Blog 270 Hatch Day: Size and Birth Order Matters

 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.  

Orpheus guards his mate, Ophelia, and their eggs. Screen shot from the Salt Point Osprey Nest Cam. 

Ophelia’s eggs were laid serially on April 13, 16, and 19 and 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 result in a size and maturation hierarchy in the hatchlings. 

The much anticipated Salt Point Osprey Hatch Day has arrived! Ophelia’s first egg of  2020 hatched, after 38 days of incubation, on May 20, 2020. The egg started hatching sometime around at about 7 am as shown by footage on the Salt Point Osprey Nest  Cam. A half egg shell is visible in the footage as well as the small hatchling. Welcome wee Osprey! 

Orpheus’ and Ophelia’s first hatchling of the season. Screen shot from the Salt Point Osprey Nest Cam. 

Hatching can be a draining 3-day process for the embryo. By repeatedly tapping on the cell wall, the embryo uses its temporary egg tooth on top of its beak to create the first  “star” break in the cell wall. Continually pecking and using its legs and arms, the embryo pushes on the cracking egg shell until sections begin to fall away. This is an exhausting process leaving the newly born hatchling weak and tired. 

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 into independent birds. In comparison, precocial ducks are born capable of being independent directly after hatching.

Ophelia’s first hatchling is circled in red. Screenshot from the Salt Point Osprey Nest Cam. 

The hatchling is brooded constantly by Ophelia, which is one way a casual observer can tell that the first egg has hatched. For the next 3-4 weeks, Ophelia will not fly away from the nest to eat. Once Orpheus brings a fish and the hatchling is ready, Ophelia will tenderly feed small bits of fish to her young offspring. The hatchling can beg to signal it 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.

Hatchling breaking out of its shell, courtesy of Alan Poole. 

Ophelia’s second egg is expected to hatch on the May 23, and the third egg will hatch a  few days after the second on May 26. The young from the first two eggs will have a  clear a size and developmental advantage over the hatchling from the third. 

Note the size difference between the two siblings. Courtesy of USGS.org.

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.  When satiated, it moves aside to allow the second hatchling to feed. The third hatchling eats last provided there is enough to eat. However, if food supplies suddenly decrease,  the first two hatchlings kill the third. Why don’t the parents stop this fratricidal brood reduction? 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 the survival of the oldest nestling. Average survival rates from numerous colonies on the east coast and include food availability, predation, parasite load, collisions, and disease rates are >95%, 88%, and 38% for the first, second, and third nestlings, respectively. Ophelia and Orpheus raised three healthy fledglings for six years on a row, although one fledge in the second brood was lost to a collision with a  nonfunctional telephone wire at Salt Point. 

Eyes to the sky! 

Candace 

Candace E. Cornell 

Friends of Salt Point 

Lansing, NY 

cec222@gmail.com 

Read!  

On Osprey Time (blog) 

Ospreys of Salt Point 

Explore! 

Cayuga Lake Osprey Trail 

  

Watch!  

Salt Point Osprey Nest Cam

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