Weak Effects of Geolocators on Small Birds: A Meta-analysis Controlled for Phylogeny and Publication Bias

Currently, the deployment of tracking devices is one of the most frequently used approaches to study movement ecology of birds. Recent miniaturization of light-level geolocators enabled studying small bird species whose migratory patterns were widely unknown. However, geolocators may reduce vital rates in tagged birds and may bias obtained movement data. There is a need for a thorough assessment of the potential tag effects on small birds, as previous meta-analyses did not evaluate unpublished data and impact of multiple life-history traits, focused mainly on large species and the number of published studies tagging small birds has increased substantially. We quantitatively reviewed 549 records extracted from 74 published and 48 unpublished studies on over 7,800 tagged and 17,800 control individuals to examine the effects of geolocator tagging on small bird species (body mass <100 g). We calculated the effect of tagging on apparent survival, condition, phenology and breeding performance and identified the most important predictors of the magnitude of effect sizes. Even though the effects were not statistically significant in phylogenetically controlled models, we found a weak negative impact of geolocators on apparent survival. The negative effect on apparent survival was stronger with increasing relative load of the device and with geolocators attached using elastic harnesses. Moreover, tagging effects were stronger in smaller species. In conclusion, we found a weak effect on apparent survival of tagged birds and managed to pinpoint key aspects and drivers of tagging effects. We provide recommendations for establishing matched control group for proper effect size assessment in future studies and outline various aspects of tagging that need further investigation. Finally, our results encourage further use of geolocators on small bird species but the ethical aspects and scientific benefits should always be considered.Grantova Agentura Ceske Republiky 13-06451SInstitut Polaire Francais Paul Emile Victor IPEV-1036Institutional Research Plan RVO: 68081766Leverhulme Trust RPG-2013288Russian Foundation for Basic Research Arctic-18-05-60261Russian Science Foundation 17-14-0114

Spatiotemporal patterns of egg laying in the common cuckoo

Understanding egg-laying behaviour of brood parasites in space and time can improve our knowledge of interactions between hosts and parasites. However, no studies have combined information on the laying activity of an obligate brood parasite with detailed information on the distribution of host nests within an area and time period. Here, we used molecular methods and analysis of egg phenotypes to determine maternal identity of common cuckoo, Cuculus canorus, eggs and chicks found in the nests of four species of Acrocephalus warblers in consecutive years. The median size of a cuckoo female laying area (calculated as a minimum convex polygon) was correlated negatively with the density of host nests and positively with the number of eggs assigned to a particular female. Cuckoo female laying areas overlapped to a large extent and their size and location did not change between years. Cuckoo females preferentially parasitized host nests located close to their previously parasitized nests and were mostly host specific except for two that parasitized two host species. Future studies should focus on sympatric host and parasite communities with variable densities across different brood-parasitic systems to investigate how population density of hosts affects fitness and evolution of brood parasites. For instance, it remains unknown whether female parasites moving to new sites need to meet a threshold density of a potential host. In addition, young females may be more limited in their egg laying, particularly with respect to the activity of other parasites and hosts, than older females

Population trends of ground-nesting birds indicate increasing environmental impacts from Eastern to Western Europe: different patterns for open-habitat and woodland species

Introduction: Bird populations reflect the influence of major environmental changes, and the analysis of their long-term population trends concerning species-specific ecological traits can provide insight into biologically relevant impacts of such changes. In this respect, nest site is a particularly informative trait because ground-nesting bird species are more prone, in contrast to species nesting above the ground, to the impacts of nest predation which can be linked to various environmental drivers including the intensification of agriculture or woodland management. Here we hypothesize that a) ground-nesting species present negative trends due to environmental pressures mentioned above, b) such declining trends should be more pronounced in Western than in Eastern Europe because, in Western countries, the environmental threats are likely greater, and c) the interaction between nest site and habitat association will point at the habitat types where the presumed drivers most likely operate.Methods: We used population trends from 1980 to 2016 of 332 bird species in 16 European countries to test this hypothesis.Results: We found that the long-term population trends of ground-nesting birds are more negative than the trends of species nesting above the ground indicating the effect of nest predation, and this difference increased from Eastern to Western European countries, probably due to steeply increasing populations of nest predators in the West. However, the effect of longitude interacted with the habitat association being strong in woodland species and weak in open-habitat species.Discussion: This pattern suggests that the increased nest predation pressure in the West is linked to woodlands, probably due to higher abundances of mammalian herbivores that destroy forest ground and shrub layer, and thus leave the nests exposed to predators. In contrast, only a weak longitudinal pattern in open-habitat species indicates that the negative impacts of agricultural intensification are no longer confined to the Western part of the continent. Although nature conservation activities are generally successful in Europe, as indicated by benefits provided by the Natura 2000 network, our results uncovered substantial gaps in delivering such benefits

