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Habitat loss represent a major threat to biodiversity, however, the modulation of their effects by the non-habitat matrix surrounding habitat patches is still undervalued. The landscape matrix might change community assembly in different ways. For example, low-quality matrices can accentuate environmental filtering by reducing resource availability and/or deteriorating abiotic conditions but they may also over limit dispersal of organisms and make communities more prone to ecological drift. To understand how matrix quality modulates the effects of habitat loss, we quantified the relative importance of environmental filter and ecological drift in bird occurrences across more local (400 m buffer around sampling sites) and broader (2 km focal landscapes) gradients of habitat loss embedded in low- and high-quality matrices. We used a trait-based approach to understand habitat loss filtering effects on forest specialist and habitat generalist bird occurrences. We found that low-quality matrices, composed mainly of low-productive pasturelands, increased the severity of habitat loss filtering effects for forest specialist birds, but only at the landscape scale. Bird occurrence was in general higher in high-quality matrices, i.e., more heterogeneous and with low-contrasting edges, indicating the role of the matrix quality on attenuating species extinction risks at the landscape scale probably due to mass effect. Moreover, forest specialists presented a strong negative response to habitat loss filtering across different functional traits, while generalists presented a high variability in traits response to habitat loss. We raised evidence in supporting that landscape habitat loss filtering may be relaxed or reinforced depending on the quality of the matrix, evidencing that matrix quality has a strong impact in modulating community assembly processes in fragmented landscapes. In practical terms, it means that improving matrix quality may help in maintaining the high diversity of birds even without any increase in native forest cover.

To mitigate the shortage of natural breeding sites in cities, nest-boxes are provided for cavity-nesters. However, these are not the breeding sites these animals originally evolved in and optimised their breeding performance to. It thus remains inconclusive if nest-boxes can provide adequate substitutes, ensuring equivalent fitness returns for breeding animals. Additionally, the majority of knowledge on the ecology of urban birds comes from nest-box populations, but no study to date directly compared fitness consequences of breeding inside nest-boxes in relation to natural-cavities in an urban context. This limits our understanding of the urban ecology of cavity-nesters and addressing its functional meaning. We investigate fitness consequences and life-history trait variation according to the nesting site type to provide a comprehensive understanding of conservation potential of nest-boxes in cities and to support/question generalisations stemming from nest-box studies on urbanization. We directly compare the reproductive performance of two small passerines, blue tits and great tits, breeding in nest-boxes as opposed to natural-cavities in a seminatural forest of a capital city using a quasi-experimental setting. We show that the effects of nest type vary between species: in blue tits, fitness proxies were negatively affected by nest-boxes (lower fledging success and fledgling numbers, longer time spent in nest and later fledging date in comparison to natural-cavities), while great tit performance appeared to be unaffected by nest type. We detected that both species breeding in nest-boxes accelerated incubation onset, but since there were no major differences in pre-hatching traits (lay date, clutch size, hatching rates) between the nest types, we attribute the fitness deterioration to post-hatching effects. Interestingly, overall breeding density of tits in urban natural-cavities was higher than observed in a primeval habitat. Nest-boxes may become an ecological trap for some species and the unaffected species can consequently outcompete them, decreasing overall biodiversity in cities. We highlight the ecological importance of old-growth tree stands, providing natural tree cavities for city-breeding animals. Due to the detected nest type-dependent variation in reproductive performance, we support the criticism regarding the unconditional extrapolation of evolutionary and ecological interpretations of nest-box studies to general populations.

