Desert crossing strategies of migrant songbirds vary between and within species.

Each year, billions of songbirds cross large ecological barriers during their migration. Understanding how they perform this incredible task is crucial to predict how global change may threaten the safety of such journeys. Earlier studies based on radar suggested that most songbirds cross deserts in intermittent flights at high altitude, stopping in the desert during the day, while recent tracking with light loggers suggested diurnal prolongation of nocturnal flights and common non-stop flights for some species. We analyzed light intensity and temperature data obtained from geolocation loggers deployed on 130 individuals of ten migratory songbird species, and show that a large variety of strategies for crossing deserts exists between, but also sometimes within species. Diurnal stopover in the desert is a common strategy in autumn, while most species prolonged some nocturnal flights into the day. Non-stop flights over the desert occurred more frequently in spring than in autumn, and more frequently in foliage gleaners. Temperature recordings suggest that songbirds crossed deserts with flight bouts performed at various altitudes according to species and season, along a gradient ranging from low above ground in autumn to probably >2000 m above ground level, and possibly at higher altitude in spring. High-altitude flights are therefore not the general rule for crossing deserts in migrant songbirds. We conclude that a diversity of migration strategies exists for desert crossing among songbirds, with variations between but also within species.

Unravelling migration connectivity reveals unsustainable hunting of the declining ortolan bunting.

In France, illegal hunting of the endangered ortolan bunting Emberiza hortulana has been defended for the sake of tradition and gastronomy. Hunters argued that ortolan buntings trapped in southwest France originate from large and stable populations across the whole of Europe. Yet, the European Commission referred France to the Court of Justice of the European Union (EU) in December 2016 for infringements to legislation (IP/16/4213). To better assess the impact of hunting in France, we combined Pan-European data from archival light loggers, stable isotopes, and genetics to determine the migration strategy of the species across continents. Ortolan buntings migrating through France come from northern and western populations, which are small, fragmented and declining. Population viability modeling further revealed that harvesting in southwest France is far from sustainable and increases extinction risk. These results provide the sufficient scientific evidence for justifying the ban on ortolan harvesting in France.

Eggshell thinning of osprey (Pandion haliaetus) breeding in Sweden and its significance for egg breakage and breeding outcome.

In the middle of the 1960s low reproductive rate was found in several osprey (Pandion haliaetus) nests in Sweden. Therefore a project was started to investigate the production and to collect unhatched eggs and shell fragments in different regions of Sweden during 1971-2008. Measurements of osprey eggs from museum collections from 1840 to 1970 were included to study long-term changes in shell thickness. In total, eggshell thickness of whole eggs from 666 clutches and of shell fragments from 693 nests was measured. The thinnest shell fragments were recorded in 1973 (mean for 71 clutches: 0.438 mm), minus 15.0% compared to thickness of unaffected eggs before 1946 (0.515 mm). After 1973, shell thickness increased to reach background levels in 2003 (0.515 mm). Thus, it took 30 years to reach full thickness again. From the start of the decrease it took more than 50 years to reach unaffected conditions. The number of whole eggs remaining intact in the nest throughout incubation was reduced when shell thickness decreased. Great loss of eggs due to breakage seems to occur when the mean shell thickness in the clutch was below 0.40 mm. In 1971-1973, when shell thinning was most pronounced, the average thickness of shell fragments was 0.366 mm in nests with 0 intact eggs (minus 29% compared to the pre-1946 background value); 0.393 mm (minus 24%) in nests with 1 intact egg; 0.431 mm (minus 16%) in nests with 2 intact eggs and 0.450 mm (minus 12%) in nests with 3 intact eggs. Differences in thickness were significant for 1 versus 2 intact eggs, 2 vs. 3 intact eggs and for 0+1 vs. 2+3 intact eggs. Actual data from the period 1971-73 shows a decline in the production of young (4-5 weeks) of some 15% (0.25 young per nest).