Management-Related Traffic as a Stressor Eliciting Parental Care in a Roadside-Nesting Bird: The European Bee-Eater Merops apiaster

摘要

Traffic is often acknowledged as a threat to biodiversity, but its effects have been mostlyudstudied on roads subjected to high traffic intensity. The impact of lower traffic intensity suchudas those affecting protected areas is generally neglected, but conservation-oriented activitiesudentailing motorized traffic could paradoxically transform suitable habitats into ecologicaludtraps. Here we questioned whether roadside-nesting bee-eaters Merops apiaster perceivedudlow traffic intensity as a stressor eliciting risk-avoidance behaviors (alarm calls and flockudflushes) and reducing parental care. Comparisons were established within DoñanaudNational Park (Spain), between birds exposed to either negligible traffic (ca. 0±10 vehiclesudper day) or low traffic intensity (ca. 10±90 vehicles per day) associated to management andudresearch activities. The frequencies of alarm calls and flock flushes were greater in areas ofudhigher traffic intensity, which resulted in direct mortality at moderate vehicle speeds ( 40udkm/h). Parental feeding rates paralleled changes in traffic intensity, but contrary to our predictions.udIndeed, feeding rates were highest in traffic-exposed nests, during working daysudand traffic rush-hours. Traffic-avoidance responses were systematic and likely involvedudcosts (energy expenditure and mortality), but vehicle transit positively influenced the reproductiveudperformance of bee-eaters through an increase of nestling feeding rates. Becauseudthe expected outcome of traffic on individual performance can be opposed when responsesudare monitored during mating (i.e. negative effect by increase of alarm calls and flockudflushes) or nestling-feeding period (i.e. at least short-term positive effect by increase of nestlingudfeeding rates), caution should be taken before inferring fitness consequences onlyudfrom isolated behaviors or specific life history stages.