A major barrier to advancing ornithology is the systemic exclusion of professionals from the Global South. A recent special feature, Advances in Neotropical Ornithology, and a shortfalls analysis therein, unintentionally followed a long-standing pattern of highlighting individuals, knowledge, and views from the Global North, while largely omitting the perspectives of people based within the Neotropics. Here, we review current strengths and opportunities in the practice of Neotropical ornithology. Further, we discuss problems with assessing the state of Neotropical ornithology through a northern lens, including discovery narratives, incomplete (and biased) understanding of history and advances, and the promotion of agendas that, while currently popular in the north, may not fit the needs and realities of Neotropical research. We argue that future advances in Neotropical ornithology will critically depend on identifying and addressing the systemic barriers that hold back ornithologists who live and work in the Neotropics: unreliable and limited funding, exclusion from international research leadership, restricted dissemination of knowledge (e.g., through language hegemony and citation bias), and logistical barriers. Moving forward, we must examine and acknowledge the colonial roots of our discipline, and explicitly promote anti-colonial agendas for research, training, and conservation. We invite our colleagues within and beyond the Neotropics to join us in creating new models of governance that establish research priorities with vigorous participation of ornithologists and communities within the Neotropical region. To include a diversity of perspectives, we must systemically address discrimination and bias rooted in the socioeconomic class system, anti-Blackness, anti-Brownness, anti-Indigeneity, misogyny, homophobia, tokenism, and ableism. Instead of seeking individual excellence and rewarding top-down leadership, institutions in the North and South can promote collective leadership. In adopting these approaches, we, ornithologists, will join a community of researchers across academia building new paradigms that can reconcile our relationships and transform science. Spanish and Portuguese translations are available in the Supplementary Material.

Animals breeding in anthropogenic shelters such as nest-boxes experience nesting environment in which they did not originally evolve. Over the past decades, they are additionally challenged by climate change – a major environmental force influencing their reproductive ecology. Despite the central importance of nesting microclimate for offspring development and fitness, very little is known about the thermal properties of human-provided nests compared to natural ones. While it has been demonstrated that artificial nests provide poorer thermal insulation in comparison to natural breeding sites, there is no evidence on how these shifts are shaped along the reproductive stages. In particular, comparisons focusing on the time when offspring are in the nest are lacking. Here, we compare the microclimatic conditions (temperature and absolute humidity) along the nesting cycle (from nest-site choice in early spring until post-fledging) in natural cavities and nest-boxes used by several species of hollow-nesting passerines in a temperate deciduous forest. We confirm that across all nesting stages, nest-boxes are thermally unstable when compared to natural cavities, with higher temperature maximums, larger amplitudes and worse insulation from maximum ambient temperatures relative to natural cavities. Importantly, in the presence of young, and after they start to thermoregulate on their own, nest-boxes are also more humid than natural cavities. Artificial nest microclimate is likely to amplify the adverse effects of projected temperature increases modelled under climate change scenarios, specifically by compromising thermoregulation and increasing water requirements of developing animals. In contrast, internal microclimatic shifts were mitigated in natural cavities 3.0 times more effectively than in nest-boxes when offspring were in the nest (in terms of mean daily differences from ambient temperature). We stress that conservation efforts should focus on the protection of habitats offering natural breeding-hollows to reduce climate change impacts on breeding animals.

In most vertebrates, males are larger than females. For raptors, sexual size dimorphism is reversed, with females being larger. Reversed sexual dimorphism (RSD) in raptors is strongly linked to diet, with species feeding on the most agile prey, for example bird-eating raptors, showing the greatest size differences between the sexes. Hypotheses for reversed sexual dimorphism (RSD) include the ‘intersexual competition’ hypothesis, which proposes that RSD evolved to enable pairs to expand their dietary niche (taking a wider range of prey sizes) during the nestling period when both sexes occupy and hunt within the same territory, and thereby reduce competition between the sexes. If intersexual competition is responsible for the evolution of RSD, we predict that sex-related differences in prey size and dietary niche breadth will be particularly pronounced during the nestling period (cf. the non-nestling period). We explore this prediction in the highly dimorphic Eurasian Sparrowhawk (Accipiter nisus), which displays the largest degree of RSD of all raptors, using web-sourced photographs to identify diet throughout the entire year. We analysed 666 photographs of sparrowhawks on their prey over time. In contrast to our predictions, sex-specific prey sizes were most similar during the nestling period compared to any other time of the year. Both males and females reduced the size of their prey during the nestling period which may be a result of the ‘ingestion rate’ hypothesis, or a strategy employed to prevent hunting-related injuries during this critical period of the year.

