Swallows are widely appreciated for their graceful flight and their association with human-made structures. Their annual return signals the warmer months, as they are renowned for constructing distinct nests in sheltered locations. Understanding their nesting habits provides insight into their life cycle and the ways they adapt to their environments.
The Nesting Season
Swallows begin their nesting activities in spring, with the breeding season extending through the summer months, from March to September. However, the precise timing can vary significantly based on geographical location. In some regions, swallows may start breeding as early as March, while in others, particularly more northern areas, nesting might commence in April or May.
Environmental conditions play a substantial role in influencing the start and duration of nesting. Factors such as temperature and rainfall directly impact the availability of flying insects, which are the primary food source for swallows. Prolonged cold or wet periods can delay nesting or reduce breeding success by limiting the food supply. Swallows produce multiple broods within a single season, with some species raising two or even three clutches of young. This allows them to maximize their reproductive output during the favorable warmer months.
From Eggs to Fledglings
Swallows construct their cup-shaped nests primarily from mud pellets mixed with grass, plant fibers, and saliva. These structures are attached to vertical surfaces under overhangs, such as the eaves of buildings, inside barns, or beneath bridges. Some species, like cliff swallows, create enclosed gourd-shaped nests with a narrow entrance.
Female swallows lay between three and six eggs, one per day. These eggs are small, white with dark, reddish speckles. The incubation period for swallow eggs lasts about 13 to 17 days, with both parents sharing the responsibility, though the female incubates more frequently.
Once hatched, the young swallows are altricial, meaning they are blind, featherless, and helpless. Both parents feed the rapidly growing chicks a diet of insects. The nestling period lasts approximately 18 to 24 days until the young are ready to fledge, or leave the nest. Even after fledging, the young may return to the nest for several weeks for continued feeding and shelter before becoming fully independent.
Observing Nests Responsibly
Swallows and their nests receive protection under the Migratory Bird Treaty Act of 1918, a federal law that prohibits the disturbance or destruction of active nests, eggs, or birds without a permit. It is important to observe swallow nests from a respectful distance to avoid causing stress or abandonment.
If a swallow nest is found in an inconvenient location, such as near a doorway, intervention is only permitted if the nest is inactive and empty. Property owners wishing to deter nesting in specific areas can implement measures before the birds arrive in spring or during the very early stages of nest construction, provided no eggs or chicks are present. These preventative actions might include installing physical barriers like netting or smooth surfaces where mud cannot adhere. Removing old, empty nests from previous seasons can also discourage reuse.