Tom Stehn Reports: Hoping for Eggs
May 2, 2008
<< Back to Update

As you read Tom's report this week . . .
  1. How many Whooping Cranes are currently in captivity?
  2. When do Whooping Cranes lay eggs, and what prompts them to lay?
  3. How many eggs can a female in captivity be expected to lay per year?
  4. How do cranes incubate their eggs?
  5. What is the concern about egg production this spring?

Dear Journey North,

Every April the flock managers of the five facilities in North America that breed Whooping Cranes get together on weekly phone calls to share information about egg production. These folks and their staffs (maybe 40 people overall) are responsible for caring for the 148 Whooping Cranes currently in captivity.

Timing is Everything
Whooping Cranes start laying eggs as early as April in southern captive locations, such as New Orleans, Louisiana and San Antonio, Texas. In the north, egg laying generally takes place later. It extends into June, equivalent to the timing of the wild Whooping Cranes in Canada. Cranes respond to (1) temperature and (2) day length (photoperiod) to adjust their time of breeding to the climate.

A Disappointing Year for Egg Production

How are these precious eggs kept safe when they are shipped? Read more here.

Photo Mark Nipper, WCEP

This year, the egg laying has been a disappointment. The egg laying has been slow. Some eggs were infertile. Other eggs have been broken by the parents. The captive cranes at Calgary did not follow "the rules" and laid a few eggs quite early. At one point, all the eggs had to be taken from the Calgary cranes because of a snowstorm and very cold temperatures. These conditions would have threatened the eggs if one of the adults stopped sitting on the eggs for even a short time. All the eggs were placed in an incubator where the storm could not affect them.

Taking the eggs from the Whooping Cranes when they are laid results in the female crane then laying a second or even a third clutch of eggs. Since most clutches consist of two eggs, one female in captivity can be coaxed to lay about 6 eggs every year. Both the male and female Whooping Cranes take turns sitting on the eggs. This teamwork allows one adult always to be out getting food to eat.  Taking turns makes it less stressful for the adults to sit on the eggs for 29-30 days until they hatch.
On April 30: Count of Possibly Fertile Eggs
Patuxent Wildlife Research Center 11
San Antonio Zoo 0
Calgary Zoo 4
New Orleans 2
International Crane Foundation (fertility unknown at this date) 3

An Enormous Challenge
It is very, very hard to successfully get Whooping Cranes to breed. Of the 15 species of cranes in the world, I think Whooping Cranes are the hardest to breed. I am very worried that we will not have enough hatched chicks this year to meet our target of releasing about 30 whooping cranes into the wild population that migrates between Wisconsin and Florida.  The flock managers are doing everything they can to have a successful production year. But ultimately it's up to the captive cranes to decide if they are going to have a good year or a bad year producing eggs. So far, I'm afraid it looks like it might be a mediocre-to-bad production year. Keep your fingers crossed for better luck in the weeks ahead. I guarantee that we've got 40 people doing everything they possibly can to help the cranes produce young this year.

Tom Stehn

Tom Stehn
Aransas National Wildlife Refuge