1. Environmental conditions during early-life development can have lasting effects on individual quality and fitness. Telomere length (TL) may correlate with early-life conditions and may be an important mediator or biomarker of individual quality or pace-of-life, as periods of increased energy demands can increase telomere attrition due to oxidative stress. Thus, knowledge of the mechanisms that generate variation in TL, and the relation between TL and fitness, is important in understanding the role of telomeres in ecology and life-history evolution. 2. Here, we investigate how environmental conditions and morphological traits are associated with early-life TL and if TL predicts natal dispersal probability or components of fitness in two populations of wild house sparrows (Passer domesticus). 3. We measured morphological traits and blood TL in 2746 nestlings from 20 cohorts (1994-2013) and retrieved data on weather conditions. We monitored population fluctuations, and individual survival and reproductive output using field observations and genetic pedigrees. We then used generalized linear mixed-effects models to test which factors affected TL in early-life, and if TL predicted dispersal propensity, or was associated with recruitment probability, mortality risk, or reproductive success. 4. We found a negative effect of population density on TL, but only in one of the populations. There was a curvilinear association between TL and the maximum daily North Atlantic Oscillation (NAO) index during incubation, suggesting that there are optimal weather conditions that result in the longest TL. Dispersers tended to have shorter telomeres than non-dispersers. TL did not predict survival, but we found a tendency for individuals with short telomeres to have higher annual reproductive success. 5. Our study showed how early-life TL is shaped by effects of growth, weather conditions and population density, supporting that environmental stressors negatively affect TL in wild populations. In addition, TL may be a mediator or biomarker of individual pace-of-life, with higher dispersal rates and annual reproduction tending to be associated with shorter early-life TL in this study. However, clear associations between early-life TL and individual fitness seems difficult to establish and may differ between different populations in the wild.

Morphological variation among individuals has the potential to influence multiple life history characteristics such as dispersal, migration, reproductive success, and survival (Wilder et al. 2016). Individuals that are in better “condition” can disperse or migrate further or more successfully, have greater reproductive success, and survive longer (Heidinger et al. 2010; Liao et al. 2011; Wilder et al. 2016), particularly in years where environmental conditions are harsh (Milenkaya et al. 2015). Body condition is defined in various ways, but is most often measured using an individual’s energetic or immune state (Milenkaya et al. 2015). These traits are difficult to measure directly, therefore a variety of morphological proxies to quantify condition are used instead, including fat score (Kaiser 1993), weight, ratio of weight to tarsus length (Labocha et al. 2014), a scaled mass index (Peig and Green 2009), as well as hematological indices for immune system function (Fleskes et al. 2017; Kraft et al. 2019). However, there is mixed support regarding whether these condition indices relate to life history characteristics (Labocha et al. 2014; Wilder et al. 2016), and whether the relationship is linear (McNamara et al. 2005; Milenkaya et al. 2015). Additionally, although some investigations use multiple morphological proxies for condition (e.g. Warnock and Bishop 1998), rarely have there been direct comparisons among proxies to validate that they measure the same trait. In this investigation, we define condition as an energetic state and we attempt to measure it by comparing two indices (fat score and the scaled mass index) to validate whether they measure the same trait and whether they correlate with measures of reproductive success in our study system, the great-tailed grackle (Quiscalus mexicanus). We found that the morphological proxies did not correlate with each other, indicating that they do not measure the same trait. Further, neither proxy correlated with reproductive success in males, measured as whether a male held a territory containing nests or not. We found that females with a high scaled mass index had a significantly lower probability that their nest would survive on any given day. However, there was no relationship between female fat score and nest survival. These results indicate that measures of condition should be validated before relying on their use as a condition proxy in grackles and birds in general. Future research should further investigate our unexpected result that higher scaled mass index correlated with lower nest survival to better understand the importance of energetic condition for reproductive success - a necessary component for selection to act.

