Tom Stehn Reports from Aransas: February 2003
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Tom Stehn and Survey Plane |
Who out there ever wants to write a report? Well, this is one I am truly excited about writing because I have good news to share.
The most important thing I do every winter is try to count the whooping cranes. This is my 21st year doing this. The winter is the only time of year when it is feasible to get a total count of the flock. Even then, the cranes are spread out over 35 miles of the Texas coast, and it takes me nearly 8 hours in a small airplane flying transacts back and forth across narrow widths of salt marsh in order to find them all. We would actually fly about 800 miles every week if we ever flew in straight line. I'm not actually doing the flying--I'm simply the observer. I plot all the whooping cranes I find on aerial photographs. This helps me avoid counting the same bird twice.
Here is what I have found out this winter. After two down years in a row, the whooping crane population has rebounded. This winter, there are 185 whooping cranes on the Texas coast. The flock consists of 169 white-plumaged adults, and 16 rusty brown first- year birds that hatched in June, 2002. This 185 total is only 3 less than the all-time peak of 188 back in the fall of 1999.
Recent population totals:
adults young total
1997-98 winter 152 + 30 = 182
1998-99 winter 165 + 18 = 183
1999-00 winter 171 + 17 = 188
2000-01 winter 171 + 9 = 180
2001-02 winter 161 + 15 = 176
2002-03 winter 169 + 16 = 185
The whooping crane population seems to take a downswing every 10 years, and then it grows for the rest of the decade. I'm confident the population has just come through such a downturn. Note the population numbers dropping from 188 down to 180 and then 176. We don't know what causes this cycle, but it may be tied to predator cycles in the far north where the birds nest. Many animals in northern Canada have a 10-year cycle, including snowshoe hares, lynx, rodents, etc. I expect the whooping crane population to grow over the next 6-8 years and get up over 200. The all-time high was 188 back in 1999. The all-time low in the Aransas flock was only 15 birds back in the winter of 1941-42. Thus, this comeback made by the whooping crane is the reason why the species is the symbol of conservation in North America.
This past summer, 16 chicks from 50 nesting pairs survived their first summer and fall migration and arrived in Texas. These youngsters will stay with their parents throughout their first year of life. Their parents teach them survival skills, what to eat and where to find it, how to migrate and where to spend the winter, how to act around other whooping cranes, and how to avoid predators. This is what the youngster learns in his first year of "crane school" being tutored by his parents. It is funny watching the whooping crane youngsters learn how to catch and eat blue crabs, their primary food. They first have to learn by experience that a large blue crab can inflict a painful bite with its claws, so that crabs have to be handled carefully. A crane will use its sharp beak to stab a crab to kill it; then will pull its claws off and swallow the claws whole. If the crab is small, the whole thing gets swallowed whole. If the crab is large, the crane will carry the crab to the dry bank of a pond and peck it apart. One crane can eat up to 80 small blue crabs in one day. When crabs are plentiful, as much as 90% of their diet consists of blue crabs.
The school you are in may not be teaching you how to eat crabs, but is trying to help you prepare for life and to appreciate subjects such as history, art, and music, and teach you communication skills of reading and writing. Soon you will be finished with school, just the same way a young whooping crane "graduates" after one year and is then on his own. We have had one whooping crane youngster this winter finish school early. It separated from its parents early and is now spending time either by itself or with other whooping cranes. I have never observed this break up in the middle of winter before and have no explanation for why it happened. The youngster appears to be doing fine.
In about one month, starting at the end of March, the flock will gradually in small groups start the migration to Canada. But I still have one more month of monitoring the population and measuring food resources available for them. I do this in order to make a judgement about what kind of condition they will be in when they make it back north to nest. So far this winter, food resources have been plentiful. I anticipate a very good nesting season this summer and counting a record high number of whooping cranes when they return in the fall.
Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
P.O. Box 100
Austwell, TX 77950
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