Saturday, August 2, 2008

Two Things Middle Yukon

Bank Swallow colony, east of the camp on the Yukon. Bank Swallows always nest in colonies; this is a rather large one.

Bank Swallows make good bear food, when the bears can get it--note the claw-marks. Click on the images to enlarge the view. In spite of this apparent mis-match, swallows in Alaska are not sorely pressed -- in Alaska.

As with many migratory species, the Bank Swallow is listed as an endangered specie in California where it is under threat from human activities.

The colony serves as a mutual-aid society. Swallows forage from dawn 'til dusk and strive to maintain close contact with the nest and young during that time. Swallows communicate good sources of food to one another, increasing efficiency and decreasing exposure among members of the colony.

Close-up of the Aspen Leaf Miner worm. Nearly all of Alaska's quaking aspen population is affected by the Leaf miner moth. Very tiny, the larvae live off the leaves and in less than a decade have spread throughout the state. The tracks of the miner worm give whole hillsides of trees a pale, gray-green cast. Trees can survive the moth, though it does retard their growth rate. Field biologists have found that trees that -- through genetic chance -- secrete nectar near their leaves are able to fend off the worm. The nectar attracts ants; the ants eat the miner larvae.

Dendrologists and entomologists are watching this remarkable explosion in the miner population carefully. Will the leaf miner ultimately destroy the aspen population? Will ants alter their feeding patterns to seek out the miner worm rather than the proxy nectar? Will aspens adapt as a population to produce nectar more commonly, thus attracting the ants and fighting the miner worm?

Trees have remarkable adaptive capacity that we only slightly understand. During the gypsy moth infestation of southern New England early in the 1980's, oak trees fought back against the tent caterpillar -- a gestational stage of the gypsy moth -- by altering the chemistry of their leaves. While this is remarkable in itself, even more amazing was their ability to warn other trees.

I can recall those summers from my childhood. Standing in the woods on a quiet early summer day, millions of masticating caterpillars created a persistent susseration that sounded like light rain. What I couldn't hear were Oak trees under attack sending out a distress call in the form of jasmonic acid. The acid drifted out on the air from tree to tree, prompting unaffected Oaks to increase the toxicity of their own leaf chemistry in advance of the assault.n

Might not the Quaking Aspen develop a similar response? May it already? With nearly every acre of the Alaskan population affected, it is to be hoped.

n: See Reading the Forested Landscape by Tom Wessels.

1 comment:

Mens Suits said...

Amazing colony its look like in discovery channel.