Trillers arrive with spring and spread across the Iberian Peninsula
Three migratory species returning northward to Spain begin to show up as temperatures rise: the swallow, the common swift (delichon urbicum) and the common swift (apus apus). Through ongoing monitoring programs run by SEO/BirdLife, movements and migration routes are tracked in detail throughout the year, enabling a clearer view of their patterns across the peninsula.
Both Barn Swallow and House Martin occupy large swathes of Spain, with small, stable winter populations lingering in the southwest and in warmer pockets along the Mediterranean coast. Monitoring data reveal that migratory flocks enter Iberia from Africa via the Strait of Gibraltar, the Atlantic Andalusian coast, and the Mediterranean coast. River valleys often act as important corridors during journeys and, in some cases, as breeding grounds, according to SEO/BirdLife.
Areas at higher altitudes with colder, continental climates have historically been where these species appeared last; today they are increasingly found breeding in warmer regions as well.
Recent analyses from SEO/BirdLife’s Birds and Climate program indicate a slowdown in the Barn Swallow’s progress. The pace of arrivals in recent years does not match the faster breakthroughs seen in the late 20th century.
The importance of wind
Common Swift arrivals occur later, though winter observations persist. In spring and early summer, these birds flood many urban areas as they emerge in southern regions with a more Mediterranean climate. Swift populations are noted for rapid, long-distance movements, a pattern attributed in part to ecological pressures such as declines in insect populations.
SEO/BirdLife continues to monitor both progression and delays in Iberian arrivals, with wind as a crucial meteorological factor shaping these patterns. Winds crossing the Bosphorus are described as a key mechanism that opens and closes routes to the European continent for many species during breeding seasons, enabling movements into and out of Iberia.
Blas Molina, coordinator of SEO/BirdLife’s Birds and Climate program, notes that we are facing a new environmental reality where climate changes influence migration dynamics and behavior.
Beyond climate, human actions also play a significant role. It is important to acknowledge the broader shifts affecting these birds and their habitats as part of a general environmental change, rather than a single factor.
These three species migrate to sub-Saharan Africa after the breeding season and return to Spain in spring, still occupying large areas of the Sahel. The region south of the Sahara remains a critical wintering and staging area for many of these birds (citation: SEO/BirdLife).
Fire risk and habitat loss
The wintering grounds and migration routes of these three species are not free from risk. Drought in some African wintering regions, overexploitation of water resources, and the broader impacts of climate change threaten survival. Lakes such as Lake Chad are highlighted as notable indicators of environmental stress (citation: SEO/BirdLife).
In addition to habitat loss, fires and vegetation burning can remove roosting sites that these swallows and other insectivores rely on. Some places become gathering spots for thousands of birds at roosting sites, underscoring the vulnerability of communal habitats.
Insects are a limiting resource, and declining insect populations exacerbate the long migratory journeys these birds undertake. The combined pressures of habitat reduction, climate shifts, and food scarcity contribute to a broader decline in urban-dwelling birds and other aerial species that rely on city structures for shelter and nesting sites.
One of the most pressing threats is the loss of nesting and roosting enclaves due to building reclamation, repairs, or demolition. This shrinking space forces birds to adapt or abandon traditional sites. SEO/BirdLife has launched campaigns and proposals to promote biodiversity in new construction and renovations, encouraging integration of wildlife-friendly features in architectural designs to support nesting opportunities.
SEO/BirdLife’s Birds and Weather Tracker provides ongoing insights into these trends (citation: SEO/BirdLife). This resource helps track how climate and weather interact with avian movements and habitat use.
Notes: the content reflects contemporary observations and underscores the need to consider multiple factors—climate, human activity, and habitat management—in efforts to conserve migratory birds across the Iberian Peninsula.
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Environment department contact details have been omitted as part of this summary.