Fledgling birds are young birds that have developed enough to leave the nest, but are still dependent on their parents for food and protection as they learn to fly. The fledgling stage is one of the most vulnerable times in a bird’s life, as the young birds must face predators, starvation, and other threats without the complete protection of a nest or their parents’ constant care. However, with some luck and the right conditions, many fledglings do manage to survive this precarious stage and go on to adulthood.
How long does the fledgling stage last?
The fledgling stage lasts anywhere from a few days to a few weeks after a chick leaves the nest. The length of time spent as a fledgling depends on the species. For example, American robins only spend about 4-5 days as fledglings before they are competent fliers and can fly reasonably well. On the other hand, albatross chicks may wander from the nest before they can even fly, and take several months to fully fledge.
During the fledgling period, the young birds are learning critical survival skills such as flying, finding food, avoiding predators, and orienting themselves in their environment. At first fledglings are very vulnerable because their flight skills are poor, they begging calls draw attention, and they do not know how to find food on their own. Parents must show them where to find food and shadow them to protect them. Over time the young birds get stronger, more adept at flying and catching prey, and better at hiding from predators. Once they can survive independently from their parents, the fledgling phase ends.
What are the threats faced by fledgling birds?
Newly fledged birds face a number of threats in their environment including:
- Starvation – Fledglings do not know how to find food on their own and require their parents to feed them frequently. They can starve if parents cannot find enough food for the brood.
- Predators – Young fledglings may be caught by predators like cats, snakes, and raptors since they cannot fly quickly or well. Their begging calls also attract predators.
- Collisions – Young birds sometimes collide into manmade objects like windows or wires because their flight skills are poor.
- Falls – Fledglings can fall from their perches before they can fly well, especially in gusty or poor weather.
- Harsh weather – Extended bad weather or storms can make it hard for parents to find food and can cause direct mortality.
- Nest parasites and diseases – Leftover parasites from the nest may continue to weaken young birds, or they may contract diseases from parents.
In addition to these direct mortality risks, most fledglings probably die from a combination of starvation and exposure. Without adequate food and parental care, they quickly weaken, lose body condition, and become more vulnerable to predation or accidents.
How do parent birds care for fledglings?
Parent birds play a critical role in helping their fledglings survive:
- Feeding – Parents work from dawn to dusk capture food to bring back to fledglings. They may feed young 6-12 times per hour!
- Leading – Parents call and lure young birds to good foraging sites with abundant prey.
- Teaching – Parents demonstrate hunting skills and teach fledglings step-by-step how to capture prey.
- Guarding – Parents stay alert and guard young birds against potential predators and threats.
- Sheltering – Parents lead fledglings back to the nest or a sheltered site to rest at night and during bad weather.
Even after leaving the nest, fledglings rely almost entirely on their parents for survival. However, parents must balance caring for existing young with guarding resources for future nesting attempts. This tradeoff influences how much care they can provide.
What adaptations help fledgling birds survive?
Fledgling birds have several behavioral and physical adaptations to help them through the fledgling period including:
- Begging calls – Loud, incessant calling stimulates parents to feed them frequently.
- Gaping mouths – Bright mouths help guide parents to deliver food.
- Cowering – Fledglings freeze or hide in vegetation when scared to avoid predators.
- Cryptic plumage – Their drab juvenile feathers help camouflage young birds in vegetation.
- Early flight – Many species fledge before they can fly well to escape ground predators.
- Rapid growth – Birds develop quickly and can double their hatching weight in just a few days.
These adaptations allow fledglings to maximize calories from their parents while avoiding threats just long enough to develop into adept juveniles. However, even with these adaptations, mortality at this stage remains extremely high.
How can you help fledgling birds survive?
Here are some tips for helping fledgling birds you find:
- Leave them be – Moving healthy fledglings is illegal. Parents are likely still feeding them.
- Monitor from a distance – Watch for signs of distress or parents returning.
- Avoid domestic pets – Keep cats indoors and dogs leashed and away from the bird.
- Create cover – Place some leafy branches or a cardboard box near the bird for shelter.
- Remove dangers – Ensure the bird is not near streets or high ledges.
- Contact a rehabber – If parents do not return or the bird is clearly injured or ill, call a wildlife rehabilitator.
With quick action and care, even downed fledglings can often recover and be returned to their parents successfully.
What percentage of fledglings survive to adulthood?
Survival rates during the fledgling stage can vary dramatically based on the species, habitat, availability of food, and population of predators. Exact data is limited, but some examples of fledgling survival rates include:
- Song sparrows – Estimated only 25-30% survive to independence.
- Wood thrushes – Up to 70% mortality has been observed in the month after fledging.
- Whooping cranes – In some years almost no fledglings survive their first migration.
- Chimney swifts – Have around 50% survival in the 3-4 week fledgling period.
- Roseate terns – Approximately 40% of fledged chicks survive to fly to wintering grounds.
Across most species, mortality ranges from 50-70% during the fledgling phase. However, even birds that become independent juveniles have low odds – for example, a young robin reaching adulthood may represent just 4% of its original clutch. The high mortality ensures steady population turnover and allows the strongest individuals to reproduce.
How do predators impact fledgling survival?
Predators are one of the largest threats to fledgling birds that are naive, cannot fly well, and advertise their presence with loud begging. Some major groups of fledgling predators include:
Mammals
- Cats – Domestic and feral cats kill billions of birds each year. Nests and fledglings are easy targets.
- Raccoons – These omnivorous scavengers readily climb trees to reach nests and are common urban predators.
- Foxes – Foxes grab unattended fledglings from shrubbery. Some leap or dig into nests.
- Rodents – Rats, mice, chipmunks, and squirrels may eat eggs and nestlings.
Birds
- Raptors – Hawks, falcons, owls, and eagles prey on fledglings of other species.
- Crows – Very intelligent, these birds watch for parent activity then raid nests.
- Jays – Jays take eggs and young birds when parents are away.
- Herons – Herons eat small fledglings and juveniles.
Reptiles & Amphibians
- Snakes – Snakes raid nests in trees, shrubs, and on the ground and consume eggs and young.
- Lizards – Some climbing lizards will take small eggs and nestlings.
- Frogs & Toads – These opportunists consume nestlings and small fledglings.
In addition to directly preying on fledglings, the constant threat of predation may prevent parent birds from properly caring for their young, indirectly impacting the fledglings’ survival.
What effects do fledgling mortality rates have on bird populations?
The high mortality of fledglings has several important effects on overall bird populations:
- Fledgling mortality sets the ceiling for maximum population growth. Only a fraction of hatchlings survive to reproduce.
- High mortality winnows out weaker individuals and allows strong birds to thrive.
- Mortality clears space in the habitat for new birds to nest in future years.
- It prevents successful breeders from dominating prime nest sites year after year.
- Population numbers are kept in check so food resources are not depleted.
While the mortality seems harsh, it is a natural and essential part of balancing bird populations. However, extremely high predation, habitat loss, or other human-caused impacts can negatively affect fecundity.
Conclusion
The fledgling stage is the most perilous, yet vital period in a young bird’s life. While fledglings face daunting odds, their high mortality rate ultimately strengthens populations by ensuring turnover, healthy competition, and availability of resources for future generations. Supporting fledglings through habitat protection, reduction of predators, and responsible policy is key to maintaining abundant and resilient bird populations.
