The common swift, the barn swallow, and the house martin are three urban, insect-eating birds whose populations are declining in many parts of Europe. Yet they continue to play a vital role in pest control, making their protection an important priority. They are not the only birds that act as natural pesticides, but they are among the most influential in cities today.
Despite their status as allies to people, the main threats to these migratory species are the destruction of nesting sites and the widespread use of pesticides.
The Spanish Society of OrnithologySEO-BirdLife and Ecologistas en Acción have campaigned for years to protect the three most abundant insectivorous birds in Spanish cities. These are the neighborhood birds that return to Spain’s towns each spring, providing clear benefits in pest control for crops and public health alike.
All three species receive strict legal protection, so removing breeding grounds and destroying nests are crimes that should be prosecuted. However, nesting often occurs on buildings, making nests highly visible. This visibility leads some people to frame it as an aesthetic or cleanliness issue.
Nest destruction mainly results from building renovations that close holes or remove eaves. In addition to new construction, smooth, featureless walls hinder the birds from colonizing other urban areas.
Other threats include pesticide use and urban air pollution, which reduce food availability and reproductive capacity. Climate change is also affecting migration patterns and timing.
Data collected by Ecologistas en Acción on the spring population trends of these birds from 1998 to 2019 show a marked decline: roughly 27.2% for swallows and even larger declines for other species. It is estimated that about one million individuals are lost each year in Spain for one of these species.
They constantly eat insects
The diet of these birds is predominantly insects. Swifts feed on flies and mosquitoes, while swallows target bedbugs and various small insects. Scientific studies have found up to 445 prey items in the digestive tracts of swift species in Spanish territory, with insects making up more than 99% of these items.
A single swallow can consume around 850 flies and mosquitoes per day, totaling more than 310,000 per year. This clearly benefits agriculture and public health through natural pest control.
Thus, the feeding capacity of these birds represents a crucial ecosystem service for humans by reducing pest pressures. Science recognizes the swift and barn swallow as natural predators of insects that threaten crops, contributing to healthier ecosystems.
Protecting the survival of swifts, swallows, and martins requires strong support from municipal administrations and a clear, long-term commitment.
That is why campaigns like Three Flappers aim to secure regulatory measures in Spanish municipalities to support urban conservation of these bird populations.
Other planned actions include creating new colonies, preventing disturbances, and providing tools to monitor existing populations through censuses.
The swift and the swallow are among the most threatened today. SEO/BirdLife estimates that about one million barn swallows are lost in Spain each year, a figure that highlights a broader European trend that is even more acute.
Barn swallow populations have seen declines of about 41% from 1998 to 2012 and another 33% in the last decade. A study by a non-governmental organization suggests the probability of extinction of the species on the Iberian Peninsula within the next century could be about 10%. Despite these challenges, the swallow is listed as threatened in only a few autonomous communities, including Andalusia, the Balearic Islands, Castilla-La Mancha, and Extremadura.
Here are some key characteristics of these birds:
Common Swift (apus apus)
Common swifts are highly social birds that nest in colonies on building facades, even in large cities. Though migratory, a minimum wintering presence has been observed in the southwestern part of Spain in recent years. They can be seen in the country from February to October, and the population in Spain is the largest in Europe.
Swifts measure about 13 to 15 cm in length, with a wingspan of 26 to 28 cm and a body weight around 18 g. They are dark above with a pale underbelly, and their wings are long and pointed. The tail is short and forked, the beak is short and straight, and the mouth is very wide.
They are highly vocal, often producing chirps or quick, sharp calls. Natural predators include owls, magpies, and other larger birds, and in some countries such as Portugal, artificial nesting structures have shown success in supporting populations.
Barn Swallow (hirundo rustica)
The barn swallow is one of the most studied birds in science, contributing to our understanding of migration and reproduction. Its arrival is traditionally seen as a herald of spring, though climate change is altering timing. It nests in colonies and can be observed in Spain from February to October.
It measures about 14 to 19 cm in length, with a wingspan around 33 cm and a weight of 16 to 22 g. Its plumage is black with metallic blue on top and creamy white beneath, with a red forehead and throat and a black collar. The wings are long and pointed, the tail is very long and deeply forked with white markings when extended, and the beak is short and black.
The barn swallow is a prolific singer, with a repertoire that includes choral bursts and rapid, ringing chirps ending in a harsh grrr. It is also known for frequent calls such as a high-pitched uit, uit. Predators include hawks, owls, and domestic cats.
Common House Martin (delichon urbicum)
House martins epitomize the extreme adaptation of birds to aerial life. With the exception of nesting, much of their life can be spent in flight. They are a migratory species that winters in sub-Saharan areas but breeds in urban environments in many parts of Europe. In Spain, they can be seen from April to September.
They have a wingspan of 42 to 47 cm, a body length of 16 to 17 cm, and weigh about 40 g. They appear dark brown to nearly black above, with a white throat and a compact body. Their wings are narrow and long, and their legs are short and not suited for perching on the ground. The beak is short and straight, and the mouth is wide.
The swift has a distinctive song, delivering a short, monotonous high-pitched trill. Females emit a softer suii, while males sound srii; together they create the characteristic song of the species. The species has few local populations and tends to favor urban nesting sites.
While the population data remain a concern, ongoing efforts by conservation groups continue to push for urban planning that accommodates these birds, including the installation of nesting boxes and protections during renovation work.
— End of overview for the three insectivorous urban birds and their conservation status as of today, with emphasis on the importance of policy and community actions to safeguard their habitats and ecological services for humans. (SEO-BirdLife)