Winter thriving : On the role of a boreal city on bird communities

Publisher Copyright: © 2022 The Author(s). Published by Oxford University Press.Information on how urban areas affect bird communities during winter in the boreal region is still scarce. With the aim of assessing such role of the urban habitats on over-wintering boreal birds, I focused on a city-wide approach in the city of Lahti (southern Finland) and two nearby forests (as controls). Point count surveys were conducted in 157 sites within the city and 30 in the control forests. In order to achieve comparable sets of data to contrast with the reference forests, I randomly selected five 30 point count sub-samples from the Lahti city-wide survey. Species richness was, in general, higher in the sub-samples from the city of Lahti. Such pattern did not show relationship with the built cover of the studied sites. Bird abundances were 3.3-5.9 times higher in the urban sub-samples when contrasted with the forest ones. Although results of this study are limited to a single city and consider one wintering season, they clearly illustrate the important role of urban systems as habitat for wintering birds in boreal systems.Peer reviewe

Ant social foraging strategies along a Neotropical gradient of urbanization

During the last decades, urbanization has been highlighted as one of the main causes of biodiversity loss worldwide. Among organisms commonly associated with urban environments, ants occupy urbanized green areas and can live both inside and around human settlements. However, despite the increasing number of studies on the ecological dynamics of ant species developed mainly in temperate urban ecosystems, there is still little knowledge about the behavioral strategies that allow ant species to live and even thrive within cities. In this study, we evaluated the role of urbanization in shaping ant communities, including their social foraging, considering built cover as a gradually changing variable that describes an urban gradient. Specifically, we assessed whether species richness, composition, and the proportion of exotic ant species are related to an urban gradient in a medium-sized Neotropical city immersed in a cloud forest context in Mexico. Moreover, we evaluated the social foraging strategies that could promote ant species coexistence in an urban environment. In general, and contrary to our hypothesis, we found no evidence that the built cover gradient affected the richness, composition, or proportion of exotic ant species foraging on food resources, indicating a filtering and simplification of ant communities given by urbanization. Moreover, we show for the first time that urban ant species exhibited a "discovery-defense strategy", whereby the ant species with the greatest capacity to discover new food resources were those that showed the greatest ability to monopolize it after 120 min of observation, regardless of the type of resource (i.e., tuna or honey bait). Our findings have a direct impact on the knowledge about how urbanization shapes ant communities and behavior, by showing the foraging strategies of ant species that feed on similar food resources present that allows them to coexist in urban environments.Peer reviewe

Neotropical bird communities in a human-modified landscape recently affected by two major hurricanes

Agriculture affects biodiversity on a global scale and especially in the Neotropics, leading to land-management challenges in which native wildlife is forced to interact with high-contrast landscape matrices. Further, the direct and indirect effects of hurricanes impacting native habitat in human-modified landscapes increases reliance on agricultural areas and high-contrast matrices. To understand how avian communities in a human-modified landscape respond to hurricane disturbance, we evaluated post-hurricane trends in species richness, density, structure, and functional and taxonomic composition in avian communities at tropical dry forest and in three agricultural habitats using point-count surveys. We compared our results to a similar study that took place years before the hurricanes in the study area. Similar to pre-hurricane trends, tropical dry forest provided key habitat for endemic species relative to agricultural areas, and tree orchards continued to serve as key secondary habitat for a high species richness and community evenness. However, tree orchards, along with cattle pastures and crop fields, failed to serve as successful buffers of hurricane disturbance by supporting half the estimated bird density of tropical dry forest. Cattle pasture and crop fields were both relatively species poor and had low community evenness compared to tropical dry forest and tree orchards after the hurricanes. Tropical dry forest had distinct species and feeding guild compositions compared to the agricultural habitats. All habitat types after the hurricanes had higher numbers of granivores and a reduction of carnivores compared to pre-hurricane levels. Land management in the study landscape needs to incorporate strategies that raise the hurricane resilience of agricultural areas while providing resources to support higher species richness and density in agricultural systems. Such strategies include the preservation of native trees and shrubs and allowing for the natural succession of habitat in unused areas in tree orchards, cattle pasture, and crop fields.Peer reviewe

