Birds, Volume 3, Issue 3 (September 2022) – 6 articles

The context and outcome of aggressive interactions between individuals has important fitness consequences. Displacements—an aggressive interaction wherein one individual is chased from a location by another—also have implications for social hierarchy formation and geographic distribution in songbirds. Morphological correlates, like body size, and social correlates, such as dominance rank, have been shown to mediate displacements in songbirds. However, the role of the physical environment, namely temperature, humidity, and time of day, which may influence an individual’s energy needs and thus displacement motivation, has remained understudied. We monitored songbird feeding and displacement behaviors using computerized automated feeders. We observed asymmetric differences across species in displacement involvement. To identify the conditions of the social and physical environment that are associated with the occurrence and outcome of songbird displacements at supplemental feeders, we use the machine learning approach, random forest, which is a novel method to the fields of ornithology and animal behavior. From our random forest models, we found that the attributes of the physical environment (i.e., humidity and the time of day) are associated with the occurrence of a displacement event, whereas the attributes of the social environment (i.e., species of the displacer and displaced individuals) are associated with which species are involved. These results provide context to develop further observational and experimental hypotheses to tease apart the inner workings of these multifactorial behaviors on a larger scale and provide a proof of concept for our analytical methods in the study of avian behavior. Full article

Understanding the migratory route of raptors in their breeding and wintering grounds is crucial for ensuring their effective conservation. This study presents the preliminary findings through satellite telemetry to describe the summer and winter home ranges, movement ecology, activity, and migration routes of single individuals of Greater Spotted Eagle (Clanga clanga), Indian Spotted Eagle (Clanga hastata), Tawny Eagle (Aquila rapax), and Pallid Harrier (Circus macrourus). We calculated the home ranges as the minimum convex polygons (MCPs) and kernel utilisation distributions (KUD). Pallid Harrier had the smallest home range size of 4.29 km² (95% MCP) and 3.98 km² (95% KUD) in its breeding ground located in Russia, while the Greater Spotted Eagle had the largest home range size of 9331.71 km² (95% MCP) and 5991.15 km² (95% KUD) in Kazakhstan. The monthly and daily distances covered by tagged birds were significantly higher during migration. Our study also reports the first record of the winter and summer home range of the Indian Spotted Eagle in Pakistan. The tagged raptor used low elevation flyways than the straighter northern flyways over the Himalayan Mountain range, as found in another earlier study. Our study is the foremost satellite telemetry attempt from the region, highlighting important aspects of the migration route of migratory raptors to India. Full article

Grey-faced Petrels (Pterodroma gouldi) are colonial burrowing seabirds predominantly nesting on offshore islands of the upper North Island of New Zealand. We studied their chick provisioning on Te Hāwere-a-Maki during two years of unfavourable warmer La Niña conditions in 2011 and 2013. We intensively monitored chicks in each year, weighing chicks every 12 h for 10 consecutive days to estimate meal sizes following chick provisioning and to estimate 12-hourly body mass loss as a function of time since last feeding. We found a quadratic relationship of body mass loss with time since last feeding, with rapid digestion of meals following provisioning followed by a period of fasting from five days post feeding as chicks waited an unknown and variable amount of time until their next meal. The rate of body mass loss did not depend on chick age nor body mass, and did not differ between years, but heavier chicks included in our study were more likely to successfully fledge, suggesting a legacy of adult provisioning prior to our study commencing. Our regular handling of chicks for monitoring has no discernible impact on parent provisioning compared to a set of control chicks. The mean estimates of 100-gram meal sizes and 10-day foraging trip durations are likely to be below the break-even point for this species. Full article

Invasive exotic species are currently a topic of interest for environmental management agencies and the media. This is due to the socio-economic and environmental problems that they are causing or may cause. The Monk Parakeet is a clear example of this, especially in some large cities, where populations are growing quickly, and their distribution continues to expand. In our study, we focused on a population that has been closely monitored during the last 25 years to understand its growth and change on a local scale to determine the maximum sustainable population size in the invaded area and to check when this population began to act as a source of new breeding colonies to adjacent areas. The first breeding of the species occurred in 2002, and from then, the average growth rate (r) of the population was 0.191 until 2016, when it stabilized and declined slightly (r = −0.043). The maximum growth rate occurred during the years 2002 and 2007 and was 0.314. The results obtained give us information about the carrying capacity of the study area, allowing us to explain the dispersal process of the species to neighbouring areas, with populations that have reached maximum size serving as sources of individuals dispersing to suitable areas. In our study area, the species shows a strong preference for building its nests in palm trees and electric utility structures. Our study’s local focus on studying the population dynamics of an invasive species may allow us to understand the increased range of the species on a larger scale, which is necessary in order to be able to design appropriate and effective management strategies. Full article

Each year, billions of seabirds undertake migrations, connecting remote regions of the world, potentially synchronizing population fluctuations among distant areas. This connectedness has implications for the uncertainty calculations of the total seabird bycatch estimate at a regional/global scale. Globally, fisheries bycatch poses a major problem in fishery management, and estimating the uncertainty associated with a regional/global seabird bycatch estimate is important because it characterizes the accuracy and reliability of the fisheries’ impact on the seabird populations. In this study, we evaluate different assumptions underlying the estimation of the variability of the total seabird bycatch at a regional/global scale based on local assessment reports. In addition to theoretical analysis, we also simulate multiple spatially distant separately managed areas with relatively low levels of observer coverage, based on bycatch data from the Western and Central Pacific Fisheries Commission convention area. The results show that assuming a completely synchronized variation produced the most conservative uncertainty estimate and it also missed an opportunity to improve the precision. Simplified correlation structures also failed to capture the complex dynamics of bycatch rates among spatially distant areas. It is recommended to empirically estimate the correlation of bycatch rates between each pair of sources based on bycatch rate time series. Full article

The visual perception of birds is an incredibly exciting subject of research. Birds have significantly higher visual acuity than most other animals, which helps them stay safe in flight and detect their prey. Understanding how the eyes send information to the brain for additional processing is crucial. The brain has sections (nuclei) that accept input from the retina. The key areas where information is processed are the hyperpallium apicale (HA), hippocampus (HP), optic tectum (TeO), nucleus rotundus (RoT), and the geniculatus lateralis ventralis (Glv); among these, the RoT is one of the most investigated nuclei for vision. This study looked at how the visual centers of non-photoperiodic songbirds (Spotted Munia) adapt in different life history stages by looking at NPY expression. We immunohistochemically quantified NPY expression in four different seasons, including pre-breeding (June), breeding (September), post-breeding (December), and regressed (March) in the brain of Spotted Munia. We evaluated changes in the expression levels of the peptide throughout the year, by determining the expression at four different periods throughout the year. Peptide expression levels were projected to fluctuate within photoperiod-induced seasons. It was discovered that the parts of the brain related to vision (RoT, HA, and HP) have a higher number of immunoreactive cells during their mating season, i.e., during the summer. The appearance of NPY, a non-photic marker, in brain areas linked with light perception, was fascinating. Indirectly, NPY aids avian reproduction in a variety of ways. These findings demonstrate the importance of these nuclei in the process of reproduction, as well as the involvement of NPY in the visual brain areas of Spotted Munia. Full article