The violet-green swallow (Tachycineta thalassina) is a small North American songbird found primarily in western North America. These swallows are known for their bright plumage and aerial acrobatics. Violet-green swallows build nests each spring to raise their young before migrating south for the winter. Understanding the nesting habits of these birds can provide insights into their biology and conservation. This article will explore key questions around violet-green swallow nesting:
How long is the nesting period?
The violet-green swallow nesting period lasts from around late April or early May through July. The total length of the nesting season is approximately 2.5-3 months. Here is a breakdown of the nesting timeline:
– Late April/Early May: Birds arrive at breeding sites and begin nest construction.
– May: Egg laying and incubation. The incubation period lasts for 14-16 days.
– June: Nestlings hatch and are fed by parents in the nest for 18-25 days until fledging.
– June/July: Fledglings leave the nest and are cared for by parents while learning to fly and hunt. Fledging period lasts 3-4 weeks.
– July: Nesting duties wrap up and birds start migrating south.
So the active nesting period from nest building through fledging of young is about 8-10 weeks. However, the birds occupy their breeding sites for 2.5-3 months in total while they mate, lay eggs, raise hatchlings, and prepare to migrate.
How many broods do they have?
Violet-green swallows typically raise one brood per year. They may produce two broods on occasion, but single broods are most common.
Some key facts about violet-green swallow broods:
– Clutch Size: 4-7 eggs per clutch, usually 5-6 eggs.
– Broods per Year: Most often 1 brood, sometimes 2.
– Nesting Attempts: 1-2 per season. If first nest fails, may re-nest.
Raising a single brood each summer allows the swallows to conserve energy for their long migration and to time nesting with peak food availability. Multiple broods are rarer with this species compared to some other types of swallows.
How many times do they reuse/rebuild nests?
Violet-green swallows will often reuse the same nest over multiple years. Individual pairs may return to the same nesting site and renovate an existing nest. Nests that survive the winter are more likely to be reused than new nests.
Some key statistics on violet-green swallow nest reuse:
– 60-70% of nests are reuses of old nests, rather than new builds.
– In one study, 49% of nests were repaired and reused over consecutive years. The record was 5 years of reuse.
– Most reused nests receive fresh mud lining annually before eggs are laid.
– Nest reuse saves time and energy compared to building a completely new nest each year.
– Nest reuse is higher in tree cavity sites than artificial nest boxes. Cavities provide more protection from weather.
So while they may do some annual maintenance, a violet-green swallow pair often settles in the same nesting cavity or nest box for multiple seasons. This nest site fidelity contributes to reuse rates over 50% on average.
How many eggs do they lay each time?
Violet-green swallow clutches typically contain 4 to 7 eggs. The average clutch size is 5 to 6 eggs.
Here are some details on violet-green swallow clutch size:
– Average Clutch Size: 5-6 eggs
– Clutch Range: 4-7 eggs
– Largest Clutches: Occur in the middle of the nesting season
– Smallest Clutches: Earlier and later clutches often have fewer eggs
– Clutch Size Decreases: Clutches get smaller with each renesting attempt after a failure
– Egg Color: White with brown speckles
– Egg Dimensions: 18 x 13 mm, oval shaped
– Egg Laying: One per day until clutch complete
– Incubation: Starts after penultimate egg is laid
Having 5-6 eggs balances risks of predation and increased competition between hatchlings. The large clutches maximize reproductive success and account for potential egg losses.
How many times do they nest in a lifetime?
Violet-green swallows often nest over multiple seasons throughout their lifetime. The typical violet-green swallow may breed for 2-3 years. With an average lifespan of 2-4 years, most individuals nest for the majority of their adult lives.
Here are some details on lifetime nesting habits:
– Average Lifespan: 2-4 years
– Age at First Breeding: 1 year old
– Average Breeding Seasons: 2-3 years
– Longest Observed Lifespan: 11 years
– Longest Observed Breeding: 7 years
– % Returning to Same Site: 40-60% site fidelity
– Survival Rate: 50-65% annual survival of adults
With a relatively short life span, most violet-green swallows don’t actually live long enough to nested more than a few seasons. Those that do live longer maintain high site fidelity and may return to the same nest over multiple years. Their lifetime breeding success depends on survival rates to breed again each spring.