A global synthesis of the impacts of urbanization on bird dawn choruses

Urbanization drives changes in acoustic communication systems in some animal species. Noise and light pollution are among the main urban factors known to disrupt the timing and structure of avian singing behaviour. Despite our understanding of the ways in which urbanization can drive variations in avian acoustic communication, our ability to generalize the underlying causes of such variation and its consequences is still limited. Here, we reviewed the literature focused on the study of avian dawn choruses in urban settings at a global scale. Our findings reveal that avian dawn chorus research has focused on the impact of anthropogenic noise on dawn chorus traits (i.e. timing, peak, song output, song frequencies); relationships between light pollution and chorus timing; the effects of temperature, cloudiness, moonlight and natural light on chorus timing; relationships between nocturnal noise and light, and dawn chorus timing; the effects of chemical pollution and supplementary feeding on dawn chorus activity; and ecological patterns of dawn choruses in soundscapes across urban-non-urban gradients. We identified important knowledge gaps in the study of avian dawn choruses in urban settings and thus suggest future research directions, including frameworks (e.g. the urbanization intensity gradient) and consideration of a wider array of urban conditions and variables. Given the complexity of urban settings, we encourage further studies to address the role that all sources of pollution can have on avian acoustic communication at dawn. Additionally, a central question to resolve is whether the function of avian dawn choruses in urban areas differs, and if so how, from non-urban counterparts. Given that most research has been performed across Holarctic cities and towns, studies from tropical and subtropical regions are needed if we aim to understand the phenomenon globally. Finally, studies at the community- and soundscape-level across cities could advance understanding of the way in which urban birds use the acoustic space during the most critical singing time period, dawn.Peer reviewe

Keys to the city : an integrative conceptual framework on avian urban filtering

Publisher Copyright: © 2022 The Author(s). Published by Oxford University Press.Urbanization represents a multi-dimensional ecological 'filter' for birds determined by a myriad of variables that can change over time. Birds colonising an urban system or staying in a habitat that has been recently urbanised need to overcome both the extrinsic (e.g. food predictability, human activities, and inter-specific interaction) and intrinsic filter variables, ranging from genetic to behavioural changes and/or adjustments. An increasing body of knowledge has identified the behavioural component as crucial for individuals facing the spatiotemporal dynamic urban filters, often after other traits and mechanisms have played their role. Through both developmental (i.e. variability in the expression of genes during ontogeny) and activation plasticity (i.e. alteration of behaviour as a result of individual experience), studies have shown that the identification of cues in novel systems - often determined by extrinsic factors - and learning processes, among other factors, have important impacts on decision-making and innovation. The latter are crucial behavioural traits for thriving in urban settings. Thus, we propose an integrative mechanistic framework based on the process experienced by birds who reach a city and manage to persist in the novel system (becoming urban 'utilisers') or those that dwell in an urbanised region who increase their fitness through behavioural responses and adaptations, leading to population persistence (becoming 'dwellers'). Future field research efforts ought not only to widen the range of focal species, regions, and temporal scales of studies, but also to assess behavioural responses in highly urbanised settings, given that much of our knowledge comes from studies performed in urban greenspaces. Additionally, experimental studies are needed to complement the evidence from field research and to determine causal links.Non peer reviewe

The queen of the island : On the density and distribution of the Eurasian Collared-Dove (Streptopelia decaocto) in Cozumel

The Eurasian Collared-Dove (Streptopelia decaocto) is one of the most successful invasive bird species across the world. Worryingly, the invasive dove is a known reservoir of many diseases, some of which can potentially infect mammals (including human beings). Additionally, aggressive behaviors have been recorded toward other bird species resulting in territory and nest usurpation. Thus, the presence of this species poses an important risk for native species with similar habits, particularly in insular systems. Based on this, we carried out this study to assess the density and distribution of the Eurasian Collared-Dove in the island of Cozumel, as well as to evaluate the relationship between their abundance and the environmental characteristics of the places they inhabit. We estimated their distance-corrected densities in the island's largest town and performed an inverse distance weighting (IDW) interpolation to visualize their distribution. We performed a generalized linear model (GLM) to assess relationships between the environmental variables and the abundance of doves using a reduced model procedure. We obtained 137 records of doves present in 94% of all survey sites and an estimated density of 6.8 ind/ha, for a total of 6,670 doves in San Miguel de Cozumel. We did not find a spatial pattern of the dove's distribution on the urban setting, but we found an interaction between their abundances with tree cover and building height. Our findings, together with previous evidence of infection risk and aggressive behavior, make this species a threat to the native species communities of fragile ecosystems such as the island of Cozumel.Peer reviewe

