During the fourth week after hatching, peregrine falcon chicks (eyases) continue to undergo significant changes in preparation for fledging.

Day 22-24:

– Feather Development: By now, the chicks have a substantial amount of juvenile feathers, especially on their wings and back. The down feathers are mostly replaced by these juvenile feathers, which are darker and more streamlined.
– Weight and Size: The chicks continue to grow, with their weight reaching between 500-800 grams (18-28 ounces). Females are typically larger than males.
– Preening: Preening becomes more frequent as they take care of their feathers. This behavior helps ensure their feathers are in good condition for future flight.

Day 25-27:

– Wing Exercises: The chicks engage in vigorous wing flapping to strengthen their muscles. They may even start to lift slightly off the ground, practicing for their first flight.
– Mobility: Their movements become more coordinated and confident. They explore the nest area more thoroughly, hopping and walking around.
– Feeding: The parents continue to bring food, but the chicks may start to eat more independently. They can tear apart small pieces of meat on their own, though they still rely on their parents for larger prey.

Day 28:

– Social Interactions: Interactions with siblings become more complex and frequent. They engage in playful mock battles and other social behaviors that help them develop their hunting and survival skills.
– Vocalizations: The chicks’ vocalizations become more varied and sophisticated. They communicate more effectively with their parents and siblings.
– Independence: While still dependent on their parents for food, the chicks show increasing signs of independence. They may start to watch the sky more intently, observing their parents’ hunting and flying techniques.

Overall Development During the Fourth Week:

The fourth week is a crucial period for peregrine falcon chicks as they prepare for fledging. The significant growth in their feathers and the development of their muscles and coordination are essential for their first flight. The chicks’ increasing independence and social interactions also play a vital role in their preparation for life outside the nest. The parents continue to provide food and protection, but the chicks’ growing autonomy signals their readiness to leave the nest soon.

During the third week after hatching, peregrine falcon chicks (eyases) continue to experience significant physical and behavioral development.

Day 15-17:

Feather Development: The down feathers are gradually replaced by darker juvenile feathers, especially on the wings and back. These juvenile feathers are more streamlined and will eventually aid in flight.

Increased Size: The chicks continue to grow rapidly, with their weight now ranging between 250-400 grams (9-14 ounces). Their bodies become more robust, and their legs and feet grow stronger.

Hunger: Their appetite remains voracious, requiring the parents to provide a steady supply of food. The tiercel (male) continues to hunt frequently, bringing back prey which the falcon (female) helps to feed to the eyases.

Day 18-20:

Mobility and Coordination: The chicks’ movements become more coordinated. They start to stand on their feet more reliably and may take short, wobbly steps around the nest. This increased mobility helps them exercise their growing muscles.

Preening and Wing Flapping: They begin to preen more frequently, taking care of their developing feathers. Wing flapping becomes more common as they start to build the strength necessary for flight. These flapping exercises are crucial for developing their pectoral muscles.

Social Behavior: Interactions between siblings become more complex. They may engage in mock battles, which help them develop hunting and defensive skills. These playful activities are essential for learning social hierarchies and improving coordination.

Day 21:

Further Feather Development: By the end of the third week, the chicks have a noticeable amount of juvenile feathers. They still retain some of their down, but the sleek, darker feathers are becoming more prominent.

Weight and Size:Their weight continues to increase, with females generally larger than males. By now, the chicks weigh between 350-550 grams (12-19 ounces).

Vocalizations: Vocal communication becomes more sophisticated. The chicks use a variety of calls to communicate with their parents and each other, often demanding food with loud, persistent cries.

Independence: While still heavily reliant on their parents, the eyases begin to show more signs of independence. They explore their immediate environment more confidently, occasionally venturing to the edge of the nest.

Overall Development During the Third Week:

The third week is a period of intense growth and physical development for peregrine falcon chicks. Their transformation from fluffy, down-covered eyases to more sleek, feathered juveniles is well underway. The increased mobility, coordination, and strength they develop during this period are critical for their upcoming stages of development, particularly as they prepare for fledging. The parents continue to play a vital role in providing food and protection, but the chicks’ increasing independence and curiosity signal their gradual transition toward self-sufficiency.

The growth and development of peregrine falcon chicks during the first two weeks after hatching are rapid and fascinating. Here’s a detailed overview:

First Week (Days 1-7)

Day 1-2:
– Hatching:The chicks, known as eyases, hatch after about 33-35 days of incubation. They emerge from their eggs with the help of an egg tooth, a small, temporary structure used to break the shell.
– Appearance: They are covered in white down feathers and have closed eyes. They are very small and weigh around 35 grams (about 1.2 ounces).
– Dependence: The eyases are highly dependent on their parents for warmth, protection, and food. The female, known as the falcon, broods them almost continuously to keep them warm, while the male, known as the tiercel, hunts and brings food.

Day 3-4:
– Feeding:The parents begin feeding the chicks small pieces of meat, often several times a day. The falcon tears food into tiny, manageable pieces to feed the eyases.
– Growth: The chicks start to gain weight rapidly, approximately doubling their birth weight by the end of the first week. Their digestive systems are efficient, and they produce a lot of waste, which is removed by the parents to keep the nest clean.

Day 5-7:
– Eyes Opening: By the end of the first week, the chicks’ eyes start to open. Their vision, initially limited, begins to improve, allowing them to start recognizing their surroundings and parents.
– Mobility: The eyases become more active and begin to move around the nest, though their movements are still quite clumsy.
– **Vocalization:** They start to make more vocalizations, calling out for food and interacting with their siblings and parents.

Second Week (Days 8-14)

Day 8-10:
– Feather Development: The down feathers begin to grow thicker, providing better insulation. The chicks still rely heavily on their parents for warmth, but can tolerate short periods without brooding.
– Appetite: Their appetite continues to increase, and the parents must hunt frequently to provide enough food. The tiercel often brings prey to the nest several times a day.
– Weight Gain: By the end of the second week, the chicks’ weight continues to increase rapidly, reaching around 150-250 grams (5-9 ounces), depending on food availability and individual variation.

Day 11-14:
– Further Development: The chicks’ eyes are fully open, and their vision sharpens. They become more coordinated and start to practice using their talons and beaks, essential skills for later life.
– Social Interaction: The eyases interact more with each other, sometimes engaging in playful tussles. These interactions are important for developing their social and physical skills.
– Independence: They begin to show brief signs of independence, such as preening themselves and exploring the nest area more actively. However, they are still completely reliant on their parents for food and protection.

Overall Growth and Development:
During the first two weeks, peregrine falcon chicks experience significant growth and development, laying the foundation for their rapid progression to fledging. Their physical development is complemented by increasing awareness of their environment and social interactions, setting the stage for the skills they will need as fledglings and eventually, as adult hunters. The parents’ role is crucial during this period, providing continuous care and an abundant supply of food to support the chicks’ rapid growth.