Nest Locations
Violet-green swallows nest in cavities, both natural and artificial. They are flexible in utilizing different nest sites across their range. Here are details on common violet-green swallow nest locations:
Tree Cavities
Dead and decaying trees provide natural cavities used by violet-green swallows. They nest in various tree species including:
– Aspen
– Cottonwood
– Oak
– Birch
– Conifers
Tree holes made by woodpeckers are also prime nest sites. Nest height ranges from 3 feet to over 60 feet off the ground.
Rock Crevices
Rocky cliffs, banks, and outcrops also offer cavities for nesting. These sites are more common at higher elevations and in rocky areas across the range.
Nest Boxes
Violet-green swallows readily use artificial nest boxes, including:
– Wooden boxes
– Metal/PVC pipe boxes
– Gourds
Boxes can be attached to trees, fence posts, or other structures. They should have a 1-1.5 inch diameter entrance hole placed 6-15 feet high.
Building Eaves
In urban and residential settings, violet-green swallows often nest under the eaves of buildings. They access small holes to build nests on the inside of the structure.
Bridges
Cavities on bridges provide protected nest sites over water. Swallows may access hollows through gaps in the infrastructure. Bridge sites are more common in portions of the coastal range.
Nest Availability
Nest site availability can limit populations in some areas more than food supply. Providing additional artificial nesting opportunities supports breeding.
Nest Construction
Violet-green swallow nests are cup-shaped structures built primarily from mud and grass. Here are some key facts about their nest construction process:
Nest Building Materials
– Mud: Collected from pond edges and wetlands. Forms main structure. Hardens like concrete.
– Grass: Woven into mud to strengthen walls.
– Feathers: Line interior for insulation.
– Other Materials: Moss, pine needles, leaves, animal hair.
Typical Dimensions
– Inside Diameter: 4-6 inches
– Inside Depth: 2-4 inches
– Wall Thickness: 1 inch
– Entrance Diameter: 1.5-2 inches
Construction Timeline
– 3-14 days: Varies based on weather, availability of mud, cavity depth.
– Mud Gathering: Females gather most mud themselves.
– Grass Addition: Males assist with grass weaving.
– Nest Reuse: Refurbish and relined annually.
Mud Gathering Adaptations
– Specially adapted feathers: Have fringe on feet to carry mud.
– Saliva: Helps bind mud into solid pellets.
– Behavior: Hover over mud and rub beak to collect.
Their unique adaptations allow violet-green swallows to construct durable nests from basic natural materials. Parent birds work together to build a secure home for their hatchlings.
Geographic Range
The geographic breeding and nesting range covers much of western North America. Here is a map and details:
Breeding Range
– Alaska: Central and southeast regions
– Canada: Yukon, British Columbia, Alberta
– Western U.S.: Washington, Oregon, California, Idaho, Montana, Wyoming, Colorado, Utah, Nevada
– Southwest: New Mexico, Arizona
– Midwest: Western Nebraska, Kansas
Migration
– Winters along Pacific Coast from British Columbia to Mexico. Also winters in southeast Arizona.
– Spring migration north from March to May.
– Fall migration from August to October.
Ideal Breeding Habitat
– Open woodlands and forests with cavities near water.
– Mountain meadows with cliff walls or riparian areas.
– Rural settings with barns, outbuildings, fences to provide nest sites.
Access to mud, insects, and nesting sites determines breeding range boundaries. Most nesting occurs relatively near their wintering grounds.
Feather Identification
The bright green and violet iridescent feathers of the violet-green swallow make it easily identifiable. Unique plumage differences help distinguish males and females.
Male Plumage
– Crown: Violet-blue
– Back: Dark iridescent green
– Rump: Same green as back
– Throat: White
– Belly: White
– Flanks: Grayish brown
– Tail: Dark brown, slightly forked
Female Plumage
– Crown: Gray
– Back: Duller green than male
– Rump: Gray
– Throat: White
– Belly: White
– Flanks: Grayish brown
– Tail: Dark brown, slightly forked
The males’ bright violet-blue crown is the best way to identify their gender. Females also lack the same iridescent green sheen on the back and rump. Juveniles resemble females until acquiring adult plumage after first year.
Nesting Behaviors
Violet-green swallows exhibit unique nesting behaviors and parenting roles. Here are key aspects of their breeding biology:
Social Nesting
– Colonial nesters: Nest in aggregations at some sites.
– Benefits: Grouping may provide protection from predators.
– Colony Size: Up to several hundred pairs documented.
