One day, late in January, a friend and I watched two Steller sea lions swimming near Pt. Louisa. One of them held a front flipper high above the water for several minutes. We often see this behavior, but usually the flipper is not raised for so long. Sea lions do this as a means of thermoregulation, either getting rid of excess internal heat or gaining heat from the air. In this case, it seemed more likely that the lion had become too hot and was trying to lose heat. They carry a heavy blanket of insulating fat, which is useful in cold water, but a burst of high activity might elevate the internal temperature too much. Eventually, both sea lions swam normally and quickly around the point and headed up-channel.
Again at Point Louisa, but on a different day, we saw a cormorant dropping down to land on the water. No way to miss that one…all angular wings and neck and legs. As it rested quietly on the water, we could see that it had a light-colored bill, which let us say it was a double-crested cormorant. The alternative having a light-colored bill is extremely rare here.
Double-crested cormorants nest mostly in the central part of North America, but they also use various spots along the coasts. In winter, they spend much of their time in coastal waters. They eat mostly fish, as do the related anhingas, pursuing the prey underwater. However, they capture fish in different ways. Cormorants grab their prey in their hooked bills, but anhingas spear prey on their pointed bills. Both kinds of birds have to grasp a slippery, wriggly fish between the upper and lower jaws, before swallowing it headfirst. And both have a special adaptation for dealing with fishy prey: I recently learned that, unlike all other birds, cormorants and anhingas have a special little bone (called the occipital style) projecting from the back of the skull. This slim bone anchors the substantial muscles that forcibly close the lower jaw on a captured fish, pinning the prey between the jaws.
An adult double-crested cormorant flies low. (Photo by Bob Armstrong)
A stroll on the Treadwell trail above Sandy Beach in mid-January was notable for the lack of avian activity. But along the bank above the trail we found many colonies of a flat liverwort growing over soil and wood, generally in damp places. On a nice day, these colonies were quite conspicuous.
Liverworts are distantly related to mosses, and there may be about 9,000 species of them. They grow in all sorts of terrestrial habitats except the very dry ones or those exposed to lots of direct solar radiation and also in some fresh waters. Only some of them are flat (the structure is called a thallus); others have tiny leaf-like structures on the upper surface. Like the mosses, liverworts exhibit alternation of generations. The plants we observe are gametophytes, with one set of chromosomes (haploid), and they bear the sex organs. In some cases the sexes are separate, in others both male and females occur on the same gametophyte. When wetted, the male organs may release sperm, which swim over to the female organs to fertilize an egg. The resulting sporophyte has two sets of chromosomes (diploid), but by meiosis it reduces the number of chromosome sets to one. Growing right up on top of the flat “thallus,” the sporophyte will shed its spores to be carried by wind or water to new sites, where they give rise to the alternate generation of gametophytes.
Liverworts have several roles in ecosystems. They may be an emergency food for caribou on the tundra, but on a more regular basis they may be eaten by insects, snails, nematodes (round worms), tardigrades (water bears), and small rodents. That contributes to nutrient cycling in the ecosystem. Liverworts also absorb a lot of water, helping to control erosion, as they were probably doing along the trail. Their colonies also accumulate detritus that can eventually provide a substrate for mosses and vascular plants to become established.
Down on Sandy Beach one day, we watched two ravens bullying another. The victim was flat on its back on the sand, while the two aggressors hammered at it repeatedly, wings aflutter. We didn’t know the outcome, because the interaction was interrupted by a curious dog, but as the birds flew away, the aggression continued. Naturalists have seen this sort of bullying from time to time, but I have not heard a good explanation for it.
At the end of Sandy Beach when the tide was out, there was a broad swathe of sand between the water’s edge and the snow at the upper level. On that sand were hundreds of eagle footprints. The bird(s) had marched along the beach, parallel to the water’s edge, many times. Back and forth, over a distance of ten meters or more. A puzzle!
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
This liverwort is common along the Treadwell trail. (Photo by Mary F. Willson)
