We happened to be in the Salt Lake City area in early October to visit family so I made an excursion to two of my favorite aquatic natural areas, Farmington Bay Waterfowl Management Area and Antelope Island. The Great Salt Lake is much saltier than the ocean and birds primarily feed on either brine flies or brine/fairy shrimp. Such a tiny diet seems strange but the enormous abundance of these small prey allows for the presence of large numbers of migrants. The flow of fresh water into the lake has been reduced lately and the size of the salt lake is much reduced with large mud flats on either side of the causeway to Antelope Island. One interesting bird we found feeding on the mud flats was the long-billed curlew which was probing the crevices in the drying mud for food. The bill of this bird is just simply bizarre in relation to its body size; it could be viewed as a smaller version of the ibis body plan.
In September there would usually be large numbers of migrant phalaropes, both Wilson’s and red-necked present along the causeway. These had mostly departed by early October, but we did find a few Wilson’s and large numbers of eared grebes. The phalaropes have an amazing life history in that the females are brightly colored and the dull-colored males incubate the eggs and raise the young. Their feeding behavior is also unusual; they have a long pointed bill which is used to pick up small food items from the surface as they spin around. In the salt lake the food is primarily brine shrimp which are also fed upon by larger birds such as the rare first winter Arctic Sabine’s gull which we observed feeding in a similar manner. At first we thought this was a Bonaparte’s gull which has similar behavior, but the wing pattern during flight showed that this was a Sabine’s, which breeds in the Arctic tundra and winters at sea.
In areas of fresh water inflow we found some western grebes accompanied by a ruddy duck. Their head pattern is similar in that they have a dark dorsal head that includes and obscures the eye, with lighter feathers below. Why is it so important that the eye not be readily visible? Is this primarily to reduce predation on them? Some terrestrial birds seen nearby also had head patterns that obscure the eye. The raucous crow relative, the American magpie, has an entirely black head and neck; in this case the purpose may be not to reduce predation by others but to facilitate capture of prey which might recognize an approaching predator more readily if it had a distinctive eye. The western meadowlark and the juvenile white crowned sparrow both have a dark line adjacent to the eye which would appear to provide some camouflage against predators. It would be interesting to know whether insects respond to the sight of the eye of potential avian predators or just to their movement and body shape. What is clear is that the color and pattern of birds is highly dependent on their natural history and closely regulated by evolutionary selection.
The overwhelming impression you may get in this area is that this very salty and stinky lake which lacks fish (except in areas of fresh water inflow) and any obvious prey supports a vast number of migrant birds. It is a magical place and if you ever are in Salt Lake City I highly recommend a drive on the causeway to Antelope Island to experience the wonder yourself.