Details on tracked birds and geolocators from Intra-tropical movements as a beneficial strategy for Palearctic migratory birds

Table S1. Capture year and number of captured and recaptured (with data for this paper / all recaptured) individuals, and technical details of geolocators (type, harness material, angle of light guide and mass [g]) used to track great reed warblers

Data used for the analysis of change in weekly NDVI around arrival and departure from Intra-tropical movements as a beneficial strategy for Palearctic migratory birds

ESM S3. Data used for the analysis of change in weekly NDVI during the two weeks around arrival at and around departure from individual sites. See ESM S1 for data description and R code

Data used for the analysis of difference in mean NDVI between nonbreeding sites from Intra-tropical movements as a beneficial strategy for Palearctic migratory birds

ESM S2. Data used for the analysis of difference in mean NDVI between nonbreeding sites when the birds were present and when they stayed at the other nonbreeding site. See ESM S1 for data description and R code

Nonbreeding sites of the tracked great reed warblers with the quartiles in longitude and latitude from Intra-tropical movements as a beneficial strategy for Palearctic migratory birds

Figure S1. Nonbreeding sites of 29 great reed warblers from central European population and 17 birds from south-eastern European population. Individual positions are expressed as the centres of the highest density distributions of daily positions (modes; filled circles) and the 1st and 3rd quartiles in longitude and latitude (lengths of crossing vertical and horizontal bars)

Magnitude and direction of population trends, ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012

Magnitude and direction of population trends (1 = 100%), ecological and life-history traits of 36 passerine species breeding in Europe between 2001 and 2012. Non-breeding niche position varies from 1 (closed forest) to 7 (open country) and non-breeding niche breadth expresses the difference between the values of the two main habitats; non-breeding habitat wetness scores from (1) dry to (3) aquatic habitats. Non-breeding regions: (1) west–central region, (2) west–east region, (3) central–south region, (4) ‘entire’ region. Breeding habitat: forest (F), wetland (W), urban (U) and open habitat (O). PC 1 expresses a gradient from ‘slower strategy’ (K-selected) species to ‘faster strategy’ (r-selected) species. PC 2 depicts a gradient from species allocating most of their energy to just one breeding attempt per season to species spreading their investments across multiple breeding attempts per season

Multiple parasitism in an evictor brood parasite: Patterns revealed by long-term monitoring, continuous video-recording and genetic analyses

In some populations of host of brood parasites, more than two parasite eggs may be laid in a single nest. This phenomenon is known as multiple parasitism, representing a cost to both host and parasite. In this study, we analysed a long-term dataset (2007–2021) focusing on multiple parasitism of the common cuckoo (Cuculus canorus) parasitizing the great reed warbler (Acrocephalus arundinaceus). Annual parasitism rate was on average 54.3% and varied between 5.8% and 92.2%, depending on the year. From 720 parasitized nests, double parasitism was recorded in 172 (23.9%) nests, triple in 51 (7.1%) nests, quadruple in 10 (1.3%) nests and, exceptionally, in the years of heavy parasitism (about 90%), quintuple parasitism was recorded in three (0.4%) nests. The rate of multiple parasitism ranged from 0% to 63% inter-annually and strongly correlated with parasitism rate and total number of parasite eggs found. Furthermore, the number of cuckoo eggs laid per one nest increased with decreasing daily availability of host nests that were at a suitable breeding stage for parasitism. Both genetic and egg phenotype analyses revealed that no cuckoo female laid more than one egg in the same host nest. Using data on long-term parasite–host interactions and from continuous video-recording, as well as progressive methods to assign parasite offspring thus helped us better understand various aspects of multiple parasitism in hosts heavily parasitized by an evictor brood parasite