Do supplemental perches influence electrocution risk for diurnal raptors?

Background:Power lines are amongst the main causes of mortality for birds globally.Electrocution drives the population dynamics of several threatened species of raptors,at local and global scales.Among the many solutions that have been tested to minimize this threat are supplemental perches;however,their efficiency has rarely been assessed.Methods:We designed 43 transects in 4 districts in mainland Portugal to gather data from birds perching on pylons with or without supplemental perches.From 2015 to 2018,transects were surveyed by car at least once.We analyzed the factors driving the use of these supplemental perches,and we analyzed if there were differences in the perceived risk(calculated from measurements and not from field surveys)depending on whether the perching was on pylons with or without supplemental perches.Results:We recorded 548 perches of 14 species.Weather conditions seemed to play a role in birds’choice of pylons with supplemental perches versus pylons without supplemental perches.Models also indicated a strong influence of observational conditions.The use of models showed us an important specific effect in the selection of supplemental perches where available:there are some species with a greater tendency to perch on supplemental perches,even when they use both pylons with and without supplemental perches.For most of the analyzed species and species groups,perceived risk was higher in pylons without supplemental perches compared to pylons with supplemental perches,but there were differences between species.Conclusions:Supplemental perches may be a useful and efficient tool for mitigating raptor electrocution.However,there are many influential factors affecting their success,and their effectiveness with different species groups is not homogeneous.Some studies show higher electrocution rates for certain species and devices and thus,their efficacy must be validated.We propose a two-step validation process,first in controlled conditions and then in the field.A common protocol should be established to enable comparisons between studies.

Wind effects on the migration routes of trans-Saharan soaring raptors： geographical, seasonal, and interspecific variation

Wind is among the most important environmental factors shaping birds＇ migration patterns. Birds must deal with the displacement caused by crosswinds and their behavior can vary according to different factors such as flight mode, migratory season, experience, and distance to goal areas. Here we analyze the relationship between wind and migratory movements of three raptor species which migrate by soaring-gliding flight： Egyptian vulture Neophron percnopterus, booted eagle Aquila pennata, and short-toed snake eagle Circaetus gallicus. We analyzed daily migratory segments （i.e., the path joining consecutive roosting locations） using data recorded by GPS satellite telemetry. Daily movements of Egyptian vultures and booted eagles were significantly affected by tailwinds during both autumn and spring migrations. In contrast, daily movements of short-toed eagles were only significantly affected by tailwinds during autumn migration. The effect of crosswinds was signifi- cant in all cases. Interestingly, Egyptian vultures and booted eagles showed latitudinal differences in their behavior： both species compensated more frequently at the onset of autumn migration and, at the end of the season when reaching their wintering areas, the proportion of drift segments was higher. In contrast, there was a higher drift at the onset of spring migration and a higher compensation at the end. Our results highlight the effect of wind patterns on the migratory routes of soaring raptors, with different outcomes in relation to species, season, and latitude, ultimately shaping the loop migration patterns that current tracking techniques are showing to be widespread in many long distance migrants.