Swallows are small, agile songbirds known for their speedy, swooping flight patterns. Many species of swallows are highly migratory, traveling long distances between their breeding and wintering grounds each year. The length of the nesting season for swallows depends on the specific species and geographic location.
The Basics of Swallow Nesting
In North America, there are eight species of swallows that commonly breed across the continent:
- Tree swallow
- Violet-green swallow
- Northern rough-winged swallow
- Bank swallow
- Cliff swallow
- Barn swallow
- Cave swallow
- Purple martin
Swallows build nests out of mud or grasses in protected sites including tree cavities, crevices in cliffs or human-made structures, and burrows in embankments or the ground. Most species are highly social, preferring to nest in large colonies ranging from a few to hundreds of pairs.
Swallows arrive back to their breeding grounds and begin nesting at different times depending on the species and location. However, peak nesting activity for most North American swallows occurs between April and August. Swallows produce one brood per year, with clutch sizes ranging from 3 to 7 eggs depending on species. The incubation period lasts 10 to 21 days, and nestlings fledge in 15 to 28 days after hatching.
Tree Swallow
The tree swallow is a widespread species found across Canada and the United States. Tree swallows are early spring arrivals, with males returning to nesting sites first beginning in late February in southern areas and mid-March to early April in northern regions. Females follow 1-2 weeks after the males.
Nest building begins shortly after arrival at the breeding grounds. The nesting season lasts from March through July across their range, with later nesting in northern areas. Tree swallows fledge their young 25-28 days after the eggs hatch, so most nestlings have left the nest by late July or early August at the latest.
Violet-green Swallow
The violet-green swallow is a western species found in mountainous areas from British Columbia and western Montana south to New Mexico and Arizona. Their migration and nesting chronology is similar to tree swallows. Males arrive at the breeding sites in mid-March to late April, with females showing up about 2 weeks later.
Nesting activity lasts from late April to July. Violet-green swallow nestlings fledge about 20 days after hatching, so most young have left the nest by late July or early August at the end of the breeding season.
Northern Rough-winged Swallow
The northern rough-winged swallow breeds across much of North America. They are one of the earliest swallows to arrive back to their breeding range, with males first appearing in late February and March in southern areas. Females arrive in early April.
Nest building begins shortly after arrival. The nesting season for this species lasts from March through July, spanning 4-5 months. Nestlings fledge about 17-24 days after hatching, with most young fledged by mid-July through early August across their range.
Bank Swallow
Bank swallows live near water across much of North America. They are a moderately early spring arrival, showing up at breeding areas beginning in early April in the south and mid-April to early May in the north.
Nesting activity lasts from late April through July. Bank swallow nestlings take about 16-25 days after hatching to fledge, so most have left the nest by late July or early August as the breeding season comes to an end.
Cliff Swallow
Cliff swallows construct gourd-shaped mud nests attached to vertical surfaces such as cliffs or buildings. They breed across much of western and central North America. These swallows arrive at breeding areas beginning in early April in the south and mid-April to early May further north.
Nest building commences shortly after arrival. The nesting season for cliff swallows lasts from April through July. Young cliff swallows take about 20 days after hatching to leave the nest, so most have fledged by late July or early August across their range.
Barn Swallow
The barn swallow is one of the most widespread and recognizable swallow species. They breed throughout North America in proximity to humans where they construct mud nests attached to man-made structures. Males begin returning to breeding areas in March or April, with females arriving shortly after.
Nesting gets underway soon after arrival. Barn swallows have an extended breeding season lasting from April or May through September. However, they often raise 2-3 broods per summer, so peak activity is from May through July in most regions. Young fledge about 19 days after hatching, so by late September the breeding season comes to an end.
Cave Swallow
Cave swallows live in central Texas and Mexico. Their breeding habitats are caves and rock shelters. Males arrive at nesting sites beginning in early March, followed by females in late March or April.
Cave swallows have a relatively condensed breeding season from April to June. The young fledge about 20 days after hatching, so most have left the nest by late June or early July.
Purple Martin
Purple martins are the largest species of swallow in North America. They are colonial cavity nesters that readily nest in human-provided nest boxes. Purple martins begin arriving at breeding colonies in February in the southernmost parts of their range, late February to March in the south, and April through May in northern areas.
Males arrive first to scout out nesting sites, followed shortly by females. Nesting gets underway quickly and lasts from March through August, spanning 5-6 months. However, purple martins often raise multiple broods. Young fledge about 26-32 days after hatching, so most nestlings have fledged by late August as the breeding season comes to a close.
