Journey North Whooping Crane Spring 2005

Tom Stehn

Photo Heather Ray

April 14, 2005

Dear Journey North,

It’s happened, and right on schedule. As usual, the majority of the flock began migration the second week in April. An estimated 127 whooping cranes (consisting of 103 adults and 20 young) or 59% of the flock started the migration between April 6 and April 13. Since late March, 89% of the flock (181 total cranes) has initiated migration. Present on the April 13 census flight were 18 adults, 9 subadults, and 7 chicks.
All of the remaining cranes except possibly a few subadults are expected to begin migration in the next week. Adult cranes always depart the wintering grounds by April 20th since they have to travel north to Wood Buffalo National Park in Northwest Territories, Canada to nest. (Subadult cranes, ages 1 to 3 or 4 years, are too young to breed; they do not feel the same urgency to hurry back to Canada.) Our next census flight is scheduled for April 27. This allows us time to see if they have all departed by then.

Getting Ready
The best day in the past week for migration was April 9, a day when presumably a lot of the cranes departed. This was on a Saturday. I think the cranes were busy all week working, doing their daily chores of catching crabs and patrolling their territories to keep all other cranes out and thus protecting their food supply. With the work week over, many cranes on April 9 left for a long weekend. But it’s far more than a weekend trip, since it will be 6 or 7 months before they return to Aransas. They will migrate 2,400 miles, a trip that takes 3 to 4 weeks. They will travel anywhere from 200 to 400 miles per day. When conditions are favorable (providing thermal currents and tail winds), the cranes will fly about 7 hours per day. If the winds are in their faces, they will stay put. They will look for food to eat near wherever they have found a small pond or wetland to roost in for the night where they are safe from predators. They have to do about what I do when I travel: cover a lot of miles, and then look for someplace to sleep and something to eat.

Why Do They Leave at Different Times?
The crane migration has been taking place for the past 3 weeks and departures will continue for another 2 weeks. Thus, many of the cranes are leaving at different times. This is an advantage to the flock in case of hazards the cranes encounter on the migration.Sometimes cranes can encounter severe blizzards and actually be killed by freezing sleet. Or they could stop in a wetland where they might be exposed to a disease outbreak. But the largest source of crane mortality is collision with power lines that the birds don’t see when flying, especially late in the day or early in the morning when making short flights from their stopover locations. With cranes leaving at different times and stopping at different places, not all the cranes are exposed to the same hazards. That ensures that some cranes will survive and thus it’s an advantage for the flock to migrate in small groups at different times.

Fueling Up on Crabs and Snakes
On today’s census flight, most cranes were in ponds that were drying up with the cranes feeding on small blue crabs. One adult crane was observed holding a large snake and its chick sprinted over to get the snake. Now that’s a meal that will provide energy for the long migration.

Tom Stehn
Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas National Wildlife Refuge

April 13 Flight report:
An aerial census on 13 April, 2005 of the Aransas National Wildlife Refuge and surrounding areas estimated the number of whooping cranes present at Aransas at 27 adults + 7 young = 34 total. The current estimated size of the Aransas-Wood Buffalo population is 182 + 33 = 215.

Recap of cranes observed on the flight: (34)
Refuge 11 adults + 3 young
Lamar -
San Jose 5 adults + 2 young
Matagorda 7 adults + 2 young
Welder Flats 4 adults + 0 young
Total 27 adults + 7 young = 34 cranes

Remarks: Excellent viewing conditions and light winds were present throughout the day with a complete census flown. Flight conditions can’t get any better.
An estimated 127 whooping cranes (103 adults and 20 young) have started the migration since the last flight on April 6. The best day in the past week for migration was April 9. The presence of the West Shell Reef family group that had been overlooked last week indicated that 157 cranes had actually been present on the last flight April 6. Present on today’s flight were 18 adults, 9 subadults, and 7 chicks. The family group of cranes visible from the refuge observation tower has migrated. The next census flight is scheduled for April 27.

On today’s flight, tides were at mid-range (2.5 mlt), higher than last week. Most cranes were in ponds that were drying up with the cranes feeding on small crabs. A few cranes were in dry vegetated marsh. One adult crane was observed holding a large snake and its chick sprinted over to get the snake. No cranes were in open bay habitat or on prescribed burns.