– Nest Spacing: Often 2-15 feet apart depending on site.
– Not Always Colonial: Also nest as single isolated pairs.
Mating/Egg Laying
– Monogamous pairs: Mate for life, though will re-pair after death.
– Courtship: Aerial displays, male feeding female.
– Copulation: Typically occurs in or at nest.
– Egg laying: 1 per day, up to 7 days until complete.
Parenting Roles
– Incubation: By female only, male guards.
– Nestlings: Fed by both parents up to 500 times/day.
– Fledglings: Cared for by both parents 3-4 weeks.
Parents work together to give hatchlings the best chance of survival. Their partnerships continue season after season at familiar nest sites.
Diet
Violet-green swallows are insectivores, feeding on flies, mosquitoes, beetles and other aerial insects. Here are some details about their diet and foraging habits:
Primary Prey
– Flies (midges, crane flies, robber flies)
– Mosquitoes
– Bees and wasps
– Mayflies, dragonflies
– Flying beetles and other bugs
Foraging Strategy
– Aerial hunting: Catch insects mid-flight.
– Hawks and gleans: Catches stationary insects off surfaces.
– Usually forages 10-30 feet above ground.
– Requires open habitats with aerial insect populations.
Energy Requirements
– Adults consume 14 g of insects daily on average.
– Nestlings can eat over 1,000 insects per day.
– Parents make hundreds of foraging trips while feeding young.
Drinking
– Drinks by skimming low over water surface.
– Also catches emerging aquatic insects near water.
Access to prolific flying insect populations is key habitat requirement for these aerial insect hunters. Abundant spring through summer prey allows them to successfully raise young.
Migration
Violet-green swallows migrate annually between breeding and wintering grounds. Key facts about their migration:
Winter Range
– Pacific Coast from British Columbia to Mexico.
– Southeastern Arizona.
– Mild climates with insect prey availability.
Migration Distances
– Northern breeders: 5,000+ miles round trip.
– Southern breeders: 1,000+ miles round trip.
– Travel 30-60 miles per day.
Spring Return
– Males arrive at breeding sites first.
– Immature birds arrive later.
– Arrival dates range from March-May.
Fall Departure
– Females and young depart before adult males.
– Peak departure late August to early September.
– Stragglers remain until October.
Their migration strategies maximize survival and breeding opportunities across the range. Coordinated seasonal movements help connect distant nesting sites and winter habitats.
Conservation Status
Violet-green swallows have a large range but face threats from habitat loss and climate change. Their current conservation status:
Population Estimate
– North America: 18 million individuals
– Globally: 19 million
Population Trend
– Decreasing by 30-49% over the last 50 years across western North America according to Breeding Bird Survey.
Major Threats
– Habitat loss: Reduction in nest sites from development, loss of dead trees.
– Climate change: Impacts migration timing and prey populations.
– Introduced species: Compete for nest sites with non-natives.
– Pesticides: Exposure may reduce prey and reproduce mortality and deformities.
Conservation Status
– IUCN Red List: Least Concern
– Federal Protection: Migratory Bird Treaty Act
Targeted conservation action could support populations where habitat and climatic changes are resulting in declines. Continued monitoring is recommended.
Key Facts Summary
– Nesting period lasts 2.5-3 months from late April through July.
– Typically raise just 1 brood per year with 5-6 eggs.
– Reuse nests 50% of time, record is 5 years of reuse.
– Lay average clutch of 5-6 eggs over 7 days.
– Most breed for 2-3 of their 2-4 year lifespan.
– Nest in cavities in trees, rocks, buildings, and nest boxes.
– Build mud cup nests lined with grass and feathers.
– Breed across much of western North America.
– Males have bright violet-blue crowns, females are gray.
– Aerial insectivores that catch flies, mosquitoes, beetles.
– Migrate annually from western wintering grounds.
– Populations declining due to habitat loss and climate change.
Conclusion
Violet-green swallows have adapted specialized behaviors and traits to take advantage of seasonally abundant aerial insects across western North America. Their mud nest construction, aerial insect hunting, and long-distance migration showcase the species’ unique biology. Loss of critical breeding habitats and climate change impacts remain conservation concerns for maintaining stable violet-green swallow populations into the future. Ongoing research and monitoring of nesting ecology, reproduction, survival rates, and migration patterns are needed to fully understand population trends and inform management efforts for this iconic western aerial insectivore.
