to nesting in colonies could be the ability to share and procure information about food sources from neighbouring birds while raising chicks. While research has not been conducted on cave swallows themselves, some studies have been done on the closely related cliff and bank swallows. Cliff swallow nesting colonies have been suggested to serve as "information centres", where swallows can gather and glean information from one another regarding how well they are foraging. Cliff swallows have been observed to follow, or be followed by, other birds within the nesting colony to food sources; birds that were unsuccessful foraging will return to the colony to find a fellow roost-mate that has been successful, and which they will then follow to a food source. Bank swallows, however, do not appear to use small nesting colonies (26-52 nesting pairs is considered a small colony) as "information centres", but the cliff swallow colonies previously mentioned were large colonies in which there are more potentially successful foragers for other birds to follow. Reproduction As previously mentioned, North American subspecies of cave swallows roost and nest primarily in caves and sinkholes while the South American subspecies prefer open spaces such as cliff-faces and the sides of buildings. Breeding occurs between April and August. North American subspecies are currently undergoing a human-facilitated range expansion due to the increased availability of alternative nesting sites. These include highway culverts and bridges. In Texas alone cave swallows have increased their breeding range 898% between 1957 and 1999, with populations increasing at a rate of about 10.8% each year. Cave swallows are open-cup nesters, meaning they build a nest shaped like a cup with the top left open for them to fly in and out. The nests are made of mud and bat guano and can be reused for multiple breeding seasons. Old barn swallow nests are also utilized by cave swallows, which will modify them to suit their needs. Barn swallows and cave swallows are observed to co-exist at some nesting sites, making old barn swallow nests easily available to the cave swallow. Cave swallows are social and prefer to nest in variably sized colonies. They are even observed to occasionally share nest sites with other species of swallows, such as barn swallows. This occurs particularly often in north central Mexico and increasingly in the United States with the increased use of highway culverts as nesting sites. Some concerns have