Blog # 445 A Day with the Nestlings

June 20, 2023

The 2023 Stewart Park (Youth Bureau) nestlings at @ 3 weeks, courtesy Cindy Sedlacek.

At the end of their third week, the Stewart Park (Youth Bureau) nestlings are healthy and busily eyeing the world around them. They can now regulate their own body temperatures and cool themselves by panting and by laying in the shade of their mother standing with her wings out in the “mombrella” pose.

Nestlings are susceptible to excess heat and cold and must be kept well-covered. They must find shelter during sunny days to prevent dehydration and UV exposure. In bad weather including cold snaps and rainstorms, they must stay warm. Wet chicks can perish when stressed. A major stress arrived without warning from the smoke of the Canadian wildfires, especially on hot days when they pant for hours. It is probable that weak nestlings in the smoke-affected area will succumb to the poor air quality

‘Mombrella’ pose of the mother shades her three chicks, courtesy of Cindy Sedlacek.

Note the dark down on the nestling’s chest and its bulging crop, a storage for fish, by Cindy Sedlacek.

The Osprey nestling in the two photographs above and below is about 20 days old and in the transitional ‘reptilian phase.” The chick has molted the paler coat of feather down

it hatched with and is replacing it with the darker down shown on the bird’s breast. The first full feathers to emerge are the rusty-gold pin feathers on the head and neck.

Adult feathers will emerge from the blood quills, courtesy of Cindy Sedlacek.

One seeks shade under the wing as all three nestlings pant, courtesy of Cindy Sedlacek.

Gradually feathers emerge on the body, flight feathers, and the tail. The flight and tail feathers—the bird’s largest feathers and slowest to grow—eventually emerge from blood quills (shown above), which will quickly disintegrate into flakes and fall away.

During the first twenty days, the male Ospreys double and then triple their fish deliveries during this critical growth period. The nestlings’ appetites double after fifteen days, and the fathers have to keep up with this growing demand for fish. During times of peak demand, when the young are 20 to 35 days old, the father must spend about 20–30% of the day foraging to satisfy his family’s needs. During the period of most rapid growth rate between days 15 to 30 days the nestlings gain about 0.9 pounds a day. By 30 days of age, nestlings are 70–80% of their final size, and energy is rerouted to growing

feathers. As Alan Poole points out in his book Ospreys:The Revival of a Global Raptor, “in the first two-thirds of the growth period bone has priority over feathers, only to have the reverse in the last third.”

At this age, the mother (and father) still dole out the fish in bite-sized pieces to the gaping mouths, but the nestlings are more aggressive and will lunge for the food in their parents’ mouths. Soon they will tear pieces of fish for themselves, although the mother will maintain order in the nest.

Portraits of Hungry Nestlings by Cynthia Sedlacek

Young Ospreys are under tremendous selection pressure to grow quickly and take to the sky to escape predation and prepare for migration. In two months, the young Ospreys will be as big as their parents and getting ready to leave the nest. Check on the nests to watch the youngsters grow and mature.

The territorial Inlet nest male chasing a great blue heron again, courtesy of Cindy Sedlacek.

Eyes to the sky!

Candace

Candace E. Cornell

Friends of Salt Point, Lansing, NY

Cayuga Lake Osprey Network cec222@gmail.com

Guest Photographer: Cynthia Sedlacek

Director of Data Administration and Reporting at Cornell University, Cynthia Sedlacek’s affection and admiration for raptors are evident in her exciting photographs of Ospreys nesting around Cayuga Lake. Her photographs of local Ospreys are incomparable as she captures their essence, their jizz, and their inner bird. From the hard-to-see nestlings to the fast-flying adults, Cindy goes beyond the pale to catch all aspects of Osprey life in the Cayuga Basin. “My camera allows me to capture their beauty in many ways that the human eye can’t see,” she says, “like their spectacular wing positions and detailed feather patterns.” Cindy and her husband Karel are also avid nest monitors for the Cayuga Lake Osprey Network and video stream footage of the campus hawks.