Tree Swallows are small, migratory songbirds that breed across much of North America. They get their name from their habit of making nests in the hollows of trees. Tree Swallows arrive at their breeding grounds and begin nesting in the spring and summer months. The exact timing of nesting can vary across their range, but generally occurs between April and July.
What are the nesting requirements for Tree Swallows?
Tree Swallows nest in cavities, preferring natural tree hollows near open fields or water. They also readily nest in artificial nest boxes put up for them. Tree Swallows compete for the available nesting sites and are considered a semi-colonial species, with nests often located in loose groups or clusters. The nest is built by the female and consists of grasses and other plant materials lined with feathers. Tree Swallows feed extensively on flying insects and require abundant insect populations nearby to successfully raise their young.
When do Tree Swallows arrive at the breeding grounds?
Tree Swallows winter in the southern United States, Mexico, Central America, and the Caribbean. They migrate north to their breeding ranges beginning in late February and March. The exact arrival date can vary by location and weather conditions. In general, Tree Swallows arrive in the southern parts of their range by early March. They reach the northern parts of their range by mid-May. Males tend to arrive before females on the breeding grounds.
When does nest building begin?
Tree Swallows often begin nest site selection and nest building within a few days after arriving at the breeding grounds. Females assess potential nesting cavities and construct the nest. Nest building may begin in late March in southern areas and late April in more northern areas. Tree Swallows vigorously defend their nest sites from competing Tree Swallows during the nest site selection process. Nest building continues through completion of the nest which takes 1-2 weeks. Nests may be reused for subsequent broods or in following years.
When are eggs laid and incubated?
Once the nest is complete, the female lays a clutch of 4-7 white eggs. She will lay one egg per day. Egg laying may begin in early April in the south and mid-May in the north. The female alone incubates the eggs. Incubation lasts for approximately 14-15 days before the eggs hatch. The male will stand guard near the nest site and provide food to the female during incubation.
Timing of Nesting Stages
Here is a more detailed overview of the timing of the nesting cycle for Tree Swallows across their breeding range:
Southern Breeding Range
Arrival on breeding grounds | Late February – Early March |
Nest building | Late March – Early April |
Egg laying | Early April – Mid April |
Incubation | Mid April – Late April |
Hatching | Late April – Early May |
Fledging | Late May – Early June |
Northern Breeding Range
Arrival on breeding grounds | Mid May |
Nest building | Late May |
Egg laying | Late May – Early June |
Incubation | Early June – Mid June |
Hatching | Mid June – Late June |
Fledging | Late July – Mid August |
As shown, timing of nesting activities differs by up to 2 months between southern and northern parts of Tree Swallow’s breeding range. Generally, nesting occurs earlier in the south and later in the north.
Stages of the Nesting Cycle
Now let’s take a more detailed look at each stage of the Tree Swallow nesting cycle:
Arrival on the Breeding Grounds
– Tree Swallows migrate north to their breeding grounds in spring, with males arriving before females.
– Arrival occurs February to March in the south and May in the north.
– Adverse weather like cold temperatures or storms may delay arrival in some years.
– Males scout for nest sites and attract a mate upon arrival.
Nest Site Selection
– Females assess cavities for nest suitability based on dimensions, height above ground, etc.
– Nest sites are often reused from previous years.
– Tree Swallows vigorously defend potential nest sites.
– Nest boxes are readily accepted if located appropriately.
– Nest spacing ranges from 5 to 60 meters apart depending on habitat.
Nest Building
– Nest building is done primarily by the female.
– Nests consist of grasses and other plant materials.
– Feathers and fur are added to line the nest interior.
– Nest building may take 1-2 weeks to fully complete.
– Nest dimensions average 1.5 inches deep and 5 inches across.
Egg Laying
– Clutch size ranges from 4-7 white eggs.
– Eggs are laid at a rate of one per day.
– Laying starts 1-7 days after nest completion.
– Egg laying takes 4-7 days to complete.
– Some eggs may be laid in other nests (brood parasitism).
Incubation
– Only females incubate the eggs.
– Males stand guard and bring food to the incubating female.
– Incubation lasts for 14-15 days.
– Eggs hatch synchronously after 13-16 days.
– Hatching may take up to 2 days for all young to emerge.
Nestling Phase
– Both parents feed the nestlings small insects for about 18-22 days.
– Nestlings are brooded for about 7 days until well feathered.
