This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km² combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.

The European population is estimated at 29-48.7 million pairs, which equates to 58-97.4 million mature individuals (BirdLife International 2015). Europe forms approximately 20% of the global range, so a very preliminary estimate of the global population size is 290-487 million mature individuals, although further validation of this estimate is needed. National population estimates include: 10,000-1 million breeding pairs and >1,000 individuals on migration in China; 10,000-100,000 breeding pairs, >10,000 individuals on migration and <50 wintering individuals in Taiwan; 10,000-1 million breeding pairs and >1,000 individuals on migration in Korea; 10,000-1 million breeding pairs, >1,000 individuals on migration and 50-1,000 wintering individuals in Japan, as well as 10,000-100,000 breeding pairs and 1,000-10,000 individuals on migration in Russia (Brazil 2009).

This species breeds in a wide range of climates and over a wide altitudinal range. It prefers open country, such as farmland where buildings provide nesting sites and where water is nearby. It is primarily a rural species in Europe and North America, whilst in north Africa and Asia it often breeds in towns and cities (Turner and Christie 2012). In Europe, it is superseded by the House Martin (Delichon urbicum) in urban areas (Turner and Rose 1989). 

The breeding season lasts from May to August. The nest is built by both sexes and is a cup or half-cup, made from mud pellets mixed with fibres such as dry grass, straw and horsehair and lined with dry grass and white feathers. Originally, nests were built in caves or on cliffs, but now almost always on artificial structures. Clutches consist of two to seven eggs (Turner and Christie 2012). 

Barn Swallow feeds almost entirely on flying insects (Snow and Perrins 1998). The species is migratory, with European birds wintering in sub-Saharan Africa (Hagemeijer and Blair 1997), although some individuals winter in southern and western Europe (Snow and Perrins 1998). Birds breeding in North America winter in South America, whilst birds breeding in East Asia winter in South Asia (Turner and Christie 2012).

The main threat to the species is the intensification of agriculture. Changes in farming practices, such as the abandonment of traditional milk and beef production, have resulted in a loss of suitable foraging areas. In addition, intensive livestock rearing, land drainage and the use of herbicides and pesticides all reduce the numbers of insect prey available. Suitable nest sites are often scarcer on modern farms. The species is susceptible to changes in climate, with bad weather in the wintering areas as well as the breeding grounds affecting breeding success (Tucker and Heath 1994). It is occasionally hunted for sport, and nests are sometimes removed as a nuisance. In North America, introduced House Sparrows (Passer domesticus) are serious nest-site competitors, taking over nests and destroying eggs and nestlings (Turner and Christie 2012).

Conservation Actions Underway

Bern Convention Appendix II. There are currently no known conservation measures for this species within Europe.

Conservation Actions Proposed

Large areas of suitable habitat need to be maintained for this species, through the continuation and promotion of low-intensity, traditional farming. In particular, this requires extensive livestock rearing, a reduction in pesticide use and the preservation of wetland areas and waterbodies (Tucker and Heath 1994). Nesting can be encouraged by providing wooden ledges or artificial nest cups made of cement and sawdust or papier maché (Turner and Christie 2012). Long term monitoring and further research into the impacts of climatic variation is also needed (Tucker and Heath 1994).