Changes in bird‐migration patterns associated with human‐induced mortality

Abstract

Many bird populations have recently changed their migratory behavior in response to alterations of the environment. We collected data over 16 years on male Great Bustards (Otis tarda), a species showing a partial migratory pattern (sedentary and migratory birds coexisting in the same breeding groups). We conducted population counts and radio tracked 180 individuals to examine differences in survival rates between migratory and sedentary individuals and evaluate possible effects of these differences on the migratory pattern of the population. Overall, 65% of individuals migrated and 35% did not. The average distance between breeding and postbreeding areas of migrant individuals was 89.9 km, and the longest average movement of sedentary males was 3.8 km. Breeding group and migration distance had no effect on survival. However, mortality of migrants was 2.4 to 3.5 times higher than mortality of sedentary birds. For marked males, collision with power lines was the main cause of death from unnatural causes (37.6% of all deaths), and migratory birds died in collisions with power lines more frequently than sedentary birds (21.3% vs 6.3%). The percentage of sedentary individuals increased from 17% in 1997 to 45% in 2012. These results were consistent with data collected from radio-tracked individuals: The proportion of migratory individuals decreased from 86% in 1997-1999 to 44% in 2006-2010. The observed decrease in the migratory tendency was not related to climatic changes (temperatures did not change over the study period) or improvements in habitat quality (dry cereal farmland area decreased in the main study area). Our findings suggest that human-induced mortality during migration may be an important factor shaping the migration patterns of species inhabiting humanized landscapes.

Fitness consequences of different migratory strategies in partially migratory populations: A multi‐taxa meta‐analysis

“…Increasing infrastructure and land‐use change may also add to mortality risks associated with migration. The construction of power lines, for instance, is associated with greater mortality in migrating birds (Palacín et al, ), while agricultural intensification, damming and hunting are all thought to have negative consequences for migratory birds (Adams, Small, & Vickery, ; Vickery et al, ).…”

“…These generally predict that migration confers survival benefit as it allows individuals to escape unfavourable climatic conditions and low resource abundance, while residency promotes breeding success through early access to better resources—such as territories or breeding locations (Chapman et al, ; Kokko, ; Lundberg, ). Although relative fitness benefits have been quantified in many partially migratory populations (Bai, Severinghaus, & Philippart, ; Hansen, Aanes, & Sæther, ; Hebblewhite & Merrill, ; Palacín, Alonso, Martín, & Alonso, ), the generality of this prediction across taxa has not been tested previously. Assessing the prevalence of fitness parity between migrants and residents—and any patterns evident in the deviation from this parity—has the potential to add to our understanding of the ontogeny of migratory behaviours, as well as shed light on how migratory species will respond to increasing anthropogenic threats.…”

“Closer‐to‐home” strategy benefits juvenile survival in a long‐distance migratory bird

“…In recent years, numerous studies have shown that birds alter their migratory behavior by changing their routes and/ or timing, dynamically altering their wintering strategies, or even becoming residents (Fiedler, 2003;Palacín et al, 2017;Visser, Perdeck, Balen, & Both, 2009). In recent years, numerous studies have shown that birds alter their migratory behavior by changing their routes and/ or timing, dynamically altering their wintering strategies, or even becoming residents (Fiedler, 2003;Palacín et al, 2017;Visser, Perdeck, Balen, & Both, 2009).…”

Meta‐barcoding insights into the spatial and temporal dietary patterns of the threatened Asian Great Bustard (Otis tarda dybowskii) with potential implications for diverging migratory strategies

“…We hypothesize this is a contributing factor to the recent shift to nonmigratory strategies in TMJ, as there is a significant difference in species abundance and consumption of plant species between the nonmigratory TMJ birds, and those migrating to WN and CZ. However, we note that climate change and other factors cannot be ruled out (Alonso, Salgado, & Palacín, ; Palacín, Alonso, Martín, & Alonso, ; Palacín & Martín, ).…”