Long-term influence of simulated territorial intrusions on dawn and dusk singing in the Winter Wren: spring versus autumn

Males of many songbird species have peaks of singing activity at dawn and dusk. Singing during those twilight periods can function in territory proclamation, and males are suggested to adjust song output to the level of intruder pressure. We used song playback during the breeding season to simulate intrusions into territories of male Winter Wrens (Troglodytes troglodytes) shortly after dawn. We then compared male singing behaviour during the dawn and dusk chorus before and 1day after the simulated intrusion. One day after the playback, male Wrens increased their song output before sunrise, which confirms our results from a previous study on dawn singing in autumn territories. At dusk, on the evening following the playback, males slightly increased song output after sunset, but singing activity at dusk was generally very low. We found no significant changes of song output after sunrise, before sunset, and between 2days of control without playback. These results are consistent with the hypothesis that dawn and dusk singing is important for territory defence in spring. Unlike in autumn, however, increased singing in spring at dawn and dusk could also serve to defend other resources such as fertile mates or to strengthen the pair bond after a territorial challenge. In comparison with the results on autumnal singing, male Wrens started singing earlier at dawn during the breeding season, and they generally sang more songs at dawn and immediately after playback. The increase in absolute numbers of songs sung in the morning after playback seemed greater in spring than in autumn; however, the proportional increase relative to overall song output was similar in both season

Why and how we should join the shift from significance testing to estimation

A paradigm shift away from null hypothesis significance testing seems in progress. Based on simulations, we illustrate some of the underlying motivations. First, p‐values vary strongly from study to study, hence dichotomous inference using significance thresholds is usually unjustified. Second, ‘statistically significant’ results have overestimated effect sizes, a bias declining with increasing statistical power. Third, ‘statistically non‐significant’ results have underestimated effect sizes, and this bias gets stronger with higher statistical power. Fourth, the tested statistical hypotheses usually lack biological justification and are often uninformative. Despite these problems, a screen of 48 papers from the 2020 volume of the Journal of Evolutionary Biology exemplifies that significance testing is still used almost universally in evolutionary biology. All screened studies tested default null hypotheses of zero effect with the default significance threshold of p = 0.05, none presented a pre‐specified alternative hypothesis, pre‐study power calculation and the probability of ‘false negatives’ (beta error rate). The results sections of the papers presented 49 significance tests on average (median 23, range 0–390). Of 41 studies that contained verbal descriptions of a ‘statistically non‐significant’ result, 26 (63%) falsely claimed the absence of an effect. We conclude that studies in ecology and evolutionary biology are mostly exploratory and descriptive. We should thus shift from claiming to ‘test’ specific hypotheses statistically to describing and discussing many hypotheses (possible true effect sizes) that are most compatible with our data, given our statistical model. We already have the means for doing so, because we routinely present compatibility (‘confidence’) intervals covering these hypotheses

Spiders (Arachnida, Araneae) in winter : differences in the appearance of species in small-scale spaces as a response to daily temperature fluctuations

Pitfall traps were positioned for the investigation of the spider fauna at the northern and southern slopes of three mountain ridges (Chilchberg, Riedberg, and Buechenberg, municipalities Nunningen and Zullwil, canton Solothurn, Switzerland) within the Swiss Jura Mountains. The temperature in the upper litter was measured at three hour intervals. Independent of the weather more or less clear differences between northern and southern slopes could be observed. Maximum day temperature fluctuations of 15.8 °C were measured. There were no significant differences in spider communities based on quantitative comparison methods. However, a qualitative analysis showed major differences in species composition. More than 50% of all species per investigation area showed clear preferences for the northern or the southern slope, with more then two thirds of the individuals only found on either the north or south slopes

Singing activity and spatial behaviour as sexually selected traits in the nightingale "Luscinia megarhynchos"

