How hazardous is the Sahara Desert crossing for migratory birds? Indications from satellite tracking of raptors

Abstract

We investigated the risk associated with crossing the Sahara Desert for migrating birds by evaluating more than 90 journeys across this desert by four species of raptors (osprey Pandion haliaetus, honey buzzard Pernis apivorus, marsh harrier Circus aeruginosus and Eurasian hobby Falco subbuteo) recorded by satellite telemetry. Forty per cent of the crossings included events of aberrant behaviours, such as abrupt course changes, slow travel speeds, interruptions, aborted crossings followed by retreats from the desert and failed crossings due to death, indicating difficulties for the migrants. The mortality during the Sahara crossing was 31 per cent per crossing attempt for juveniles (first autumn migration), compared with only 2 per cent for adults (autumn and spring combined). Mortality associated with the Sahara passage made up a substantial fraction (up to about half for juveniles) of the total annual mortality, demonstrating that this passage has a profound influence on survival and fitness of migrants. Aberrant behaviours resulted in late arrival at the breeding grounds and an increased probability of breeding failure (carry-over effects). This study also demonstrates that satellite tracking can be a powerful method to reveal when and where birds are exposed to enhanced risk and mortality during their annual cycles.

Seasonal migration to high latitudes results in major reproductive benefits in an insect

“…Numerous insect species, comprising members of several insect orders, migrate poleward from lower-latitude winter habitats each spring to exploit temporary resources where they can reproduce during the summer but are unable to survive over winter (2)(3)(4)(5)(6)(7)(8)(9). Compared with our knowledge of the energetic costs, mortality risks, and reproductive benefits of bird migration (10)(11)(12)(13)(14)(15)(16), the adaptive benefits and population dynamics consequences of insect migration are poorly understood (6)(7)(8)(9). For most migratory insects, their low-latitude winter habitats are considered to be the major breeding grounds.…”

Climate change alters the optimal wind-dependent flight routes of an avian migrant

“…Investigating how climate change can disturb wind support for migratory species is crucial, particularly for species that depend on the wind to cross ecological barriers such as water bodies and deserts (e.g. [38,39]), and those that are predicted to be exposed to longer journeys due to range shifts caused by climate change [2].…”

Insights into the migration of the European Roller from ring recoveries

“…We tentatively argue that the lower relative recovery rate of juveniles in spring suggests a lower non-breeding survival in juveniles compared to adults, though these differences were not statistically significant. More formal studies of mortality during migration, though rare, generally show higher mortality in juveniles compared to adults (Johnson 1973;Owen and Black 1989;Strandberg et al 2009;Guillemain et al 2010;but see Grü ebler et al 2014).…”

“…is crucial for understanding patterns of connectivity and predicting the response of migratory populations to environmental change (Cresswell 2014). Additionally, knowing where and under what circumstances migrants die contributes to our understanding of how population size is regulated throughout the annual cycle (Strandberg et al 2009;Klaassen et al 2014).…”