Function of the uropygial gland in eiders (Somateria mollissima)

Background:The uropygial gland is an exocrine gland located above the tail of birds that produces a diverse range of biochemicals.It has been hypothesized to be involved in chemical protection,water-proofing and maintenance of plumage brightness.Although these not necessarily mutually exclusive functions have received some empirical support,there has been little empirical research on the function of water-proofing.Methods:Here we analyzed data for 229 individual eiders(Somateria mollissima)collected by Danish hunters during 2016-2018.Results:The Eider is a sea-duck that spends almost its entire life in sea water emphasizing water-proofing of the plumage.The size of the uropygial gland increased with body mass in males,but not in females,and it increased with age.The size of the uropygial gland decreased during winter. Eiders with small uropygial glands grew their feathers at a fast rate.Eiders with large wing areas had large uropygial glands. Conclusions:These findings are consistent with large uropygial glands playing a role in water-proofing during molt and foraging, but also that uropygial glands may play a role in chemical defense.

Abundance of insects and aerial insectivorous birds in relation to pesticide and fertilizer use

Background:The abundance of insects has decreased considerably during recent decades,resulting in current abundance showing 70-80%reductions in more than 15 studies across temperate climate zones.Dramatic reduc-tions in the abundance of insects are likely to have consequences for other taxa at higher trophic levels such as preda-tors and parasites.Pesticides,fertilizers and agricultural land use are likely candidates accounting for such reductions in the abundance of insects.Methods:Here we surveyed the abundance of flying insects,and the reduction in the abundance of insects as a consequence of intensive reduction in agricultural practice linked to fertilizer use and pesticide use.Finally we dem-onstrated consistency in abundance of birds among study sites.Results:We demonstrated that the use of fertilizers and pesticides had reduced the abundance of insects,with consequences for the abundance of insectivorous bird species such as Barn Swallows(Hirundo rustica),House Martins(Delichon urbicum)and Swifts(Apus apus).Juvenile Barn Swallows were negatively affected by the reduced abundance of insects and hence the reproductive success of insectivorous bird species.These effects imply that the abundance of insects could be reduced by the availability of insect food.Conclusions:These effects of intensive agriculture on insect food abundance are likely to have negative impacts on populations of insects and their avian predators.This hypothesis was validated by a reduction in the abundance of insects,linked to an increase in the abundance of fertilizers and a general change in farming practice.

Comparative urbanization of birds in China and Europe based on birds associated with trees

Urbanization effects on living organisms are spatially heterogeneous.Here we quantified the abundance of birds per tree in forested urban and rural habitats for 85,829 trees mainly in China and Europe.A population model was based on the assumption that:1)birds have a normally distributed habitat preference;2)an increase in population size linked to the habitat preference;3)a population size dependent on the habitat preference;and 4)the removal of a certain fraction of individuals giving rise to extinction.We tested for large-scale differences in the impact of urbanization on the frequency distribution of the difference in abundance between urban and rural habitats in China and parts of Europe.The difference in the frequency distribution of urban population density of birds in trees minus rural population density of birds in trees in China and Europe was statistically significant suggesting that the abundance of birds differed between trees in urban and rural habitats,but more so in China than in Europe.We hypothesize that more pronounced differences in China than in Europe may have arisen due to the Four Pests Campaign in 1958-1962 that resulted in death of hundreds of millions of birds(mainly tree sparrows Passer monfanus,but also numerous other less common species that were starting to become urbanized around 1960).Species that were less common in 1960 could not sustain reductions in population size in urban areas and hence these species are still rare or absent in urban areas today 60 years later.