Thursday, December 18, 2008

Species Profiles: The Bald Eagle

The process of listing and de-listing a species in the state of Kansas is both confusing and simple.  If a species is listed by the feds, it is automatically added to the Kansas list (if it is an animal).  On the other hand, if a species is de-listed by the feds, the species must be petitioned to be delisted in Kansas.  For most people I talk to, their reaction to this is that's stupid.  As I've discussed elsewhere, often there are very good reasons to continue to protect a species in one area that may be far from threatened elsewhere.   

However, the most recent round of petitions for listing or delisting species in the state of Kansas is now up for review, and the Bald Eagle (Haliaeetus leucocephalus) has been the subject of delisting petition (along with the Peregrine Falcon and the Broadhead Skink).  In my professional duties for KDWP I am not a part of the
 committee that determines listing or delisting of species, but I have heard that the Bald Eagle is likely to be delisted.  So I figure I better get a species profile of this popular bird up before it is out of my realm of interest.

How much introduction does a bird like this need?  Americans are well aware that the bird serves as a (perhaps the) national icon.  Less may be aware of Benjamin Franklin's scathing criticism of t
he bird (sources here and here):
I wish that the bald eagle had not been chosen as the representative of our country, he is a bird of bad moral character, he does not get his living honestly, you may have seen him perched on some
 dead tree, where, too lazy to fish for himself, he watches the labor of the fishing-hawk [osprey], and when that diligent bird has at length taken a fish, and is bearing it to its nest for the support of his mate and young ones, the bald eagle pursues him and takes it from him.... Besides he is a rank coward; the little kingbird, not bigger than a sparrow attacks him boldly and drives him out of the district. He is therefore by no means a proper emblem for the brave and honest. . . of America.. . . For a truth, the turkey is in comparison a much more respectable bird, and withal a true original
 native of America . . . a bird of courage, and would not hesitate to attack a grenadier of the British guards, who should presume to invade his farmyard with a red coat on.
That bit about the turkey, it doesn't necessarily come from Franklin's support of the turkey as a national bird, but 
rather from the poorly drawn seal from the early continental congress (shown below).  The Eagle was also an important bird for Native American Mythology, although the Golden Eagle (Aquila chrysaetos) was probably much more abundant throughout the continent.  

All eagles fall into the Accipitridae family, although where they fall is a matter of some dispute.  As befits one of the most well-studied species in North America, relatively more is known about the bald eagle than some other eagles.  Bald eagles fall into the Sea Eagle category, and are almost morphologically indistinguishable from their nearest living relative the White-tailed Eagle (or just Sea Eagle).  That species pair diverged from other eagles ~10-20 million years ago. 

This bald eagle killed a whale!  Or found one dead on the beach...Same difference.

I tend to get very bored when talking about birds because I have poor eyesight and don't really see them very well out in the field.  So let's talk about why I and many other people have no problem seeing lots of small birds (e.g., sparrows, swallows, cowbirds, etc.) and hardly ever get to see a bald eagle or heron from close up.  Surprisingly enough, it probably has a lot to do with energy kinetics.  

See, smaller birds, mammals and lizards tend to contract their skeletal muscles faster than larger birds, mammals and lizards.  In the case of birds, this means faster (and more powerful) wingbeats per unit muscle in a sparrow than a bald eagle, so a bald eagle has to pack on a lot more muscle to get the same amount of acceleration.  All that extra muscle means that big flying birds exist right at the limit of being able to fly at all.  So those big birds end up using a lot of 'runway' to get off the ground.  I'm sure everyone has seen a duck or goose running across a pond or lake before taking off.  Those birds are not only big, but they are heavy, and built for long migratory flights across continents.  

As a result of all that, the proximity that triggers a flight response from a bird varies tremendously.  Small, mobile birds can get off the ground and out of danger very quickly, whereas a bald eagle takes a few moments, and a goose takes even longer.  So a sparrow will let you get a lot closer than a bald eagle.  This is also why you occasionally see a few small birds harrassing a large hawk.  The hawk is simply incapable of manuvering its bulk around in the air fast enough to deal with the smaller birds.  

Back to Bald Eagles?  Ok, sure.  The Bald Eagles are top predators, and primarily fish eaters (as the whole Sea Eagles thing implies).  They tend to stick to major river corridors in continental interiors and congregate along coastlines.  Alaska has the largest population of existing Bald Eagles, despite a concerted effort by salmon harvestors to kill them off in the early 1900s.  In general, the eagle was the subject of human harassment and competition, and dramatically declined from pre-Columbian levels as the United States became more populus through the 1800s and into the early 1900s.  Protection for the Bald Eagle was first enacted long before Federal Threatened and Endangered Species laws, by the Migratory Bird Treaty and the Bald Eagle Act.  

Those laws might have worked to restore Bald Eagles if not for the Greatest Generation's plan to kill everything on the planet.  What am I talking about?  DDT.  DDT is arguably a huge boom to mankind, since it basically eliminated malaria from large portions of the globe, but it also caused dramatic and unanticipated impacts on human and environmental health.  The overuse of DDT and similar pesticides essentially created the modern environmental movement (see Carson, Rachel), and lead to the passing of the federal Endangered Species Act.  

Unfortunately, since its passage, the ESA has been more-or-less continually gutted in favor of economic conerns, and only a few species have ever been successfully removed from the Endangered Species list.  (I could go on and on about why the ESA isn't a great idea, but the reality is that it isn't a terrible idea either).  On June 28th, 2007 the Department of the Interior announced the Bald Eagle was going to be delisted, which came as little surprise.  The Eagle's numbers have been rising dramatically in recent years.  I've personally seen over 20 in the last year despite living in Kansas, where they are very scarce.  

I even saw one today.

1 comment:

Anonymous said...

you said it was as bald eagle ....
but couldn't even see his balls