Purple martins are a type of bird that travel in large flocks and congregate together in colonies during breeding season. But what exactly is the proper term for a group of purple martins? Let’s take a closer look at purple martin group terminology and behavior.
The Basics on Purple Martins
The purple martin (Progne subis) is the largest species of swallow in North America. They have glossy dark blue or purplish-black feathers that cover their entire body except for lighter underparts on the breast. Purple martins are a highly social and gregarious species that migrates in large flocks from their wintering grounds in South America to their breeding grounds across North America.
Purple martins are dependent on humans for nesting, roosting, and feeding. They nest colonially in artificial multi-compartment birdhouses or hollow gourds provided by “martin landlords.” Landlords maintains large martin housing complexes with appropriate predator guards to attract flocks of these birds. Martins have adapted over time to rely on human-supplied housing because they have lost most natural cavities for nesting.
Terminology for Groups of Purple Martins
There are several terms used to describe groups of purple martins:
- Colony – Purple martins nest in colonies, with multiple pairs nesting in close proximity to each other in a martin housing complex. The size of a colony can range from a few pairs to over a hundred pairs.
- Roost – Outside of the breeding season, purple martins gather in large communal roosts at night to sleep. These can contain thousands of birds.
- Scout – An individual purple martin that scout outs new nesting sites in advance of spring migration and arrival of the full colony.
- Flock – Purple martins migrate in large flocks between their breeding and wintering grounds. A flock in flight can number in the thousands.
- Raft – A group of purple martins resting together on wires, branches, or other perches is called a raft.
- Kettle – A kettle refers to a flock of purple martins circling and soaring high up in the sky, sometimes intermingling with other swallow species.
Fall Migration of Purple Martins
One of the most spectacular sights of purple martins occurs in late summer and fall as the birds prepare for their migration back to South America. Large premigratory roosts form, containing thousands to tens of thousands of martins that funnel in each night to sleep. The martins gather an hour before sunset and create an enormous swirling flock called a staging kettle as they maneuver and soar overhead before descending into the roost.
Some key facts about purple martin fall migration and roosting behavior:
- Peak migration occurs in August and September.
- Juveniles leave first, followed by adult females, and finally adult males.
- Premigratory roosts are located in areas with an abundance of flying insects to feed on.
- Wetlands, like over lakes or rivers, are a preferred roosting habitat.
- Reed beds and cattails provide shelter and isolation from predators.
- Roosts can number from 1,000 birds up to 200,000 or more martins.
- The constant chatter in the roost is deafening.
- Predators like merlins, peregrine falcons, and cooper’s hawks will hunt a roost.
The mass exodus of thousands of purple martins from a roost at dawn is an unforgettable sight for bird enthusiasts. The huge kettle circles upwards before splitting off in smaller groups to feed for the day before gathering again at night to roost.
Purple Martin Colony Sizes
During the breeding season, purple martins nest in colonies that can vary greatly in size:
- A small colony may have just a few pairs nesting in a single martin house.
- A moderate size colony may have 10-20 pairs.
- Large colonies may have 50-100 pairs or more.
- Mega-colonies exceeding 100 pairs are possible in houses with over 24 rooms.
Here is a table showing example colony sizes:
Colony Size | Number of Pairs |
---|---|
Small | 4-8 pairs |
Moderate | 10-20 pairs |
Large | 50-100 pairs |
Mega | 100+ pairs |
The limiting factor is the number of nesting cavities available in the landlord’s martin housing setup. Landlords with multiple large houses in close proximity can attract mega-colonies. But even a single 12-room house placed in an ideal location can attract a sizable colony.
Ideal Colony Sites
Characteristics of ideal purple martin colony sites include:
- Open surroundings with a clear flyway to housing
- Situated above damp ground or open water
- At least 30-60 feet from trees/buildings
- Predator guards installed on housing poles
- Close proximity to good feeding sites like wetlands
- Siting on a hillside or ridge to aid launching
Purple martins prefer colony sites with abundant flying insects to feed on, open surroundings for ease of flying, and a certain amount of isolation from predators and human disturbance. Careful site selection and housing placement is key for attractors large colonies.
Communications in Purple Martin Colonies
Purple martins have complex vocalizations and displays that facilitate communication between colony members:
- Dawn song – Males sing each morning to establish territory and attract females.
- Soft songs and gargles – Used between paired males and females.
- Chortles – Short melodic vocalizations to greet arrivals.
- Clicks – Made during flight as contact calls.
- Alarm calls – Harsh “skee” noises to signal danger.
- Bill snapping – Males snap bills during conflicts.
- Wing waving – Visual display to attract females and defend sites.
Vocal communication facilitates pairing up for nesting, defending against intruders, alarming about predators, and coordinating flock movements. The noisy social chatter creates a sense of bonded community.
Benefits of Colonial Nesting
Purple martins reap several key benefits from colonial breeding rather than solitary nesting:
- Lower rates of predation – More birds to share watch duty
- Greater feeding efficiency – Information sharing about food sources
- Better mate assessment – Comparison of multiple mates
- Microclimate help – Sharing shade and humidity
The critical disadvantage is increased competition for nest sites and mates. But the overall benefits of group living outweigh the costs for purple martins.
Threats to Purple Martin Colonies
Purple martin colonies face a variety of threats during the breeding season:
- Adverse weather – Extended cold/rainy periods reduce insect prey.
- Predators – Hawks, owls, snakes, raccoons rob nests.
- Parasites – Nest mites, fleas, blow fly larvae.
- Disease – West Nile Virus, protozoans.
- Housing shortages – Lack of cavities limits colonies.
- Toxic chemicals – Pesticides poison birds and prey.
Colony survival depends on having adequate housing sites as well as an abundance of flying insect prey within proximity. Landlords can help counter predators, parasites, and housing shortages with properly managed martin housing.
Declining Purple Martin Populations
Over the last few decades, purple martin populations have declined across parts of North America, especially in the east. Contributing factors include:
- Starvation from pesticide use eliminating aerial insects
- Increased competition for cavities from European starlings
- Lack of landlords providing housing
- Increased predation from expanding hawk populations
More education is needed to recruit new landlords to put up housing and help reverse the declines. Optimally siting housing, guarding against predators, and monitoring colony health are key stewardship tactics.
Conclusion
In summary, purple martins are highly social birds that aggregate in large colonies for breeding and roosting. A group of nesting martins is called a colony, while roosting or migrating martins are known as a roost, flock, raft, or kettle depending on context. Colony sizes can range from a few pairs to over 100 pairs in mega-colonies. Whatever the group number, purple martins exemplify the adaptive benefits of colonial living for vulnerable migratory species.