Say what? : On the transmission of acoustic signals in a Neotropical green city

Cities do not only represent noisy systems, but also limit acoustic communication given the complex array of artificial structures through which signals can be trapped or obscured. In this study we performed a field experiment to evaluate the loss of energy of a standardized acoustic emission (generated with notes and a call of the Clay-colored Thrush - Turdus grayi). For this, we emitted the acoustic signal and recovered it at increasing radial distances from 26 fixed emission points (i.e., 10 m, 20 m, 40 m, 80 m, 120 m, 160 m) located across the city of Xalapa (Mexico). Our results show that the emitted signal was not recorded beyond 80 m from the emission point. The number and height of the assessed physical obstacles between the emitted signal and the receiving equipment showed to drive our main result, with built elements representing a major barrier than vegetation ones in terms of the recovered energy of the emitted signal. Interestingly, we found that, for both types of physical obstacles, a height of similar to 7 m was a common threshold influencing the recovered energy of the emitted signal.Peer reviewe

Too hot to handle? On the cooling capacity of urban green spaces in a Neotropical Mexican city

Urban areas are particularly vulnerable to climate change due to the Urban Heat Island (UHI) effect, which can be mitigated by urban vegetation through shading and evapotranspiration. Nevertheless, there is still a lack of spatially explicit information on the cooling capacity of green infrastructure for most Latin American cities. In this study, we employed Land Surface Temperature (LST) of the Neotropical Mexican city of Xalapa to (1) analyze its Surface UHI (SUHI) compared to its peri and extra-urban areas, (2) to assess the cooling capacity of urban green spaces larger than 1ha, and (3) to evaluate the role of green spaces’ size, shape and their surrounding tree cover percentage (Tc) on green spaces cooling range. We evaluated the cooling range of green spaces and their relationships with green spaces metrics and Tc via a linear mixed-effect model and identify threshold values for the variables at 25, 50, 100, and 200m from the borders of green spaces through Classification and Regression Trees. Xalapa exhibits a SUHI of 1.70 °C compared to its peri-urban area and 4.95 °C to the extra-urban area. Green spaces > 2ha mitigated heat at ~2 °C and the cooling range was influenced by the size of green spaces ≥ 2.8ha and Tc > 21% at 50m and only by Tc surrounding the green spaces at 100m and 200m. This shows that the size threshold of urban green spaces should be complemented with the presence of Tc starting at least 50m to maximize the cooling capacity provided by the green infrastructure. Planning agendas should account for the interaction between the size of green spaces and the cumulative cooling effect of scattered vegetation inside urban areas towards compact green cities to cope with urban warming.Peer reviewe

The Effect of Landscape History on the Urban Environment: Past Landscapes, Present Patterns

Peer reviewe

Tree diversity and composition in Mexican traditional smallholder cocoa agroforestry systems

The cultivation of cocoa is a commodity of great importance worldwide. In Mexico, cocoa is grown in Tabasco and Chiapas states in agroforestry systems since pre-Hispanic times, where cocoa is grown under the canopy of shade trees. Crops such as sugarcane and extensive livestock production have gradually reduced the area devoted to cocoa cultivation in the region. Yet, farmers keep small portions of the cocoa agroforestry systems to maintain the local floristic diversity. This practice seems to be a successful contribution to plant conservation. To determine the management practices used by farmers in the agroforestry cocoa systems and the diversity of products they harvest, a non-probabilistic sampling was carried out in 38 shade cocoa plots of 20 x 50 m each (19 in Tabasco and 19 in Chiapas). We counted and identified all trees with DBH >= 5 cm, recording their height. We estimated canopy cover at 20 points within each plot. Our results show no tree species richness differences between states, but there were differences at the municipality level; Pichucalco (Chiapas) had the highest tree species richness. Considering all tree species, there was a higher tree density in Tabasco than in Chiapas. Regarding only cocoa trees, there was also a higher abundance in Tabasco than in Chiapas. In both cases, farmers obtain a wide variety of products for self-consumption and local market sale from their cocoa agroforestry systems (e.g., timber, fruit, and grains). The wide floristic diversity in these agroecosystems aids native plant species conservation and could favor the increase of agroforestry plantations associated with cocoa cultivation.Peer reviewe