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Whooping Crane Migration Update: April 9, 1998
Today's Update Includes:
- Field Notes High Above Aransas
- Field Notes And Today's Migration Data From The Great Plains
- Discussion of Challenge Question # 6
Field Notes High Above Aransas
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Tom Stehn |
From: Tom Stehn
Aransas National Wildlife Refuge
Austwell, Texas
And They're Off!
The whooping crane migration is in full swing. On April 2nd, I found only 139 cranes
on my aerial census flight. This means an estimated 42 whoopers have started the
spring migration!
About 23 cranes (five families and four pairs) started the migration sometime between
March 26 and April 2. And then on April 5, Whooping Crane Tour Boat Captain Ted Appell
watched 14 cranes start the migration from the south half of the Aransas refuge.
Departures occurred between 9:50 and 10:30 AM, and included families, pairs, and
subadults. The Mustang Lake/Nyarling family that refuge visitors see from the refuge
observation tower also departed that day.
Cranes Head Home On South Winds
Even with so many cranes leaving within a short time period, these cranes have staggered
starting times and leave in small groups of 2 or 3. Sometimes, two such units will
join forces so possibly 5 cranes, or occasionally a few more, may be flying together.
The departure of a territorial pair often "influences" its neighbors to
leave shortly afterwards. All kinds of vocalizations are going on as the cranes depart.
I wish I knew what they were saying. We might think they are saying the equivalent
of "See you later. I'm off to Canada to nest", but in reality, the loud
whoops are presumably more related to their territorial and dominance behaviors.
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I'm anxious to do my next census flight on April 09 to see how many birds departed in early April. Probably I'll fly over parts of the whooping crane range and find most of the birds still present on their territories. Other sections of marsh will have only a few cranes left and feel very empty. This will demonstrate just how individualistic the whoopers are.
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Migration Route |
Soon the telephone should be ringing with sighting reports of the whoopers as they make their 2,500-mile journey to the Northwest Territories of Canada.
Until next time,
Tom Stehn
Whooping Crane Biologist
Aransas National Wildlife Refuge
Austwell, Texas
Field Notes From The Great Plains
On the Lookout!For years, Mr. Wally Jobman of the USFWS Ecological Services Unit has organized a network of observers across the Great Plains who report whooping crane migration sightings to him. Again this spring, he will forward these to you. At the same time, he'll provide a brief weather summary, describing the past week's weather patterns as they relate to whooping crane migration. Here is his first field report, sent from his home town of Grand Island, Nebraska along the famous Platte River:
To: Journey North
From: Wally Jobman
Greetings from the Cornhusker State! Typical spring weather last week, warm one day and cold the next. Up to 10 inches of snow in north-central Nebraska on Tuesday (3/31). The entire whooping crane flyway in the USA appeared to be pretty wet.
More recently, many sandhill cranes migrated from the Platte Valley, Nebraska, on April 4 and 6. Rain began during the evening of April 6, and continued through April 8 in Kansas, Nebraska, and South Dakota. Sunshine may return on Friday, April 10 and allow the migration to resume.
Thus far during the spring migration eight sightings have been confirmed as follows:
Wally Jobman
USFWS Ecological Services
Grand Island, Nebraska
Discussion of Challenge Question # 6
Last week, Tom Stehn reported on the continuing problem of crane deaths from power line collisions, and we challenged you to think of design changes to help make the power lines less harmful to wildlife. Making these design changes, however, can cause debate because they cost money and might cause power costs to increase.
As you read Tom's comments below, take a look at the "Cycling Through Controversy" Lesson, which is available in the Teacher's Manual at pp. 65 or click below.
But first, many thanks to Tim from Montana, who shared his suggestion based on
the cranes he has seen flying in his family's rice fields. Tim said that "I
have observed cranes landing in rice fields when fog was so thick the cranes could
hardly see me but once they did see me they were quick to leave. I have also heard
cranes flying at overhead at night. It has occured to me the cranes need sound as
well as sight when flying in adverse weather conditions. Powerlines need to emit
some type of chimes or clanging noise to alert the birds of the impending object
in their flight path. Fog horns alert humans to dangers I'm sure there is some sort
of noise the cranes would alert to. My name is Tim I work at Polson Middle School,
Polson,Mt."
pmslib@cyberport.net (polson middle school library)
Thanks also to Tom Stehn, who tells us what steps and devices have been used so far
to these prevent power line collisions. "The USFWS and Power/Utility companies
have done a lot of research to address this issue of bird strikes and power lines.
It is not just cranes - other birds can strike power lines and/or guy wires on tall
radio communication towers, etc.
"The first step is not to allow new lines to be constructed near wetland areas
where bird numbers are concentrated. Sometimes, based on environmental considerations,
lines are re-routed to avoid areas of concern. Or perhaps a line can be placed underground
to avoid the problem. I know at the Bosque del Apache National Wildlife Refuge, the
two ultralight cranes had to make two flights a day over a low power line. The refuge
has requested, and the power company agreed, to bury the line as soon as all the
cranes leave in spring migration so that no hazard will exist next winter.
"If a line exists and can't be buried (after all, putting lines underground
is much more costly than above ground), researchers have found that markers can be
placed on the lines to make them more visibile to birds. You see this around airports
where red balls are placed on the lines to allow pilots to see the lines. This same
technique works well for birds and reduces collisions by 50%. Materials have also
been wrapped around the line in a candy cane striped pattern, and metal rectangular
plates have been hung from lines too, but the balls seem to work the best.
"Young first-year cranes seem more vulnerable to striking power lines compared
to their parents. Perhaps that is because they are not as skilled a flyer when making
a last-ditch effort to avoid a line they have seen too late, or perhaps they are
not as skilled at recognizing lines, and probably just aren't paying as much attention
to things around them.
"However, even if bird strikes are reduced by 50%, the continued construction
of more utility lines in this country makes the bird strike problem grow every year.
And that will continue as the human population continues to increase.
"Are you willing to pay a few cents more every month on your utility bill to
ensure lines are marked properly? I would love every power line in the whooping crane
corridor to be placed underground, but unfortunately this would be too costly and
not practical since the migration corridor is about 150 miles wide by 2,500 miles
long. Thus, power lines continue to be the number one source of mortality for whooping
cranes."
"This is a good example of a human-caused factor that helps make and keep a
bird endangered. After all, man-caused changes in the landscape that affect wildlife
habitats are what cause species to become endangered. In very few cases are species
these days going extinct becase of natural selection that is not influenced by man.
We as people are the culprits, and thus we have a responsibility to save species
that are endangered."
The Next Whooping Crane Migration Update Will be Posted on April
16, 1998.
Copyright 1998 Journey North. All Rights Reserved.