Abstract
AbstractAimTo show how recent declines in populations of long‐distance migrant birds are associated with recent increases in human population growth and agricultural intensification on their tropical non‐breeding grounds, except for synanthropic species, where we expect the reverse.LocationBreeding populations throughout Europe and North America spending the non‐breeding season throughout Africa, and Central and South America, respectively.MethodsWe mapped 50 species of long‐distance migrant birds from published tagging studies of 126 breeding populations and identified their breeding population trends from 2000 to 2015 from published Country or State census data. We then matched individual bird non‐breeding locations, from each population, to local human population change and crop yield data. We used GLMs to predict whether bird population decline was associated with human population change or crop yield and whether this was dependent on if a species was synanthropic or not, controlling for absolute human population density, breeding and non‐breeding location, migratory distance and phylogeny. We predicted that bird populations that spend the non‐breeding season in areas of recent higher human population increase or agricultural intensification (crop yield) would show greater declines, but that declines would be less for species that frequently utilize anthropogenic habitats such as secondary woodland and farmland.ResultsBird population change, even for synanthropic species, showed a significant negative relationship with relative human population change and crop yield (but this was weak, <2% and 6% of variance respectively), and this relationship was the same for the Neotropics and Africa, despite African human population change being three times larger.Main conclusionsThe results suggest that local human population change in the non‐breeding area is likely to be only a relatively minor driver of migrant declines, and its effects may be through increases in agricultural intensification reducing carrying capacity, but we currently lack local studies to confirm this.
Highlights
Migrant bird populations are declining globally, with major declines in both the Afro‐Palaearctic (Sanderson, Donald, Pain, Burfield, & Bommel, 2006; Vickery et al, 2014) and Neotropical (Holmes, 2007; Robbins, Sauer, Greenberg, & Droege, 1989) regions
Because human population growth is usually associated with land use change/intensification, which reduces carrying capacity for most species, we might expect a negative relationship between human and migrant bird population change in the non‐breeding area
The first is that the amount of variance in bird population declines accounted for by human population change on the non‐breeding ground is relatively small, and the second is that whether or not a species favours anthropogenic habitats apparently makes little difference
Summary
Migrant bird populations are declining globally, with major declines in both the Afro‐Palaearctic (Sanderson, Donald, Pain, Burfield, & Bommel, 2006; Vickery et al, 2014) and Neotropical (Holmes, 2007; Robbins, Sauer, Greenberg, & Droege, 1989) regions. Because human population growth is usually associated with land use change/intensification, which reduces carrying capacity for most species, we might expect a negative relationship between human and migrant bird population change in the non‐breeding area. It is important, to consider change in human population density rather than absolute human population density because we are interested in a dynamic process of how bird populations change and because bird population trend data cover a wide range of starting populations that likely will have already been affected by human population density. We would expect synanthropic species to show weaker declines or even increases where rate of human population increase is greater because synanthropic species would benefit from increased availability of suitable habitat, but still to show a negative correlation between bird population trend and crop yield
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
