No abstract

Populations of migratory songbirds in western Europe show considerable variation in population trends between species and regions. The demographic and environmental causes of these large-scale patterns are poorly understood. Using data from Constant Effort mist-netting studies, we investigated relationships between changes in abundance, adult survival and seasonal weather conditions among 35 western European populations of eight species of migratory warblers (Sylviidae). We used cross-species and withinspecies comparisons to assess whether annual variation in survival was correlated with weather conditions during passage or winter. We estimated survival using CJS markrecapture models accounting for variation in the proportion of transient individuals and recapture rates. Species wintering in the humid bioclimatic zone of western Africa had significantly higher annual survival probabilities than species wintering in the arid bioclimatic zone of Africa (the Sahel). Rainfall in the Sahel was positively correlated with survival in at least some populations of five species. We found substantially fewer significant relationships with indices of weather during the autumn and spring passage periods, which may be due to the use of broad-scale indices. Annual population changes were correlated with adult survival in all of our study species, although species undergoing widespread declines showed the weakest relationships.

Biodiversity is threatened by the growth of urban areas. However, it is still poorly understood how animals can cope with and adapt to these rapid and dramatic transformations of natural environments. The COVID-19 pandemic provides us with a unique opportunity to unveil the mechanisms involved in this process. Lockdown measures imposed in most countries are causing an unprecedented reduction of human activities, giving us an experimental setting to assess the effects of our lifestyle on biodiversity. We studied the birds' response to the population lockdown by using more than 126 000 bird records collected by a citizen science project in northeastern Spain. We compared the occurrence and detectability of birds during the spring 2020 lockdown with baseline data from previous years in the same urban areas and dates. We found that birds did not increase their probability of occurrence in urban areas during the lockdown, refuting the hypothesis that nature has recovered its space in human-emptied urban areas. However, we found an increase in bird detectability, especially during early morning, suggesting a rapid change in the birds’ daily routines in response to quieter and less crowded cities. Therefore, urban birds show high behavioural plasticity to rapidly adjust to novel environmental conditions, such as those imposed by the COVID-19.

Aim As global temperatures have increased, many species distributions have exhibited polewards shifts, a trend that is predicted to continue in future decades. However, the mechanisms underlying such shifts are not well understood. Here we quantify the impact of large-scale variation in temperature on reproductive output within a group of migratory birds to assess the potential for future range changes. Location Western Europe.Methods We use data from captures of 350,000 individual birds, collected under constant effort ringing protocols from 1994-2006, to estimate productivity (percentage of juveniles caught) for seven species of migrant warblers (family Sylviidae) breeding in Europe in relation to spring temperature and latitude by fitting generalized linear mixed models. ResultsProductivity was highest at mid-latitudes for six of our seven study species and did not change significantly over the study period. Only one species (reed warbler, Acrocephalus scirpaceus) showed increased productivity at northern sites as expected. Six of the seven species also showed evidence for local adaptation, with productivity decreasing as temperatures diverged from the local mean. However, for three of these species the 'optimum' temperature was greater than the local mean temperature at the majority of sites. Main conclusionsThese results indicate that latitudinal gradients in productivity are likely to influence large-scale abundance patterns, but that adaptation to local climate conditions has the potential to constrain the rate of northward range shifts in many species.

Gargallo (2013) Site-and species-specific fuel load of European-Afrotropical passerines on arrival at three oases of southeast Morocco during spring migration, Bird Study, 60:1, 11-21,