cross‐year repeatability): stable singers did not have higher reproductive success. Our findings imply that stability in minimum frequency is not a fitness quality indicator unless males enjoy fitness benefits via pathways not studied here. Future studies should thus address the mechanisms shaping and maintaining individual repeatability of song stability in the wild. </jats:p

Does song overlap signal aggressiveness?: An experimental study with repeated measures in free-ranging great tits

Vocal communication is often used to signal willingness to escalate into a physical fight during territorial conflicts. In songbirds, starting to sing when an opponent already sings (song overlapping) has been suggested to signal aggressive intent (willingness to escalate). We used a multiyear data set to test whether song overlapping predicts aggressiveness in great tits, Parus major. Territorial males were subjected twice to a simulated territorial intrusion when their mate was in the egg-laying phase, and twice when she was incubating. Males were presented with a taxidermic mount and a noninteractive playback of a conspecific song near their nestbox. The experiment was conducted over 3 consecutive years, resulting in repeated measures for males that bred across multiple years. The estimated minimum approach distance to the intruder, a repeatable and heritable trait that predicts the likelihood of physical attack, was used as a measure of aggression. We determined the duration of song overlapping by the focal male relative to values expected by chance. Against expectations, we found that birds that over -lapped were less (rather than more) aggressive. In addition, variance partitioning demonstrated that this link resulted from a within-individual effect: when birds became less aggressive from one observation to the next, they also overlapped more. There was no among-individual effect: individuals that were on average more aggressive did not, on average, overlap either more or less than others. Our results thus imply that song overlapping is linked to aggression but opposite to expectations, and not among in-dividuals. Furthermore, the majority of birds overlapped at or below chance levels. Overall, song over-lapping may not signal aggressive intent but rather 'nonengagement', or result from interference avoidance, allowing aggressive residents to better hear an intruder's acoustic output during territorial intrusions. (c) 2021 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.Animal science

The Behavioural Response of Australian Fur Seals to Motor Boat Noise

Australian fur seals breed on thirteen islands located in the Bass Strait, Australia. Land access to these islands is restricted, minimising human presence but boat access is still permissible with limitations on approach distances. Thirty-two controlled noise exposure experiments were conducted on breeding Australian fur seals to determine their behavioural response to controlled in-air motor boat noise on Kanowna Island (39°10′S, 146°18′E). Our results show there were significant differences in the seals' behaviour at low (64–70 dB) versus high (75–85 dB) sound levels, with seals orientating themselves towards or physically moving away from the louder boat noise at three different sound levels. Furthermore, seals responded more aggressively with one another and were more alert when they heard louder boat noise. Australian fur seals demonstrated plasticity in their vocal responses to boat noise with calls being significantly different between the various sound intensities and barks tending to get faster as the boat noise got louder. These results suggest that Australian fur seals on Kanowna Island show behavioural disturbance to high level boat noise. Consequently, it is recommended that an appropriate level of received boat sound emissions at breeding fur seal colonies be below 74 dB and that these findings be taken into account when evaluating appropriate approach distances and speed limits for boats

Anthropogenic noise is associated with changes in acoustic but not visual signals in red-winged blackbirds

Some birds in noisy areas produce songs with higher frequency and/or amplitude and altered timing compared to individuals in quiet areas. These changes may function to increase the efficacy of acoustic signals by reducing masking by noise. We collected audio recordings of red-winged blackbirds and measured noise levels. We found that males in noisier places produced songs with fewer syllables and slower repeat rate of elements in some components (rattles). Birds may also improve the efficacy of communication in noise by increasing usage of other signaling modalities. Red-winged blackbirds also perform a visual display in different intensities while singing. We also tested whether this species performs the visual display in different intensities according to current noise levels, and predicted that if the efficacy of songs is impaired in noisy places, males would compensate by performing a more intense visual display. For this, we also collected visual recordings from the same males from which we obtained acoustic recordings. We found no association between acoustic noise and the intensity of the visual display; thus, our results do not support the idea that males are using the visual display as a backup signal to communicate under acoustic noise. We discuss some possible explanations of this negative finding and for the observed noise-related changes in song length and rattle rate in the context of communication under noise

The role of singing style in song adjustments to fluctuating sound conditions: A comparative study on Mexican birds

Many bird species adjust their songs to noisy urban conditions by which they reduce masking and counteract the detrimental impact on signal efficiency. Different species vary in their response to level fluctuations of ambient noise, but it remains unclear why they vary. Here, we investigated whether noise-dependent flexibility may relate to singing style and signal function of the flexible acoustic trait. Species with highly variable songs may generally be more flexible and strongly repetitive singers may be more limited to stray from their stringent patterns. We exposed males of four passerine species with contrasting singing styles (repertoire size, immediate or eventual variety singing and syllable diversity) to three experimental sound conditions: 1) continuous urban noise; 2) intermittent white noise and 3) conspecific song playback. We found no spectral or temporal changes in response to experimental noise exposure in any of the four species, but significant temporal adjustment to conspecific playback in one of them. We argue that the consistency in song frequency and timing may have signal value, independent of singing style, and therefore be an explanation for the general lack of noise-dependent flexibility in the four species of the current study.Animal science