Short-distance nocturnal migration in an island endemic bustard

Migratory birds typically fly long distances in response to large-scale seasonal climate variation. However, most migratory species are partial migrants, and some fly only short distances, for example to take advantage of suitable feeding conditions during the non-breeding season. In spite of their short distance, such migrations may also be fixed in populations as a result of evolutionarily adaptive responses to local habitat conditions, but the causes and details of these partial, short-distance migrations have been scarcely investigated. Here we analyse the migratory patterns of the insular endemic subspecies of Houbara Bustard Chlamydotis undulata fuertaventurae in a small island of the Canary archipelago. We tagged 41 individuals with GSM/GPRS loggers and tracked them over two annual cycles (2017-2019). We found that Canarian Houbara Bustards are short-distance, partial migrants. Once the mating season was over, more than one-third of all males and females moved from their breeding territories to non-breeding areas where they spent the hottest months of the year. No bird changed its migratory status between years, and most individuals showed interannual fidelity to their breeding and non-breeding areas. There were differences in the productivity of green vegetation between breeding and non-breeding areas, as estimated from remote-sensing-based indicators of vegetation productivity (Normalized Difference Vegetation Index and Soil-Adjusted Vegetation Index). During the non-breeding period, values of both indices were higher at the non-breeding than at the breeding areas in migratory birds, providing a plausible explanation of why these individuals moved to non-breeding areas rather than remaining in their territories. Moreover, during the non-breeding period, Soil-Adjusted Vegetation Index values were lower at breeding areas abandoned by migratory birds than at breeding areas occupied year-round, although values at the latter did not differ from those at non-breeding areas, suggesting that partial migration arises from variability in food availability during summer across different areas. One of the four non-breeding areas was selected by over half of migrant individuals. This area had a mosaic of cultivated and non-cultivated patches, with more fallow fields and irrigated farmland than the other areas. Finally, most migratory flights were performed at night. The Houbara Bustard is globally threatened, and given its vulnerability to collision with electric and telephone lines during migration, we recommend burying electric and telephone lines in high-traffic areas underground. Finally, we urge protection of the known non-breeding areas, and recommend that current farming condition practices and natural shrubland at these areas continue to provide suitable habitat for Houbara Bustards.

Automated summary

The Canarian Houbara Bustard is a short-distance, partial migratory bird species. After the breeding season, more than one-third of the individuals migrate from their breeding territories to non-breeding areas with higher vegetation productivity. Most individuals exhibit fidelity to their breeding and non-breeding areas across years.