Muskrat

I encountered three muskrats on one of our last, warm November afternoons.  Muskrats feed mainly on aquatic vegetation.  They are not dormant during the winter, and must eat every day. Muskrats, rats and mice belong to the same family.  Muskrats owe their name to their musky scent glands with which they mark their territories.

Muskrat populations expand and contract through a 6 to 10 year cycle. The muskrats in this photo are likely a family group. They burrow in bank-sides of lakes or streams or they build lodges with underwater entrances.  Muskrats also build platforms for feeding.

Sharp-shinned Hawk

Because this forest-inhabiting hawk subsists almost entirely on small birds, this Sharp-shinned Hawk was probably attracted by the activity at our feeders.  I banded it on 8 November.  The hawk flew up from our water feature, where it may have been drinking.  At the time, no small birds were evident.

Male Sharp-shinned Hawks are much smaller than the females.  The size of the sexes do not even overlap.  This bird, with a wing chord of 203 mm, is a female.  Her yellow eye and brown back indicate she is a young bird.

Several hypotheses exist to account for female hawks being larger than their mates. Perhaps females need to be larger to protect themselves from dangerous, aggressive males. Alternatively, perhaps to reduce competition between the sexes, males and females specialize in different sized prey. Apparently, for whatever reason, the more a raptor specializes in taking small birds, you expect to see a larger difference between the size of the sexes.

Cackling Goose

While taking photographs of Canada Geese (see first photo) in the Cannon River within the city of Northfield, I noticed that about a quarter of the flock were smaller and tended to stay away from the larger geese.  The smaller birds' bills are relatively shorter and stubbier, giving the bills a triangular appearance (see middle photo).   Additional field marks add up to the small birds being Cackling Geese. 

1. In the photo at the end of this post, a Cackling Goose swims in front of two Canada Geese.  The head is not as round as in the middle photo above, but not as wide as in the Canada Goose.  (The Cackling Goose in the bottom photo shows kind of a squarish, rather than round, head--but that is OK.)

2. The forehead of the Canada usually has more of a slope to it than does the more angled Cackling forehead.

3. The Cackling Goose tends to have a relatively shorter neck--a field mark that is apparent in the lower photo, but murky if the bird is stretching its neck out as in the middle photo.

4. Cackling Geese show slightly darker breasts than do Canadas, a mark that can be seen in the photo below. 

Until recently, Cackling Geese were considered to be a small race of the Canada Goose.  Genetic studies indicate that the two forms are distinct species.  Paul Hertzel, Ross Silcock and Stephen Dinsmore have published a website that further discusses identification issues with these geese. They warn that not every Cackling Goose, especially when solitary, is easily identified.

Tundra Swan 2

Do any field guides depict ducks dappling?  For today's quiz, name these ducks!   The swan is not difficult.  Its meter-long neck allows the Tundra Swan to feed in relatively deep water on plant stems and roots.  Often the feet are used to dig up plants. This swan also feeds in agricultural fields in the winter and arctic meadows in the summer (Limpert and Earnst 1994).

Moments after I took the photograph above, all three waterfowl came up for a breath--and I took the next photo.  You can see the answers to the quiz--Tundra Swan, Mallard, and Northern Pintail.  This post is the last from our trip to Brownsville, Minnesota. For finding birding spots in Minnesota, Kim Eckert's A Birder's Guide to Minnesota is indispensable.

Bald Eagle 3

Most of the eagles we saw on Friday were not in adult plumage (you may recall that Bald Eagles take four years to attain their black and white plumage).  Bald Eagles are sometimes confused with Golden Eagles.  But Bald Eagles have arrow dark bands at the ends of their tails and lack distinct white patches on their upper wings. All the eagle photos on this post are of Bald Eagles.

The eagles appeared to play.  Individuals swooped and tumbled with each other. This sort of behavior prepares them with survival skills. A couple of young eagles made passes over a flock of Common Goldeneyes.  Bald Eagles, when they are not scavenging dead prey, often hunt by soaring.  Their soaring capture rates are low.  We wondered if our birds were just testing the goldeneyes to see if any one of the flock was wounded.

Bald Eagle 2

Dozens of Bald Eagles were almost as exciting as Tundra Swans during our Friday road-trip.  The Bald Eagle's recovery is one of our premier environmental management successes.  Their populations plummeted due to persecution (Alaska offered a bounty on Bald Eagles) and lowered reproduction from DDT contamination.  This species' rebound is such that by the late 1990s, Bald Eagles now breed across Canada and in all the contiguous states except Rhode Island and Vermont (Buehler 2000).

Bald Eagles are monogamous and thought to mate for life unless a mate dies. Pairs apparently stay together throughout the year. One problem with studying Bald Eagles, however, is that banding adults is difficult.