I examined singing activity and spatial behaviour of male nightingales with regard to possible functions in mate attraction, territory defence, and sperm competition. Male nightingales sang at night before pair formation. They stopped nocturnal song upon pairing, but resumed it if their mate deserted. In contrast, unmated males sang nocturnal song throughout the breeding season. These findings suggest that nocturnal song plays a role in mate attraction. Diurnal singing activity was highest in the hour before sunrise. This pattern was consistent throughout the breeding cycle and was hardly influenced by mating status, indicating that mate attraction is not the main function of the “dawn chorus” in the nightingale. I tested the alternative hypothesis that territorial males sing at dawn to defend their territory against non-territorial males: I translocated unpaired males to the study site (the „Petite Camargue Alsacienne“) and found that the radio-tagged males made extensive excursions visiting several singing males at dawn, but after dawn remained stationary outside occupied territories. These results suggest that non-territorial males use the dawn chorus to assess singing residents or territory occupancy. It also appears that dawn singing of territorial males is important to announce territory occupancy to non-territorial males and thus to defend the territory. In contrast to the hour before sunrise, singing activity later in morning was strongly influenced by the reproductive state of females and peaked during the egg-laying period. This elevated singing activity may not serve primarily to repel cuckolder males pursuing extrapair copulations, since during the morning hours when egg-laying takes place, copulations are thought to less likely result in fertilization than in the days before egg-laying. Accordingly, male nightingales showed the greatest distances to their mates in the morning hours during the egglaying period. Furthermore, extrapair fertilization may not play a major role in influencing singing and spatial behaviour in the nightingale: the rate of extrapair fertilization was relatively low (7.5% of the young as indicated by microsatellite genotyping), and males showed no distinct mate guarding activity. In contrast, the probability for a male to stay unpaired was, on average, 33% per year. I suggest that the high singing activity as well as frequent extra-territorial excursions of males after the fertile period of females serve to maintain the own territory and to gather information on other territories and territory occupancy. This information may be vital for defending a good territory and attracting a mate in the current and subsequent breeding seasons. As only unpaired males sing regularly at night, the proportion of unpaired males can be assessed by comparing the number of nocturnally and diurnally singing males. In an extended study area of 18 km2, I found that about half of 200 – 240 singing males were unpaired. The male-biased adult sex ratio thus may be a general pattern and play an important role in sexual selection of singing activity and spatial behaviour in the nightingale

Vocal interactions in common nightingales ( Luscinia megarhynchos ): males take it easy after pairing

Seasonal patterns of bird song have been studied intensively with a focus on individual males. However, little is known about seasonal patterns of singing during vocal interactions between males. Vocal interactions have been shown to be important in sexual selection as males may signal aspects of motivation or quality. Here, we investigated in nightingales (Luscinia megarhynchos) whether a male's behaviour in vocal interactions at different stages of the breeding season is influenced by its mating status. We examined how males that differ in their subsequent mating success respond to a non-interactive, nocturnal playback presented during the period of mate attraction and subsequently during the egg-laying period. We found that mated males overlapped fewer songs and had a lower song rate during the egg-laying period compared to their responses during the mate-attraction period, whereas unpaired males did not vary in their responses between the two periods. Our results suggest that mating status is a key factor affecting singing behaviour in vocal interactions and that a time-specific singing pattern like song overlapping is used flexibly during vocal interactions. Because song overlapping is thought to be a signal of aggression in male-male vocal interactions, it seems that males vary the level of aggression in vocal interactions according to their mating status and to the stage in the breeding seaso

Effects of territorial intrusions on eavesdropping neighbors: communication networks in nightingales

Animal communication often occurs in communication networks in which multiple signalers and receivers are within signaling range of each other. In such networks, individuals can obtain information on the quality and motivation of territorial neighbors by eavesdropping on their signaling interactions. In songbirds, extracting information from interactions involving neighbors is thought to be an important factor in the evolution of strategies of territory defense. In a playback experiment with radio-tagged nightingales Luscinia megarhynchos we here demonstrate that territorial males use their familiar neighbors' performance in a vocal interaction with an unfamiliar intruder as a standard for their own response. Males were attracted by a vocal interaction between their neighbor and a simulated stranger and intruded into the neighbor's territory. The more intensely the neighbor had interacted with playback, the earlier the intrusions were made, indicating that males eavesdropped on the vocal contest involving a neighbor. However, males never intruded when we had simulated by a second playback that the intruder had retreated and sang outside the neighbor's territory. These results suggest that territorial males use their neighbors' singing behavior as an early warning system when territorial integrity is threatened. Simultaneous responses by neighboring males towards unfamiliar rivals are likely to be beneficial to the individuals in maintaining territorial integrit

Reproductive strategy and singing activity: blue tit and great tit compared

The costs and benefits of bird song are likely to vary among species, and different singing patterns may reflect differences in reproductive strategies. We compared temporal patterns of singing activity in two songbird species, the blue tit (Cyanistes caeruleus) and the great tit (Parus major). The two species live side by side year round, and they have similar breeding ecology and similar rates of extra-pair paternity. However, they differ in two aspects of reproductive strategy that may have an influence on song output: blue tits are facultatively polygynous and have a fairly short breeding season with almost no second broods, whereas great tits are socially monogamous but more commonly raise second broods. We found that great tit males continued singing at high levels during the egg-laying and incubation periods, while monogamously paired blue tit males strongly reduced singing activity after the first days of egg-laying by their female. Since males of both species sang much more intensely shortly before sunrise than after sunrise, at midday or in the evening, this difference was most conspicuous at dawn. No differences in singing activity were found within species when testing for male age. We suggest that in contrast to blue tits, great tit males continued singing after egg-laying to defend the territory and to encourage the female for a possible second broo