Blog 437 Hatch Day: Size Matters

Newly hatched, eldest on ‘right, youngest coming out of egg shell. Courtesy of Irish News.

Three newborn hatchlings courtesy of Pinterest. Note the white egg tooth a top each beak. 

All animals start life as an egg, but only birds have evolved to enclose their egg in a hard shell filled with massive amounts of nutrients for the developing embryo. Each egg is a self-contained package that must be cradled and kept at about 98°F to allow embryonic growth to occur. The egg requires continual parental care until a second birthing or hatching occurs.

Ursula’s eggs were laid serially were of diminishing size and volume. Typically, the first egg in a clutch has more mass than the second egg and is visibly larger than the third. Both the asynchronous laying and sequentially decreasing size and volume results in a brood with a size and maturation hierarchy with the first egg yielding the largest hatchling. Without the Nest Camera functioning, I can only guess that two eggs have hatched and the third will follow suit any day. The Nest Cam Screenshots are from 2022

First egg hatching at Salt Point, courtesy of Salt Point Nest Cam.

Four-day- and one-day-old hatchlings wait for their sibling to hatch, courtesy of Cornell Nest Cams.

Born down-covered and weighing less than 1.8 ounces, the semi-precocial hatchling is capable of weak movements at first and is soon able hold its head to beg for food, but only briefly. Semi-precocial chicks must be tended until they grow quickly into independent nestlings. The day-old hatchling is capable of waddling over to the nest rim and defecating over the side of the nest.

As described in Blog #436, the 3-day hatching process is exhausting for the embryo. Repeated tapping on the cell wall and pushing the shell with their legs and arms is exhausting leaving the newly born hatchling weak and tired. In comparison, precocial birds like ducks and geese are born capable of being independent and swimming away directly after hatching.

The young hatchling is tenderly brooded by Ursula. The casual observer can tell that the first egg has hatched when Ursula stops taking her food to eat in a tree. For the next 3-4 weeks, Ursula will eat in the nest and only leaves the nest to bath and stretch her wings while Orpheus cares for the young ones. When Orpheus brings a fish, Ursula will caringly feed small bits of fish to her small offspring. The hatchling can beg to signal its hunger, but it must stay next to its mother for warmth as it is unable to regulate its body temperature. Like it’s parents, the hatchling pants to cool off and gets all its water from the fish it eats.

Hatchling breaking out of its shell, courtesy of Cornell Nest Cams.

Ursula’s third egg is expected to hatch any day. It’s easy to see that the young from the first two eggs will have a clear a size and developmental advantage over the third hatchling.

At mealtimes, the hatchlings establish size hierarchies, with the largest hatchling (with the highest probability of surviving to fledging), pushing its way to its mother to feed first.

Note the size difference between the siblings, courtesy of PBS.

When satiated, it moves aside to allow the second hatchling to feed. The third hatchling usually eats next followed by the mother who often gets the dregs—bones and fins. However, if food supplies suddenly decrease, the first two hatchlings kill the third. Do the parents try to stop this fratricidal brood reduction? No. Brood reduction adjusts the brood size to levels at which fishing can be sustained and minimum growth rates can be maintained. This form of brood reduction is common in birds of prey and necessary for the sake of a healthy generation. The staggered birth order insures the survival of the oldest nestling. However, the Osprey feeding in Cayuga Lake have a wealth of food for the taking and do not practice brood reduction.

Average survival rates from numerous colonies on the east coast, including fatalities from lack of food, predation, parasite load, collisions, and disease rates are >95% survival rate for the eldest hatchling, 88% survival for the second hatchling, and 38% for the smallest hatchling. Orpheus has a great track record, having raised three healthy fledglings each year for eight years in a row, an excellent reproductive effort for the Salt Point nest.

Eyes to the sky!

Candace

Candace E. Cornell

Cayuga Lake Osprey Network

Friends of Salt Point

Lansing, NY

cec222@gmail.com

Read!

 On Osprey Time: Ospreys of the Finger Lakes

Explore!
Cayuga Lake Osprey Trail

Cayuga Lake Osprey Driving Trail

Watch!

Salt Point Osprey Nest Cam

Protect Ospreys!

•Stay 300 feet away from nests during the breeding season. 

If the Osprey vocalizes, you are too close! Back off Immediately.

•Carry binoculars to view wildlife from afar.

•Help keep local waters clean, healthy, and safe.

•Recycle used fishing lines, twine, and nets, which can kill Osprey.

•Join the Cayuga Osprey Network and volunteer to help monitor Osprey nests: cec222@gmail.com.