When selecting a breeding site, individuals can use social information to reduce the uncertainty regarding habitat quality. In particular, individuals from several bird species tend to reuse nests previously occupied by competitors. Re-occupying nests previously used by conspecifics or heterospecifics could result from exploiting social information by copying competitors’ choice (the ‘social information’ hypothesis). Alternatively, it could allow fulfilling the needs for a comfortable nest substrate (e.g. by improving thermal insulation or reducing egg breakage risks) at low costs, regardless of previous occupancy (the ‘comfort’ hypothesis). Here, we aimed to determine which of these two mechanisms triggered the preference for old conspecific nest material in a secondary cavity-nesting raptor which does not add lining materials to its nest, the lesser kestrel (Falco naumanni). Using an experimental design forcing settling lesser kestrels to choose between two adjacent nestboxes containing different substrates, we detected a strong preference for comfortable substrates (peat moss, or conspecific or European roller old nest material) over uncomfortable mineral substrate, especially when the comfortable substrate also provided social information about previous nest use by a competitor. Despite the apparent absence of preference when directly comparing settlement patterns in comfortable substrates with and without social information, early-settling individuals favoured the substrate with social information, while late-settling ones favoured the substrate without social information. This could reflect intraspecific competition avoidance by late arriving individuals that may be competitively inferior compared to early arriving ones. This hypothesis is supported by a later laying date of young (up to two years old) breeders compared to older ones in our population. Our findings suggest that both comfort seeking and social information use explain preference for previously used nest cavities, and that nest site choices may depend on individual competitive abilities and experience.

Moult is a process, usually occurring annually, in which birds replace their plumage. It is one of the most crucial life-history traits because it restores the functions of plumage and allows a bird to adapt to environmental conditions or special seasonal needs such as breeding and camouflage during non-breeding season. Consequently, moulting has advantages in terms of future performance. However, it also has immediate costs related to producing protein-rich tissue, reduced thermoregulation and flight performance. Expression of such costs may depend on a wide array of physiological and environmental factors experienced by an individual. Considering a variety of factors affecting moult dynamics in single studies, we use a systematic meta-analytical approach to summarise existing evidence and look for general patterns in how moult depends on both extrinsic (environment, ecological variability) and intrinsic (physiology, energy reserves, life stage) factors.

Drones are rapidly becoming part of environmental monitoring and management applications. They provide an opportunity to improve a number of activities related to monitoring population dynamics of aggregations of wildlife. Bird surveys using drones have attracted particular attention, with a range of potential metrics able to be derived from high resolution drone imagery. Whilst a number of papers have shown that drone-based data can be used to effectively and accurately count and monitor features in bird colonies, the use of drone-derived data in real management and monitoring applications remains rare. This is in part due to a lack of clear guidelines as to the capability of drones and how to plan and successfully execute flights, but also due to a lack of information pertaining to specific target species and related contextual and environmental considerations. In this paper we outline a protocol for using drones to assist in the monitoring of colonies of breeding colonial waterbirds. We base the protocol on experience carrying out drone-based surveys of several colonies ranging in population from ~1000 to ~250,000 individuals. These are among the largest colonies ever surveyed via drone. We provide end-to-end guidelines, including detectability, flight planning and execution, on-ground data collection, image processing and target feature counting.

Understanding species-specific relationships with their environment is essential for ecology, biogeography, and conservation biology. Moreover, understanding how these relationships change with spatial scale is critical to mitigating potential threats to biodiversity. But methods which measure inter-specific variation in responses to environmental parameters, generalizable across multiple spatial scales, are lacking. We used broad-scale citizen science data, over a continental scale, integrated with remotely-sensed products, to produce a measure of response to urbanization for a given species at a continental-scale. We then compared these responses to modelled responses to urbanization at a local-scale, based on systematic sampling within a series of small cities. For 49 species which had sufficient data for modelling, we found a significant relationship (R2 = 0.51) between continental-scale urbanness and local-scale urbanness. Our results suggest that continental-scale responses are representative of small-scale responses to urbanization. We also found that relatively few citizen science observations (~250) are necessary for reliable estimates of continental-scale urban scores to predict local-scale response to urbanization. Our method of producing species-specific urban scores is robust and can be generalized to other taxa and other environmental variables with relative ease.

