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Captive Rearing: Egg Production and Incubation

Have you ever wondered where the whooping cranes that follow the ultralights come from?  All birds for the reintroduction come from captive flocks. Because there are only 247 whooping cranes in the single natural wild flock we don’t want to remove any birds from that flock. The three primary captive breeding centers with whooping crane pairs that produce eggs for the reintroduction project are at Patuxent Wildlife Research Center (Maryland), the International Crane Foundation (Wisconsin), and the Calgary Zoo (Canada).  Additional breeding pairs are also present at the San Antonio Zoo and the Audubon Center for Research of Endangered Species at the Audubon Species Survival Center in New Orleans, Louisiana.  Whooping crane eggs used for the ultralight project are incubated and hatched at Patuxent.

Egg Production at Patuxent

In the wild, whooping cranes usually lay two eggs (called a “clutch”) with only a single chick surviving to fledging (definition provided in pop-up).  At Patuxent, after a pair lays their first two eggs, staff members remove the clutch from the nest, which causes the pair to lay another clutch in about 10 days. By removing their eggs, whooping crane pairs at Patuxent are induced to lay six to eight eggs during a breeding season, compared to two eggs laid by wild whooping crane pairs.  Patuxent whoopers are usually allowed to incubate their last egg, and raise the chick themselves.

In any given year, Patuxent holds 7 to 12 breeding pairs of whooping cranes. Generally they lay about 50 eggs during the breeding season, but only 50 percent turn out to be fertile. Usually 20 to 22 chicks hatch from the fertile eggs.

Incubation

“When an egg is first handled, we put it in a betadyne solution, and we use latex gloves so as not to transmit any bacteria from our hands,” said Jonathan Male, supervisory biological technician with USGS. Male has worked at Patuxent for more than 20 years.  If the egg is fertile and healthy, a pair of sandhill cranes is selected to incubate the egg for ten days. Whooper eggs do best if incubated by cranes instead of mechanical incubators, at least in the early stages. “Sandhills are used because they are readily and easily available for us; they are found in North America, and they are large enough to incubate two whooping crane eggs,” Male said. “We have also used chickens as back up incubators in the past.”

Patuxent employs a rating system to determine the best pair of sandhills to incubate an egg. A sandhill pair will incubate and raise sandhill crane eggs for at least two years. “After they show they are good parents, then we will give them a whooping crane egg,” he said. Male said each pair can serve as surrogate parents at Patuxent for around 15 years.

Each egg is given an identification number based on the parent's pen location and the order in which the egg was laid. The surrogate sandhills incubate the whooper eggs for 10 days, with the male and the female alternating care of the egg. After 10 days, the egg is removed from its surrogate parents, weighed and examined for fertility.  

Weighing the egg is crucial, as excessive weight loss indicates dehydration. Although a fertile egg does lose weight as the chick grows inside, too much weight loss can be fatal. Patuxent can often remedy problems like this, so the egg weight is critical.

After the first 10 days, if the egg is fertile and healthy, the flock manager decides which pair of sandhills would be best to incubate the egg for the next ten days.  At 20 days, it is safe to place the egg in a mechanical incubator for the last 10 days of incubation.

Just hours before hatching, movement within the egg can be detected and peeping sounds heard.  For chicks that will be used on the ultralight-led migration, Male says the handlers begin to play sounds of the ultralight aircraft engine to begin the imprinting process.

Egg production and incubation are only two steps in producing and raising whooping cranes for reintroduction.  Visit Patuxent’s website to read more about all that is entailed (links below).  If you are in the area, visit Patuxent Research Refuge.

Health Checks and Anatomy

Breeding Season Preparations

 
The Courtship of a Whooping Crane………in Captivity

Whooping Crane Chicks in Training

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