Whooping Crane Migration Update: March 6, 1997

Claudia Fonkert, Macalester College

Can you find Aransas National Wildlife Refuge on a map, near Austwell, Texas? Also try to find Wood Buffalo National Park. (The Park is located on the border of Alberta and the Northwest Territories.) Here's Tom's first report from the Texas Gulf Coast:

To: Journey North
From: Tom Stehn, Aransas NWR
Date: March 5, 1997

Dear Students,

Here at Aransas National Wildlife refuge, the sun is shining, the trees are starting to leaf-out, the temperatures are in the 70's, and the whooping cranes are about ready to start their spring migration. Hormonal changes in the cranes are allowing them to gain weight and build up fat reserves that they will need for the 2,500 mile migration to Wood Buffalo National Park in the Northwest Territories of Canada.

A record 159 whooping cranes made it to Aransas this winter, beating last year's record by one. However, it has been a slightly disappointing year. In November, when I counted 16 pairs with chicks that had been produced in Canada and survived the fall migration, I expected a substantial increase in the population since some cranes always arrive in early December. This year, the additional birds I had hoped for did not arrive. In addition, one of the chicks died of unknown causes shortly after making it to Aransas. Fourteen of the whooping cranes that left here last spring failed to arrive in the fall. This is a higher than normal loss and kept the population from increasing substantially. The biggest hazards whoopers face are collision with power lines while in migration, but disease old age, and illegal shooting can all take their toll.

Both members of one pair that has wintered on the same territory for over 20 years failed to show up. I am always frustrated by not knowing what has happened to these birds, especially when both members of a pair apparently die. One adult female showed up with a chick but no mate, indicating the chick's father had died. (She re-paired with a new, presumably younger male within one week, and the chick has done well.)

USFWS

It is thought that divorces occur among whooping cranes sometimes when a pair are unsuccessful at producing young that survive. It is a survival instinct. This couple was together for 5 years and never produced a chick that lived more than about 3 months.

It has been a good winter for the cranes. Blue crabs are the whoopers' favorite food item. Despite a drought in South Texas enough blue crabs were present in the crane marshes to feed the birds throughout the winter. Although the crabs' numbers have declined the last few months, I hope the whoopers have built up enough energy reserves to have a successful nesting season. In 1994, when blue crabs had been scarce, about half of the whoopers failed to nest that summer! (See impact on 1994 population size, chart below.) We think this was because they weren't in good enough condition.

I'll continue to do an aerial census every week in order to document when the whooping cranes start to migrate. On March 4 we found all 158 whoopers still here. The first whoopers normally start to migrate the last week in March, with most of them leaving in the first half of April. So, I get to enjoy their presence here for another month.

The town of Port Aransas just held a "Whooping Crane Festival" last weekend and 2,500 people attended and were thrilled by the sight of this magnificent, five-foot-tall bird, the tallest bird in North America.

Cheers,

Tom Stehn
Refuge Biologist
Aransas National Wildlife Refuge

The whooping crane is an endangered species with a success story to tell. Their population hit an all time low in 1940 when there were only 22 cranes left in the wild. Their numbers have been steadily building, year-by-year, as shown on the chart below.

Try This!
Using data from the population chart, make a graph to show the growth of the whooping crane population. Then see if you can answer this question:

Challenge Question #1
"During which decade did the population grow at the fastest rate? Why do you think this occurred?"

To respond to this question, please follow the instructions at the end of this report.

How to Respond to Journey North Whooping Crane Challenge Question # 1

1. Address an e-mail message to: jn-challenge-crane@learner.org
2. In the Subject Line of your message write: Challenge Question # 1
3. In the body of the message, give your answer to this question:

Challenge Question #1
"During which decade did the population grow at the fastest rate? Why do you think this occurred?"

Don't Forget!
Please include the name of your school and your location so we can credit you properly for your answers.

The Next Whooping Crane Migration Update Will be Posted on March 20, 1997.