Tree Swallows (Tachycineta bicolor) are voracious consumers of flying insects within wetland and riverine systems. They typically produce large clutch sizes ranging from five to seven eggs which cause a high demand for food. Together, the adults and chicks can consume hundreds of thousands of insects during a single breeding season. This creates the potential for Tree Swallows to make a significant dent in the insect pest population.

The Santa Ana River hosts huge numbers of midges and mosquitoes which are a nuisance to recreationalists and residents along the river. The Orange County Water District and partnering agencies have taken a strong stance to invest heavily in environmentally-friendly approaches in dealing with nuisance insects in the Santa Ana River.

The Orange County Water District has adopted a biological control approach in using avian allies, such as swallows to assist in controlling these insects. Residents walking along the river can see the placement of hundreds of nest boxes mounted atop fences, in trees, and on metal poles. This program is an extension of a Water District program initiated behind the Prado Dam 10 years ago. That program routinely achieves 100% occupancy of the nest boxes and has documented nearly 5,000 Tree Swallow fledglings.

Other species of swallows also nest along the river including Cliff Swallows, Barn Swallows, and Northern Rough-winged Swallows. Taken together with Tree Swallows, these aerial predators are consuming millions of midges every year. While it is not reasonable to expect that these birds can completely control the problem, it has been estimated that they are at least as effective as the historic use of pesticides.