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  1. Abstract Aim

    Understanding variation in offspring energy expenditure is important because energy is critical for growth and development. Weather may exert proximate effects on offspring energy expenditure, but in altricial species these might be masked by parental care and huddling with siblings. Such effects are particularly important to understand given changing global weather patterns, yet studies of wild offspring in the presence of parental care are lacking. Offspring energy expenditure may also vary among species due to evolved responses to environmental selection pressures, requiring studies at both proximate and ultimate levels.

    Location

    USA, South Africa, Malaysia.

    Time period

    2016–2019.

    Major taxa studied

    Songbirds.

    Methods

    We used the doubly‐labelled water technique to estimate nestling daily energy expenditure of 54 songbird species across three continents. We used Bayesian phylogenetic mixed models to test proximate and evolutionary causes of variation in offspring energy expenditure while accounting for phylogeny and phylogenetic uncertainty.

    Results

    Offspring energy expenditure increased with more rainfall and colder air temperatures, but decreased among offspring in broods with more siblings. Across species, nestling and adult mortality, but not growth rate, were positively associated with offspring energy use.

    Main conclusions

    Weather had clear proximate effects on offspring energy expenditure and parents were either unable or unwilling to fully offset these effects. However, the decrease in offspring energy use when huddling with more siblings demonstrated a modulating effect of life history traits. For example, high nest predation rates favour reduced parental care and can force offspring to spend more energy coping with environmental conditions. Furthermore, reduced energy expenditure is thought to facilitate increased longevity, which is increasingly realized with lower extrinsic mortality rates, providing an explanation for the positive association between adult mortality and offspring energy expenditure. Ultimately, both proximate and evolutionary influences need to be considered to better understand causes of offspring energetics.

     
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  2. Abstract Aim

    Two important environmental hazards for nocturnally migrating birds are artificial light at night (ALAN) and air pollution, with ambient fine particulate matter (PM2.5) considered to be especially harmful. Nocturnally migrating birds are attracted to ALAN during seasonal migration, which could increase exposure to PM2.5. Here, we examine PM2.5concentrations and PM2.5trends and the spatial correlation between ALAN and PM2.5within the geographical ranges of the world’s nocturnally migrating birds.

    Location

    Global.

    Time period

    1998–2018.

    Major taxa studied

    Nocturnally migrating birds.

    Methods

    We intersected a global database of annual mean PM2.5concentrations over a 21‐year period (1998–2018) with the geographical ranges (breeding, non‐breeding and regions of passage) of 225 nocturnally migrating bird species in three migration flyways (Americas,n = 143; Africa–Europe,n = 36; and East Asia–Australia,n = 46). For each species, we estimated PM2.5concentrations and trends and measured the correlation between ALAN and PM2.5, which we summarized by season and flyway.

    Results

    Correlations between ALAN and PM2.5were significantly positive across all seasons and flyways. The East Asia–Australia flyway had the strongest ALAN–PM2.5correlations within regions of passage, the highest PM2.5concentrations across all three seasons and the strongest positive PM2.5trends on the non‐breeding grounds and within regions of passage. The Americas flyway had the strongest negative air pollution trends on the non‐breeding grounds and within regions of passage. The breeding grounds had similarly negative air pollution trends within the three flyways.

    Main conclusions

    The combined threats of ALAN and air pollution are greatest and likely to be increasing within the East Asia–Australia flyway and lowest and likely to be decreasing within the Americas and Africa–Europe flyways. Reversing PM2.5trends in the East Asia–Australia flyway and maintaining negative PM2.5trends in the Americas and Africa–Europe flyways while reducing ALAN levels would likely be beneficial for the nocturnally migrating bird populations in each region.

     
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  3. Abstract Aim

    Anthropogenic noise pollution (ANP) is a globally invasive phenomenon impacting natural systems, but most research has occurred at local scales with few species. We investigated continental‐scale breeding season associations with ANP for 322 bird species to test whether small‐scale predictions related to breeding habitat, migratory behaviour, body mass and vocal traits are consistent at broad spatial extents for an extensive group of species.

    Location

    Conterminous USA.

    Time period

    2004–2011.

    Major taxa studied

    North American breeding birds.

    Methods

    We calculated, for each species, the association between the breeding season and ANP, using spatially explicit estimates of ANP from the National Park Service and weekly estimates of probabilities of occurrence based on observations from the eBird citizen‐science database. We evaluated how the association of the breeding season for each species with ANP was related to expectations based on size, migratory behaviour and breeding habitat. For a subset of species, we used vocal trait data for song duration, pitch and complexity to evaluate hypotheses from the birdsong literature related to habitat complexity and sensitivity to ANP.

    Results

    Species that breed predominantly in anthropogenic environments were associated with twice the level of ANP (~7.4 dB) as species breeding in forested habitats (~3.2 dB). However, we did not find evidence to suggest that birds with higher‐pitched songs are more likely to be found in areas with higher levels of ANP. Residents and migratory species did not differ in associations with ANP, but songs were less complex among forest‐breeding species than non‐forest‐breeding species and increased in complexity with increasing ANP.

    Main conclusions

    Anthropogenic noise pollution is an important factor associated with breeding distributions of bird species in North America. Vocal traits could be useful to understand factors that affect sensitivity to ANP and to predict the potential impact of ANP, although future studies should aim to understand how and why patterns differ across spatial scales.

     
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