Whooping Crane Migration Update: March 6, 1997
Claudia Fonkert, Macalester CollegeEach spring the entire flock of wild whooping cranes takes the annual 2,500 mile journey from their wintering grounds in Texas to their nesting grounds in northern Canada. They usually arrive in late April or early May just as the ice and snow is melting from the marshes. Tom Stehn, Refuge Biologist at Aransas National Wildlife Refuge in Austwell, Texas keeps a careful watch on the cranes all winter. He will provide updates this spring as the cranes prepare for their migration. His first report is attached below.
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
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.)
USFWSLast winter, a pair that had nested together for 5 years split up and the male crane resided on his territory with a younger bird. His former mate hung around, but kept getting chased off by the new female. The newspapers picked up the story and called it the "whooping crane divorce". Well, this saga may turn out to be a "trial separation" rather than a divorce. The original pair was apart for about a year and even migrated separately in the fall of 1996. Imagine my surprise when I found them together again on their former territory here in November! They sure look like a firmly bonded pair again. We'll see if they nest together in 1997.
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.
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.
Challenge Question #1
To respond to this question, please follow the instructions at the end of this report.
Whooping Crane Population Size
How to Respond to Journey North Whooping Crane Challenge Question # 1
Challenge Question #1
"During which decade did the population grow at the fastest rate? Why do you think this occurred?"
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.