Saturday, January 5, 2013

Jan 5, 2013: Erv's Field Notes #51

Ice still thin in some spots on south lake despite the cold temperatures.  12/31/12 (Kelly Poole)

Friday, January 4, 2013, 3 pm. Cloudless blue sky, Southwest breeze, Temperature 27 degrees F.

I parked in the Harrison Street lot and walked around the south lake. I talked to a fisherman who was loading up his ice fishing equipment into his car. He said he drilled two holes in the ice on the south lake and it was only four inches thick. He said that four inches wasn’t safe for an old fat guy, so, he was moving to the north lake where the ice was nine inches thick. I saw several ice fishing groups on the north lake, including two tent shelters.

There is still a large area of open water in the south lake and I estimated 2000 geese and several hundred ducks were spread out around the open water sleeping on the snow covered ice. Most of the ducks were in the water and most of the geese were on the ice. I met up with Wolf Oesterreich and we exchanged notes. He said that the Trumpeter Swan that had been here for the past two weeks was not present today. Besides the Mallards and Canada Geese, other waterfowl present were a couple of dozen Cackling Geese, two Widgeon, and one male Redhead Duck. (We believe this is the same Redhead that showed up with a group of Mallards in November.) Other species observed were Tree Sparrows, Song Sparrows, and American Crows. Wolf reported seeing a Northern Shrike near the north lake as he was making his rounds.

At about 3:30 pm ducks began leaving the lake and flying northwest. A few minutes later, geese began leaving also. Some went northwest and others flew westward. This is the time of day when the flocks go out to find food in the harvested crop fields. A couple of days ago, I saw a large flock feeding in a corn-stubble field north of the park along Hwy 69. I guess enough snow had blown off to expose the corn.

In a previous field note, I mentioned picking up about 20 owl pellets under a cedar tree near the south lake. I have now completed dissecting the pellets. This process is like opening a Pandora’s box because you never know what you are going to find. Owls swallow their prey whole, digest the flesh from the animal and then regurgitate the leftover hair and bones in a large compact wad. The stomach muscles must rotate the pellet for several hours fusing the hair and bones together. Dissection involves teasing apart the hair and bones with a fine forceps. The larger bones of all mammals, including humans, have a distinctive shape. Thus, I was able to sort them out into piles; leg bones in one pile, pelvic and pectoral girdles (scapulae) into one pile, and so on. Smaller bones such as ribs, foot bones and vertebrae are not well represented in the pellets because they are probably broken up into small fragments and digested in the stomach of the owl. The skull is the most important of the skeletal remains because it can be used to identify the species.

In this collection, most of the larger pellets had one or two skulls along with the leg bones and other skeletal parts. The cranium and zygomatic arches around the eye sockets were usually missing because of the grinding action in the owl’s stomach. However, the anterior nostrum, maxilla, and teeth were intact, as were the separate left and right lower jaws. I have not yet counted the number of animals represented in this collection but all were mice except for one small and one large shrew. Species identification will have to wait until I can take the skulls to ISU and examine them more closely under a microscope and compare them with skeletal material in the museum collection. The mice are probably deer mice and harvest mice; the larger of the shrews is probably the short-tailed shrew, Blarina brevicauda and the smaller one is probably the masked shrew, Sorex cinereus. The latter is the second smallest shrew in North America.

Erv Klaas

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