The use of crowdsourced data is growing rapidly, particularly in ornithology. Citizen science greatly contributes to our knowledge, however, little is known about the reliability of data collected in that way. We found, using an online picture quiz, that self-proclaimed expert birders were more likely to misidentify common British bird species as exotic or rare species, compared to people who rated their own expertise more modestly. This finding suggests that records of rare species should always be considered with caution even if the reporters consider themselves to be experts. In general, however, we show that self-rated expertise in bird identification skills is a reliable predictor of correct species identification. Implementing the collection of data on self-rated expertise is easy and low-cost. We therefore suggest it as a useful tool to statistically account for variability in bird identification skills of citizen science participants and to improve the accuracy of identification data collected by citizen science projects. Edited: broken link fixed (12/3/2019)

• Recent advances in drone technology have rapidly led to their use for monitoring and managing wildlife populations but a broad and generalised framework for their application to complex wildlife aggregations is still lacking • We present a generalised semi-automated approach where machine learning can map targets of interest in drone imagery, supported by predictive modelling for estimating wildlife aggregation populations. We demonstrated this application on four large spatially complex breeding waterbird colonies on floodplains, ranging from ~20,000 to ~250,000 birds, providing estimates of bird nests • Our mapping and modelling approach was applicable to all four colonies, without any modification, effectively dealing with variation in nest size, shape, colour and density and considerable background variation (vegetation, water, sand, soil etc.). Our semi-automated approach was between 3 to 8 times faster than manually counting nests from imagery at the same level of accuracy • This approach is a significant improvement for monitoring large and complex aggregations of wildlife, offering an innovative solution for monitoring large and complex aggregations where ground counts are costly, difficult or not possible. Our framework requires minimal technical ability, is open-source (e.g., Google Earth Engine and R), and generalisable to other surveys

Conservation concern for the northern goshawk (Accipiter gentilis) reflects evidence that goshawks may abandon nest sites or suffer from reduced nesting success in response to some forms of timber harvest. However, this evidence is mixed and has yet to be reviewed systemically and quantitatively. Therefore, we conducted a meta-analysis to assess the extent to which timber harvest and tree size explain variation in goshawk productivity and site occupancy. Goshawk productivity was not significantly explained by the presence of nearby timber harvest nor by the average size of nearby trees either in North America or in Eurasia or when averaged across all studies. Effect sizes differed dramatically among studies and the average effect size was close to zero (Zr = 0.04). However, timber harvest and tree size together more strongly explained goshawk occupancy of nest sites or territories. Within studies, goshawk nest sites or territories with less timber harvest nearby or relatively larger trees were, in most cases, more likely to be occupied. When we estimated average effect sizes separately for the two continents, the averages were moderate, consistent (Zr = 0.23–0.27), and significantly > 0. When we combined studies from North America and Eurasia, average effect sizes for timber harvest (Zr = 0.24) and tree size (Zr = 0.25) were similar in strength and both significantly > 0. Thus taken together, our results suggest that although both timber harvest and a lack of large trees are associated with lower occupancy by nesting goshawks, pairs that nest near timber harvest or in small trees have indistinguishable nesting success from pairs nesting in large trees or farther from timber harvest. We found substantial heterogeneity in results among studies, especially within North America, which is not surprising given that studies differed greatly in research methods, forest type, and forest management. In conclusion, our results suggest goshawk nest sites in populations of conservation concern, such as A. g. laingi, may need more protection from timber harvest than they are currently receiving. Equally important, to better understand effects of forest management on goshawks, we recommend additional studies designed to: (1) better identify the spatial and temporal extent of the effect of timber harvest on goshawk site occupancy; and (2) determine what goshawks do and where they go after a timber harvest.