Summary 1.Researchers often attach transmitters and other devices to free-living birds without a clear understanding of potential deleterious consequences to their study organisms, and thus to their data. Studies investigating this topic have generally been limited to a single species or type of device. 2. To achieve a broader understanding we used a meta-analysis of 84 studies to ask: (1) Do devices have an overall effect on birds? (2) Which aspects of avian behaviour and ecology are affected? (3) What attributes of birds influence transmitter effects? (4) What attributes of devices influence their effects? (5) Are effects partially a consequence of capture and restraint? 3. We found a significant negative effect of devices on birds, both overall and for 8 of the 12 specific aspects analysed. The most substantial effects were that birds with devices had markedly increased energy expenditure and were much less likely to nest. 4. Effects were independent of attributes of the birds (sex, age, primary method of locomotion and body mass). We also found no evidence that proportionally heavier devices had greater effects, although researchers generally avoided using heavy devices. Breast-mounted and harness attachments increased device-induced behaviours such as preening, however, and the risk of deviceinduced mortality differed between attachment methods. 5. Other than foraging behaviours, no effects were a consequence of capture or restraint. 6. Synthesis and applications. We provide the first comprehensive evidence that transmitters and other devices negatively affect birds and may bias resulting data. Researchers should balance the benefits of using these techniques against potential costs to the birds and reliability of the data obtained.

Effects of small population size and reduced genetic variation on the viability of wild animal populations remain controversial. During a 35-year study of a remnant population of greater prairie chickens, population size decreased from 2000 individuals in 1962 to fewer than 50 by 1994. Concurrently, both fitness, as measured by fertility and hatching rates of eggs, and genetic diversity declined significantly. Conservation measures initiated in 1992 with translocations of birds from large, genetically diverse populations restored egg viability. Thus, sufficient genetic resources appear to be critical for maintaining populations of greater prairie chickens.

Recent field studies have suggested that the dynamics of West Nile virus (WNV) transmission are influenced strongly by a few key super spreader bird species that function both as primary blood hosts of the vector mosquitoes (in particular Culex pipiens) and as reservoir-competent virus hosts. It has been hypothesized that human cases result from a shift in mosquito feeding from these key bird species to humans after abundance of the key birds species decreases. To test this paradigm, we performed a mosquito blood meal analysis integrating host-feeding patterns of Cx. pipiens, the principal vector of WNV in the eastern United States north of the latitude 36 degrees N and other mosquito species with robust measures of host availability, to determine host selection in a WNV-endemic area of suburban Chicago, Illinois, during 2005-2007. Results showed that Cx. pipiens fed predominantly (83%) on birds with a high diversity of species used as hosts (25 species). American robins (Turdus migratorius) were marginally overused and several species were underused on the basis of relative abundance measures, including the common grackle (Quiscalus quiscula), house sparrow (Passer domesticus), and European starling (Sturnus vulgaris). Culex pipiens also fed substantially on mammals (19%; 7 species with humans representing 16%). West Nile virus transmission intensified in July of both years at times when American robins were heavily fed upon, and then decreased when robin abundance decreased, after which other birds species were selected as hosts. There was no shift in feeding from birds to mammals coincident with emergence of human cases. Rather, bird feeding predominated when the onset of the human cases occurred. Measures of host abundance and competence and Cx. pipiens feeding preference were combined to estimate the amplification fractions of the different bird species. Predictions were that approximately 66% of WNV-infectious Cx. pipiens became infected from feeding on just a few species of birds, including American robins (35%), blue jays (17%, Cyanocitta cristata), and house finches (15%, Carpodacus mexicanus).

Functional traits offer a rich quantitative framework for developing and testing theories in evolutionary biology, ecology and ecosystem science. However, the potential of functional traits to drive theoretical advances and refine models of global change can only be fully realised when species-level information is complete. Here we present the AVONET dataset containing comprehensive functional trait data for all birds, including six ecological variables, 11 continuous morphological traits, and information on range size and location. Raw morphological measurements are presented from 90,020 individuals of 11,009 extant bird species sampled from 181 countries. These data are also summarised as species averages in three taxonomic formats, allowing integration with a global phylogeny, geographical range maps, IUCN Red List data and the eBird citizen science database. The AVONET dataset provides the most detailed picture of continuous trait variation for any major radiation of organisms, offering a global template for testing hypotheses and exploring the evolutionary origins, structure and functioning of biodiversity.