Swallows Then and Now
Barn Swallows nest in Europe, Asia, and Africa as well as America. Originally, they nested in caves, hollowed-out crevices beneath tree roots on cliffs and banks, and places like that. These nesting spots were rare and tricky to find, so there weren't very many Barn Swallows. But when people started building structures, swallows immediately started taking advantage of them. Swallows don't compete with humans for food, and humans quickly noticed that swallows eat mosquitoes and other flying insects, so people liked sharing their homes with them. Some cultures even believe that swallows nesting on a house bring good luck. As humans spread to more and more places and built larger and larger settlements, swallows increased right along with them. This is because no matter where swallows lived, there was abundant food for them--flying insects can be anywhere!
In some arid places swallows did not increase when people started building, but are now increasing, thanks to irrigation. How did this change things? By watering fields, farmers made mud available! After all, swallows need both a place to build their nest AND building materials!
When the first European ornithologists came to America, they were already familiar with Barn Swallows. On this continent they found swallows nesting on Native American buildings and structures. As more and more people settled here, building more and more places where swallows could nest, the swallow population increased.
Nowadays nesting structures are easy for swallows to find. They have more trouble finding flying insects now that people use pesticides. But as long as there are mosquitoes, houses, and barns, there will be Barn Swallows.
Try This! Research
We helped swallows by increasing their nesting sites. Swallows are not the only birds that have increased thanks to humans. Look at this chart to see some other species that have increased thanks to human activity. Research the nesting and food requirements for each species, and write them on the chart. Think about how people affect each of these nesting and food needs. Use a marker to highlight the nesting and/or food needs that humans make more abundant.