Tree swallows are small, migratory birds that breed across North America. They are known for making nests out of mud which they attach to vertical surfaces. Tree swallow nests are unique in that they often have a very long entrance tunnel compared to other bird species.
What materials do tree swallows use to build nests?
The primary material used by tree swallows to construct their nests is mud. Specifically, tree swallows collect mouthfuls of wet mud near sources of water such as rivers, streams, ponds and lakes. They carry the mud back to the nest site and begin shaping it into a cup using their beaks and bodies to mold the structure.
In addition to mud, tree swallows may also incorporate other materials into their nests such as:
- Grasses
- Feathers
- Fine twigs
- Rootlets
These supplementary materials are woven into the basic mud structure. Grass and feathers may provide insulation while twigs and rootlets act as reinforcement to strengthen the nest walls.
Where do tree swallows build their nests?
Tree swallows build their nests in a variety of natural and man-made structures. Their preferred nesting sites include:
- Tree cavities
- Nest boxes
- Creek banks
- Rock crevices
- Cliff faces
- Building eaves
- Porch railings
The key requirements seem to be a vertical surface, preferably overlooking an open area, that provides shelter from predators and extreme weather. Tree swallows may compete with other cavity nesting birds for prime nesting real estate.
Why do tree swallow nests have long entrance tunnels?
The long, tunnel-like entrances on many tree swallow nests serve multiple purposes:
- Predator protection – The tunnels make it difficult for predators like raccoons, cats and snakes to reach in and grab eggs and nestlings.
- Stable temperature – The tunnels help regulate temperatures within the nest during hot summer days or cold snaps.
- All weather access – The tunnels allow the adult swallows to enter and exit the nest during rain or high winds.
Experiments where researchers trimmed back nest entrance tunnels showed reduced nesting success, demonstrating the importance of the tunnel design.
When do tree swallows build their nests?
Tree swallow nest building happens in the springtime leading up to egg laying. The general nesting timeline is:
- Late March to April – Females arrive at breeding sites first and begin nest construction.
- Early to mid May – Males arrive and pairing occurs. Males assist with completion of nests.
- Late May to early June – Egg laying and incubation.
Tree swallows are migratory so they must build a new nest each spring. First-year females often arrive latest at breeding sites and have less time to build, which may negatively impact their nesting success.
How long does nest construction take?
Tree swallow pairs can complete a nest in just 5-7 days under ideal conditions. However, nest building may take 2 weeks or longer:
- Poor weather like cold temperatures or heavy rain can halt mud collection.
- Competition for quality nesting sites may force swallows to lay claim to a site early before completing the nest.
- Older males with previous nesting experience build more rapidly than young females.
Ongoing maintenance and renovations to existing nests prior to and during the nesting season add to the total construction time.
Do both male and female tree swallows build the nest?
Nest building duties are shared between the male and female tree swallows:
- Females take the lead in initial nest construction after arriving at the breeding grounds.
- Males assist with the completion of the nest cup and tunnel after pairing up with a female.
- Females perform the majority of nest maintenance during incubation.
- Males may bring additional nesting material but leave final shaping to the female.
Partnership in nest building helps ensure timely completion. Mates may cooperate more closely when nesting sites are scarce or weather conditions make building challenging.
Do tree swallows use old nests?
Tree swallows occasionally reuse old nests, but most often build a new nest each year. Factors that may lead swallows to reuse an old nest include:
- Availability and proximity to mud sources – Old nests may be reused if new mud is added.
- Cavity nest site competition – Returning to an old cavity is easier than claiming a new one.
- Harsh weather – Reusing a nest allows quicker egg laying under challenging spring conditions.
Females are more likely to reuse a nest box where they were previously successful. Some old nests may be too degraded or filled with parasites to be suitable for reuse.
Do tree swallows build multiple nests in a season?
It’s common for tree swallows to construct 2-3 nests per breeding season. Reasons for multiple nest building include:
- An early nest fails due to predation, weather or other causes.
- A first clutch of eggs fails to hatch successfully.
- The female lays a second clutch after a successful first brood.
Having multiple nests gives swallows more chances to reproduce if conditions allow. Surplus nests may also provide roosting spots for the adults and fledglings later in summer.
Conclusion
Tree swallows build intricate mud nests each spring using materials gathered from nearby wetlands. Ideal nesting sites have a long entrance tunnel and are attached to vertical surfaces that offer weather protection. While the female generally initiates construction, both sexes cooperate to complete nest building. Swallows may build multiple nests in a season to increase their reproductive success. Their specialized nest design and adaptation to nest boxes have allowed tree swallow populations to thrive across North America.