Tundra Swan 1

On Friday Erika and I took a road-trip to extreme southeastern Minnesota, just south of Brownsville.  We hoped to see flocks of Tundra Swans.  We had no trouble finding the swans.  Just south of Brownsville, the Fish and Wildlife Service has built two overlooks just where the swans are most easily seen.  We saw hundreds.

Tundra Swans breed in arctic Canada and Alaska and winter either in the Pacific Northwest or in the Chesapeake Bay region.  Swans heading towards the bay fly across much of the northern Great Plains.  These birds rest up and refuel near Devil's Lake in North Dakota and in the upper Mississippi Valley in southeastern Minnesota.  They leave the arctic in late September and arrive in Minnesota in early October.  They leave here and make a non-stop migration to the Chesapeake (1600 km), arriving on the East Coast from mid-November through December.  (Western Swans rest in Utah, before proceeding to California and Oregon.)

Tundra Swans migrate in family groups within flocks that can be over 100 birds. Before mating at 2 or 3 years, young swans may "date" other swans.  Once mated they are monogamous and remain together all year.  Divorce is rare, although presumably they will remate if one of the pair dies. (Much of this information is from Limpert and Earnst 1994).

Pileated Woodpecker

Some readers my recall my 5 November 2009 entry in which I posted a gif of a Pileated Woodpecker giving me a hard time. My hands were also bloodied after banding this first-year male bird.  I was glad, however, to add this species to my series of white-background photographs.  I use white mat board as background when I take the pictures (although I was first inspired by taking photos of birds in front of snow drifts last winter).

Pileated Woodpeckers depend on large trees for breeding.  This dependancy becomes critical if large trees are cut out of forest stands.  Pileateds breeding in our backyard had their tree fall in the 2009 winter during a windstorm.  The birds must still be in the vicinity, since this Pileated in the second bird-of-the-year I have banded in 2010. Large trees also attract lightening (especially when surrounding trees are smaller), sometimes to the woodpeckers' detriment. Large trees come at such a premium, that pairs defend their territory all year.  Individuals do not abandon territories if their mates die.  Pileateds are also often hit by cars, since the woodpeckers often feed on or near the ground.  Despite these dangers, Pileated Woodpecker populations appear to be increasing since the mid-1960s (Bull and Jackson 1995).

Hooded Merganser

Hooded Mergansers are among our most handsome ducks.  For the past few falls, I have been aware of a small flock inhabiting a lake next to Spring Creek Road in Parmeadow Park near one of Northfield's golf courses.  With high traffic, both pedestrian and automobile, these birds are relatively tame.

Other mergansers survive almost entirely on fish.  Hooded Mergansers capture more diverse fare, including fish, insects, and crayfish.  Although acid rain is a threat to many breeding populations, Hooded Merganser populations are healthy (Dugger et al. 2009).

 

I have previously witnessed this behavior in other male Hooded Mergansers.  The birds rear and flap their wings after surfacing from dives.  They may be drying themselves or, perhaps, signalling their location to other surfacing flock members.

Bald Eagle

On Friday, Erika and I birded locally.  We flushed this Bald Eagle as we drove around a corner on the north edge of the Carleton College Arboretum along Little Canada Road.  The eagle briefly perched atop a nearby pine, but then flew away. 

"That would have made a good blog entry," remarked Erika.  "Not without a photograph." I replied.  About 20 minutes later, we returned to the same spot.  We found the eagle perched in a large oak and I was able to take one photograph before the bird again flew. 

Bald Eagles require four years to obtain their striking adult plumage. During these years, the eagles continually molt, and so continually change their appearance. According to the description is the Peterson Field Guide Series, Hawks, our bird is probably a second-year bird. This book is a decent field guide to birds of prey and can be obtained through the accompanying link at bargain prices. (Two volumes by Brian Wheeler may be better, Raptors of Western and Eastern North America, but they are expensive.  Minnesota is covered in the Western volume.)

The eagle was feeding on an opossum carcass. I assume the opossum was road-kill and that the eagle was scavenging. A cursory search of the literature finds no mention of Bald Eagles consuming opossums.  Eagles are primarily fish-eaters, but are known to take a wide variety of prey when fish are not available.  Arthur C. Bent, in his monumental masterpiece Life Histories of North American Birds of Prey, wrote, "As eagles do not disdain carrion, they may often be seen...feeding on the carcasses of any animals they can find.." This 26-volume set of books is now somewhat dated, but still contains a wealth of information.  The books were first published by the Smithsonian and then reissued as Dover reprints. Prices for these books vary greatly, so some research is advised if you are interested in obtaining them.

If you are interested in up-to-date life histories of birds, the American Ornithologists' Union's Birds of North America is now a continually evolving, on-line resource.  Subscriptions to the series are pricey, but free to AOU members!  Some libraries have copies of the print version of Birds of North America, but they do not appear to be available through Amazon.