Tom Stehn Reports from Aransas: April 15, 2004

Dear Journey North,

By mid-April, the whooping crane migration has gone from “on schedule” To “ahead of schedule.” I was amazed on my aerial census flight April 14th when we could only find 14 whooping cranes remaining at Aransas, whereas one week ago (April 7th) we counted 109. The weather had been absolutely impossible for migration April 11-13 when a cold front brought strong north winds gusting to 30 mph. Cranes are just not going to struggle north against such strong headwinds. They would much rather stay at Aransas a few more days and fatten up on delicious, nutritious, high-in-fat-and-protein blue crabs, their favorite food. A crane can eat up to 80 blue crabs a day, which is quite a feast for a bird that only weighs 15 pounds. So the 95 cranes that started the migration since my April 7 flight did so April 8-10th, or perhaps late morning on April 14th. I say that because I believe that 5 of the 14 cranes that I counted first thing in the morning on April 14th could not be found later in the day. I had found those five by 9 AM, before the thermal currents built up as the land warms during the day. When I went back to check on them that afternoon, they were nowhere around--and had presumably started migration later that morning. That leaves currently just 9 whooping cranes at Aransas.

Who's Left? Family Stories
Of the 9 cranes remaining, one is a single adult crane with a chick that the adult had raised last summer after presumably losing its mate sometime after the chick was hatched. Since both adults take turns sitting on the egg, it is unlikely the mate died before hatching of the egg. All winter long, I sometimes noticed a second adult crane near the widowed adult. This second adult would sometimes apparently chase the chick off, since I often found the chick several hundred yards away from its parent. I sometimes found the chick right next to both adults. But on April 14th, just prior to migration, the widowed adult was all by itself--initially with the chick underfoot, and later with the chick about 200 yards away. So the winter "dating" by the adult crane didn't lead to a lasting relationship, which in cranes we call "pairing." I believe the widowed adult is a female, since male cranes will normally find a new mate in a hurry. I once documented a male finding a new female within 36 hours after its mate had died. Cranes just about always mate for life, but will re-pair if a mate is killed. I have documented a few instances of “divorce” in whooping cranes, where they will switch mates and one case of reconciliation when a pair split up for a year and later got back together. This “reconciliation” pair successfully brought a chick to Aransas this winter.

Male or Female?
Although male and female whooping crane look alike, the male is usually a little larger and has a lower-pitched voice. Also, when the pair does what we call a unison call (a choreographed song), the male will usually lower its wing tips and show the black primary feathers at the tips of the wings, whereas the female normally keeps her wings folded closer to her body with only the white feathers showing. Since I’m talking about how to tell a male from a female whooping crane apart, this reminds me of the joke: How do you tell a male and a female alligator apart? The answer, I’ve been told, is “very carefully?!”

Predictions and Questions
Ninety-five percent of the whooping crane population has started migration. Strong southeast winds are forecast for the next three days, so most of the cranes should be gone by next week. Whooping cranes are currently being reported all the way from Texas to North Dakota. They should cross into Canada shortly. My job now is to see when the last 9 whooping cranes depart from Aransas. Will they all go, or will one decide to stay behind and spend the summer at Aransas, an event that happens every once and a while? I also wonder if the single adult with her chick will migrate together, or whether the chick that has showed so much independence this winter will migrate later, after its mom has already departed. If the chick ends up migrating by itself, it’s not something to worry about. One-year-old cranes are ready to become independent, and must do so anyway if they accompany their parents northwards to Canada before their parents build a nest. This crane, even by itself, can find its way back to the nesting grounds, which I sometimes feel is a miracle--or at least one great job of navigating.

Tom Stehn, Whooping Crane Coordinator
U.S. Fish and Wildlife Service
Aransas NWR
Austwell, Texas

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