Nests in the cities: adaptive and non-adaptive phenotypic plasticity and convergence in an urban bird

Long-term population trends of 48 urban bird species correspond between urban and rural areas

Colonization of urban areas by wild species is a widespread phenomenon investigated from various ecological and evolutionary perspectives, yet long-term population trends of organisms in urban areas remain understudied. To fill this knowledge gap, we used data from a large-scale breeding bird monitoring scheme and computed population trends in 48 urban bird species in urban and rural areas of a central European country, Czechia. In most species, trends were similar in both environments, indicating common drivers and/or connections between urban and rural populations. In species with significant trends, the positive trends prevailed, suggesting good performance of urbanized species. This may result from wildlife-friendly environmental changes in cities, such as the expansion of green areas and the maturing of woody vegetation. In respect to species traits, more positive trends were found in larger species than in smaller species in both habitats, likely due to the recovery of previously depleted populations.

Urban birds become less fearful following COVID-19 reopenings

Following the COVID-19 pandemic, many people around the world stayed home, drastically altering human activity in cities. This exceptional moment provided researchers the opportunity to test how urban animals respond to human disturbance, in some cases testing fundamental questions on the mechanistic impact of urban behaviours on animal behaviour. However, at the end of this 'anthropause', human activity returned to cities. How might each of these strong shifts affect wildlife in the short and long term? We focused on fear response, a trait essential to tolerating urban life. We measured flight initiation distance-at both individual and population levels-for an urban bird before, during and after the anthropause to examine if birds experienced longer-term changes after a year and a half of lowered human presence. Dark-eyed juncos did not change fear levels during the anthropause, but they became drastically less fearful afterwards. These surprising and counterintuitive findings, made possible by following the behaviour of individuals over time, has led to a novel understanding that fear response can be driven by plasticity, yet not habituation-like processes. The pandemic-caused changes in human activity have shown that there is great complexity in how humans modify a behavioural trait fundamental to urban tolerance in animals.

The singing activity of the Yellowhammer (Emberiza citrinella) under traffic noise around highways

Steadily increasing human population is changing the environment in many ways. One of the most disturbing impacts is the development of anthropogenic noise pollution connected to ever-growing traffic intensity. The road network can have both positive and negative effects on biodiversity and populations. Many bird species use acoustic communication to establish and maintain their territories and for intra-pair and adult–young communication. Noise pollution can impact negatively on breeding success and biorhythm if this communication is masked by noise and the individuals must adjust their singing activity. Yellowhammer (Emberiza citrinella) is a common bird species of agricultural landscapes whose population is declining due to agricultural intensification. It is found also in habitats near highways with forest steppe-like characteristics, where it is affected by the high levels of anthropogenic noise pollution. This study aimed to determine how this species adapts to noise from highway traffic by adjusting its singing activity. The influence of locality type, immediate and long-term impact of traffic noise on the average and total length of song sequences in the birdsong, and influence on the total number of recorded song sequences during the second hour after sunrise were evaluated in this study. Our results showed that Yellowhammer’s singing activity changed in localities close to highways compared to agricultural landscape. With increasing long-term traffic intensity on highways, song duration of the Yellowhammer song was decreasing. The present traffic intensity led to later onset of dawn chorus and decreasing strophe length with increasing number of passing vehicles. Furthermore, in the agricultural landscape, Yellowhammer’s song duration increased with increasing distance from the nearest road.

No evidence of repeated song divergence across multiple urban and non-urban populations of dark-eyed juncos (Junco hyemalis) in Southern California

Urbanization can affect species communication by introducing new selection pressures, such as noise pollution and different environmental transmission properties. These selection pressures can trigger divergence between urban and non-urban populations. Songbirds rely on vocalizations to defend territories and attract mates. Urban songbirds have been shown in some species and some populations to increase the frequencies, reduce the length and change other temporal features of their songs. This study compares songs from four urban and three non-urban populations of dark-eyed juncos (Junco hyemalis) throughout Southern California. We examined song length, trill rate, minimum frequency, maximum frequency, peak frequency and frequency bandwidth. We also compared songs recorded from one urban junco population in San Diego nearly two decades ago with recently collected data in 2018-2020. Over all comparisons, we only found significant differences between UCLA and the 2006/2007 UCSD field seasons in minimum and maximum frequencies. These findings partially support and are partially in contrast to previous urban song studies. As urban areas expand, more opportunities will arise to understand urban song divergence in greater detail.

No evidence of repeated song divergence across multiple urban and non-urban populations of dark-eyed juncos (Junco hyemalis) in Southern California

Urbanization can affect species communication by introducing new selection pressures, such as noise pollution and different environmental transmission properties. These selection pressures can trigger divergence between urban and non-urban populations. Songbirds rely on vocalizations to defend territories and attract mates. Urban songbirds have been shown in some species and some populations to increase the frequencies, reduce the length and change other temporal features of their songs. This study compares songs from four urban and three non-urban populations of dark-eyed juncos (Junco hyemalis) throughout Southern California. We examined song length, trill rate, minimum frequency, maximum frequency, peak frequency and frequency bandwidth. We also compared songs recorded from one urban junco population in San Diego nearly two decades ago with recently collected data in 2018-2020. Over all comparisons, we only found significant differences between UCLA and the 2006/2007 UCSD field seasons in minimum and maximum frequencies. These findings partially support and are partially in contrast to previous urban song studies. As urban areas expand, more opportunities will arise to understand urban song divergence in greater detail.