– Feathers develop enough for flight at 16-25 days.
– Young leave the nest at ~22 days after hatching.
Fledging
– Fledging is the stage when the young leave the nest.
– Juveniles can fly moderately well at fledging.
– Parents continue to care for fledglings for 2-3 weeks.
– Juveniles become independent at 4-5 weeks of age.
Second Broods
– Tree Swallows frequently raise a second brood in a season.
– The second clutch may be laid in the same nest or a new nest.
– Timing is late May through July depending on latitude.
– Second broods are smaller with 3-5 eggs.
Factors Influencing Nesting Timeline
Many factors can influence the exact timing of nesting in Tree Swallows during the breeding season:
Weather
– Cold temperatures or severe storms during spring migration can delay arrival on breeding grounds.
– Wet, cold weather can delay nest building and egg laying activities.
– Hot, dry weather may cause premature fledging.
Food Availability
– Abundant insects allow for quicker egg laying and larger clutch sizes.
– Scarce food resources may delay breeding or reduce reproductive success.
Nest Site Competition
– More competition for nest sites may hurry mating and egg laying.
– Lack of optimal cavities may delay nest site selection.
Age and Experience
– Younger, inexperienced breeders tend to nest later.
– Older pairs and previous nesters start nests earlier.
Latitude
– More southern birds nest earlier than northern birds.
– Nesting in the north is delayed by colder temperatures.
Elevation
– Tree Swallows at higher elevations nest later due to colder and wetter conditions.
– Birds follow the snowmelt and emerging insects uphill during season.
Predation and Parasitism
– Failed first nests may force birds to attempt a late season re-nesting.
– Brood parasites like chickadees may delay Tree Swallow nesting.
How does nesting time influence reproductive success?
The timing of nesting during the breeding season has an important influence on the reproductive success of Tree Swallows. Early nesting is associated with greater breeding success.
Benefits of early nesting
– First nestings have higher egg and hatchling survival rates.
– Chicks from early broods have longer pre-fledging periods.
– Early nesters have more time to raise multiple broods.
– Greater insect food availability earlier in summer.
– Longer frost-free period for early nestlings.
Costs of late nesting
– Fewer prime nest sites available later in season.
– Declining insect food supplies as summer progresses.
– Hotter weather can cause premature fledging of chicks.
– Higher parasite loads in nests later in summer.
– Reduced time for successfully raising multiple broods.
Second Broods
– Second nestings allow pairs to maximize seasonal reproductive success.
– Second broods are smaller but augment population growth.
– Late second broods may not survive if hit by bad weather or food shortages.
Regional Variation in Nesting Timeline
Tree Swallow nesting timelines can vary across different regions within their breeding range. Here are some patterns of geographic variation:
Northern Populations
– Nesting runs from late May through early August.
– Shorter and more intensive breeding season.
– Second broods are less common or absent.
– Higher latitude birds migrate earlier to winter grounds.
Southern Populations
– Nesting may start as early as late March or April.
– Extended breeding season through summer.
– Higher frequency of double brooding.
– Later fall migration to wintering range.
Coastal Populations
– Moderate spring temperatures allow earlier breeding season.
– Coastal insects emerge earlier fueling egg production.
– Coastal climates extend the nesting season longer.
Inland Populations
– Colder spring weather delays breeding activities.
– Later spike in insect populations.
– Hotter, drier summers end nesting sooner.
Higher Elevations
– Slower spring green-up holds back breeding.
– Shorter frost-free period for raising young.
– Reduced re-nesting and second broods.
– Quick downslope fall migration.
Conclusion
In summary, Tree Swallows nest during the spring and summer months across North America. Nesting activities begin earlier in southern latitudes in April and progress later into May and June in the northern parts of their range. The nesting timeline follows stages of spring migration, nest building, egg laying, incubation, hatching, and fledging of the young. Tree Swallows frequently raise second broods later in the summer after successfully fledging their first brood.
Timing of nesting is influenced by weather conditions, food availability, nest site competition, and the age and experience of breeding birds. Early nesting pairs tend to have higher reproductive success. Geographical variation in factors like climate, season length, and food resources leads to regional differences in nesting timelines. Understanding the nesting requirements and behavior of Tree Swallows provides key insights into their life history strategy and population ecology. Careful monitoring of nesting phenology and success can serve as an important indicator of environmental conditions across North America.