Summary of Swallow Nesting Season Length
To summarize, most swallow species have a peak breeding period that lasts 4-5 months on average. However, the exact timing varies by location and species. The table below shows the approximate nesting season duration for common North American swallows by region:
Species | Nesting Season Duration |
---|---|
Tree swallow | March – July |
Violet-green swallow | April – July |
Northern rough-winged swallow | March – July |
Bank swallow | April – July |
Cliff swallow | April – July |
Barn swallow | April – September |
Cave swallow | April – June |
Purple martin | March – August |
The earliest nesters tend to be species like northern rough-winged swallow and purple martin that arrive back to breeding areas early in spring. Late-season nesters include species like barn swallow that often raise multiple broods in a season. But overall, the core breeding season for most swallows lasts 4-5 months from April through July or August in most parts of North America.
Factors Influencing Nesting Season Length
Several factors can influence the exact timing and duration of swallow nesting seasons:
- Location: Swallows nest earlier in southern regions and later in northern areas.
- Spring arrival time: Species that arrive earlier generally start nesting sooner.
- Elevation: At higher elevations nesting is delayed compared to lower elevations.
- Climate: Warm springs with earlier insect emergence may allow earlier nesting.
- Experience: Older, more experienced swallows often nest earlier than younger birds.
- Weather: Severe weather like late cold snaps can delay the start of nesting.
- Food availability: Peak breeding is timed with maximum insect prey abundance.
- Number of broods: Swallows producing multiple broods nest for longer periods.
So while the core breeding season is April to August for most swallows, local and year-to-year variations can shift the precise nesting period by several weeks in some areas.
Nesting Site Preparation
Swallows prepare their nesting sites in various ways depending on species:
- Cavity nesters like tree swallows compete for natural tree cavities or nest boxes.
- Bank nesters like bank swallows dig fresh burrows each year in eroding banks or cliffs.
- Mud nesters like cliff swallows construct new gourd-shaped mud nests on vertical surfaces annually.
- Colony nesters like purple martins may repair and reuse old nests in colonies.
Nest preparation is part of the overall breeding timeline. It may take swallows between several days to a few weeks to construct or acquire their nests before egg laying can commence.
Nest Building and Egg Laying
Most swallow species begin building nests almost immediately upon arrival at their breeding areas, especially for cavity and burrow nesting species that must claim limited nesting spots early. Mud nest builders like barn swallows and cliff swallows construct new nests each year.
Swallows are highly social and nest in dense colonies from a few to hundreds of pairs. Both males and females participate in nest construction. Egg laying usually begins shortly after nests are complete, often within a few days.
Clutch sizes range from around 3 to 7 eggs depending on species. Swallows lay one egg per day until the clutch is complete. Some species like barn swallows will often produce 2-3 clutches in a breeding season.
Incubation
Incubation starts immediately after the last egg is laid. For most swallow species, females perform the majority of incubation duties. Incubation lasts between 10-21 days depending on the species:
- Tree swallow: 13-16 days
- Bank swallow: 12-15 days
- Cliff swallow: 12-14 days
- Barn swallow: 13-17 days
- Purple martin: 15-18 days
Both parents may help feed incubating females. Colder weather can slightly lengthen incubation, while very hot weather can shorten it by a few days.
Nestling Phase
Swallow hatchlings are altricial, meaning they are blind, featherless, and helpless at birth. They require intensive parental care for warmth and frequent feedings. Nestlings are brooded by the female for up to several days after hatching.
As they grow, both parents deliver food frequently, up to several hundred times per day. Nestlings develop quickly, growing feathers and increasing in size. At around two weeks of age, they are alert and active in nests.
The nestling phase lasts between 15 to 28 days depending on the species. By the end, nestlings are nearly adult size and ready to take their first flights.
Fledging
Fledging is the phase when young swallows take their first flights out of the nest. It is a quick process, often occurring within 1-3 days for an entire nest. Fledging for North American swallows happens at the following ages:
- Tree swallow: 18-25 days
- Bank swallow: 16-25 days
- Cliff swallow: 23-27 days
- Barn swallow: 19-23 days
- Purple martin: 26-32 days
Parents continue tending to fledglings for several days after leaving the nest, feeding them while teaching them to fly and forage.
Late Nesting Attempts
Some swallow pairs, especially barn and purple martins, may attempt to raise a second or even third clutch after successfully fledging an early brood. However, there is less time for late nest attempts to finish before autumn migration begins.
Pairs may lay smaller late clutches and young have less time to master flying and feeding skills. Late nests are also more prone to predation and abandonment if bad weather arises.
So while late nesting attempts occur, the earlier nestings result in the most success for swallows to breed and fledge young each season.
Conclusion
In summary, the nesting season for most species of North American swallows spans 4-5 months from April to July or August. However, factors like location, climate, food availability, and number of broods influence the precise start and end dates annually.
Swallows follow a synchronized breeding cycle of nest building, egg laying, incubating, brooding nestlings, and fledging young. Timing each stage correctly with seasonal food abundance is key to reproductive success.
While late nesting attempts can occur, early nestings coincide best with peak insect populations to allow swallows to raise healthy young. So the core swallow nesting season is concentrated in the April through August period across most regions.