Purple Martins are migratory birds that breed in North America during the spring and summer months. After mating, the female Purple Martin lays eggs and incubates them for about 15 days before they hatch. Once the chicks hatch, both parents work together to feed and care for the babies until they are old enough to leave the nest, or fledge. So how long do the baby Purple Martins stay in the nest before fledging?
Nestling Stage
After hatching, baby Purple Martins are completely dependent on their parents for food and protection. This stage, where the babies are confined to the nest, is called the nestling stage. Purple Martin chicks are altricial, meaning they hatch blind, naked, and helpless. Their eyes open around day 5 and they start growing feathers around day 7.
For the first week after hatching, the nestlings are brooded almost constantly by the female parent to keep them warm. The male parent brings food back to the nest which the female then feeds to the babies. As the chicks get older, both parents forage for insects to feed the growing nestlings.
Purple Martin chicks grow incredibly quickly in the nest. They can put on up to 1 inch in length and quadruple their hatching weight in a single week! By 2 weeks old, their flight feathers start growing in. At this point, the female parent stops brooding them continuously.
By the time they reach 3 weeks old, Purple Martin nestlings are quite large and fully feathered. They appear nearly ready to leave the nest, but they still depend completely on their parents to bring them all their food at this stage.
Feeding Behavior
The feeding behavior of the parents changes dramatically when the chicks are 3 weeks old. Up until this point, the parents brought food back to the nest frequently, sometimes feeding the babies over 400 times per day! But in the last week before fledging, the parents start making fewer feeding trips.
This forces the nestlings to stretch out the time between meals. The decreased feeding triggers the chicks’ instincts to start wandering out of the nest in preparation for fledging. By reducing the frequency of feedings, the parents are essentially coaching the babies to get ready to leave the nest and fly on their own.
Fledging Timeline
So when exactly do Purple Martin chicks finally fledge, or take their first flight? Most sources state that Purple Martins fledge about 4 weeks after hatching. However, the exact timing seems to depend on several factors.
Clutch Initiation Date
One factor that influences fledging time is timing of nest initiation. Purple Martins can raise up to 3 clutches per breeding season. Earlier clutches tend to fledge faster than later ones.
Data from a 5-year study of Purple Martins in Pennsylvania found:
- First clutch nestlings fledged at about 28 days old
- Second clutch nestlings fledged at about 30 days old
- Third clutch nestlings fledged at about 32 days old
So earlier clutches fledge a few days sooner than later clutches in the same season. This may be because parent birds are more energized early in summer, allowing them to provision the nestlings faster.
Weather Conditions
Weather conditions like temperature and rainfall also impact the fledging timeline. Colder temperatures or excessive rain can slow down nestling development. And if conditions are severe enough, they can even result in nest failures.
Hot, dry weather on the other hand may accelerate development and cause earlier fledging. A Louisiana study found that nestlings fledged about 1 day earlier for every 10 degree F increase in temperature.
Nest Height
Another factor is nest height. Purple Martin nests can be located from just a few feet off the ground up to over 100 feet high. Researchers have found that chicks in higher nests tend to fledge about 1 day later for every additional 33 feet in height.
This may be because the parents expend more energy flying up to higher nests with food for the chicks, so they end up feeding them less frequently. The decreased feeding then delays development slightly.
Colony Size
Finally, colony size seems to impact fledging age. Purple Martins nesting in larger colonies tend to fledge 1-2 days sooner than those in smaller, isolated colonies.
In large colonies, there is more competition between nestlings begging for food. This may pressure the parents to provision more frequently, speeding up development.
Leaving the Nest
So while 4 weeks is the general rule of thumb, the actual age at fledging can range from about 26 to 32 days depending on various conditions. No matter when they fledge, all Purple Martin chicks face the same dangerous challenge of taking their first flights.
The first flights are usually clumsy, short hops and flutterings near the nest. The fledglings improve quickly with practice and will continue begging their parents for food while mastering their flying skills.
For the first few days after leaving the nest, the fledglings remain close by, frequently returning to the nest or resting on nearby perches. But soon their flight abilities allow them to begin venturing further away.
By about 6-8 weeks after hatching, the juveniles are adept fliers and ready to migrate south with their parents. Amazingly, just a month and a half earlier they were helpless hatchlings confined to the nest.
Typical Purple Martin Fledging Timeline:
- Hatch from eggs – Day 0
- Eyes open – Day 5
- Feathers begin growing – Day 7
- Nestling stage ends – Day 28-32
- Fledge from nest – Day 28-32
- Improve flying skills near nest – Day 28-35
- Venture further from nest – Day 35-42
- Capable of sustained flight – Day 42-50
Comparison to Other Bird Species
Purple Martins have one of the longest nestling periods of any North American songbird. Here’s how their fledging timeline compares to some other species:
Species | Fledging Age |
---|---|
Chimney Swift | 28 days |
Purple Martin | 28-32 days |
Cliff Swallow | 23 days |
Carolina Chickadee | 16-17 days |
Tufted Titmouse | 15-16 days |
House Wren | 14-15 days |
The longer nesting period of Purple Martins compared to other cavity nesters may be related to their diet. Purple Martins feed their young a high proportion of dragonflies and other large insects. These take longer to provision compared to smaller prey items.
The extended nestling phase allows the chicks time to grow strong flight muscles to handle such large prey. It also enables them to learn the highly coordinated aerial maneuvers that make Purple Martins such skillful fliers.
Fledgling Mortality
The fledging period is one of the most hazardous times in a Purple Martin’s life. One study estimated mortality rates as high as 70% for Purple Martins in the month after fledging.
Their still-developing flying skills make fledglings vulnerable. Collisions with trees, buildings, vehicles, and other structures take a heavy toll. Fledglings are also easier targets for aerial predators like hawks and falcons.
Harsh weather is another major threat. Extended cold, heat, rain or wind can be deadly for fledglings still learning to fly and feed themselves. Fledglings also sometimes starve as they adjust from being fed by parents to self-feeding.
If the juveniles can make it through the flight training period, their chances of survival greatly improve. But the month after leaving the nest remains a precarious time.
Helping Fledglings Survive
Here are some ways people can help fledgling Purple Martins and other migratory songbirds survive this vulnerable stage:
- Avoid trimming trees and bushes near nests during fledging season
- Keep pets indoors so they don’t disturb fledglings
- Drive carefully and watch for fledglings on roads
- Keep yard areas safe by removing hazards like ponds or wires
- Reduce or eliminate pesticide use which reduces insects for feeding
- Keep nests sites and bird baths clean to prevent disease
- Plant native flowers and shrubs that attract insect prey
Conclusion
Most Purple Martin chicks fledge when they are between 28 to 32 days old. However, factors like weather, nest height, and colony size can shift the timeline by a few days in either direction. Fledging is a precarious stage, but the parents help the juveniles gain flight skills, independence, and survival abilities.
With some assistance from people during this vulnerable period, many fledglings are able to overcome the odds and live on to make their first migration south.