Sunday, February 20, 2011

The White Choir: Light Geese

Waterfowl at dawn - Bosque Del Apache National Wildlife Refuge. All images in this post by David Powell.

“In complete darkness long before sunrise, you know that you are surrounded. The sound of the white choir crescendos, rising in intensity and volume until it floods your senses. As night gives way to day, the sensation transforms from audio to visual.” John Vradenburg, supervisory biologist at Bosque del Apache National Wildlife Refuge, shared his passion for the wintering waterfowl and Sandhill Cranes that are the signature birds of the refuge.

Light Geese, as they are referred to by biologists, are actually two different goose species, Snow Goose and Ross’ Goose. The Snow Goose is a medium-sized goose with a distinctive blackish “grinning patch” or “smile”, while the Ross’ Goose is smaller and lacks the grin patch. Most adults of both species are completely white except for some gray under the wings and black wingtips.

Light geese breed colonially in subarctic and arctic tundra near the coast on featureless terrain near ponds, shallow lakes, streams, or islands in braided deltas. Some high arctic colonies are located well inland on rolling terrain, exposed slopes of ravines, and cliff edges, but most nest in low-lying wet meadows with plenty of sedges and grasses. The preferred nesting areas are clear of snow early in the season and not flooded during spring thaw.

Bosque del Apache NWR hosts about 45,000 of the two goose species each winter. They begin showing up in mid-October and stay until mid-March. The population peaks in late November through early December when migrants that will settle further south at wetlands in Mexico, stop here to rest and refuel. In the Middle Rio Grande Valley, populations appear stable, although numbers of light geese nationwide are millions beyond carrying capacity, according to Vradenburg. Overpopulation makes the birds susceptible to disease on wintering grounds and increases competition for nest sites and food resources on the Arctic tundra.

Parents stay with their young throughout the first winter. Families travel together on both the southbound and northbound migrations, separating only after they return to the arctic breeding grounds. Family groups can easily be seen in migrating and wintering flocks and, amazingly, manage to remain together even when landing in the midst of a densely packed raft of floating geese at roost sites.

Light goose hunting was banned in parts of the United States in 1916 due to low population levels. Hunting was allowed again in 1975 after the population had significantly increased. Today, hunting mortality, despite liberal bag limits, has so far failed to curb the 5% annual growth of most populations. Some populations have grown so large that the geese are destroying their nesting habitat.

Light Geese did not always winter in the Middle Rio Grande Valley, but began showing up in the 1960s and 1970s. Vradenburg thinks the geese always flew over the valley but wintered in the highlands and central valley of Mexico, and along the Gulf coast. As more managed wetlands and reservoirs in Colorado created desirable roosting and foraging habitat, the population shifted. Bosque del Apache happened to be in the right spot for the geese and other birds to stop over.

There is a blue morph of both species also occurs in about 10% of the population. The dark color of the blue morph is controlled by a single gene, with dark being partially dominant over white. If a pure dark goose mates with a white goose, the offspring will all be dark, except for a possible white belly. If two white geese mate, they have only white offspring. If two dark geese mate, they will have mostly dark offspring, but might have a few white ones too.

Bosque del Apache was established in 1939, for the purpose of providing habitat for migratory and breeding water birds. Before it became a wildlife refuge, it was mesic (wet) floodplain habitat with farmland and upland areas. Then, more natural conditions existed since the river had not yet been controlled. The refuge was developed when the levee was moved to control annual spring flooding and confine the Rio Grande. After the low flow channel was created, the refuge had to install and intensively manage the wetlands we see there today.

“Heard long before they are seen, they let us know that that the migration season is upon us."

The Bosque and the Snow Geese, in particular, are a multi-sensational experience that combines the mass of thousands of geese, audio and visual, where you can literally lose your voice to the cacophony of mass of white flight,” reports the enthusiastic Vradenburg of the experience of visiting one of the premier wildlife refuges in the United States.

At only $5/car, it makes for an impressive and entertaining winter day trip, only 120 miles south of Jemez Springs. If you go, plan to depart late morning, stopping at one of the local eateries for lunch, and arriving at the refuge in early afternoon. Be sure to stay for evening fly-in when the geese, cranes and ducks return to their roost sites for the night. You’ll be glad you stayed to hear the night choir.

Friday, February 11, 2011

Marsh Hawk: Northern Harrier

A juvenile Northern Harrier tries to defend a fish carcass from an adult female. All images in this post by Doug Brown, except the final image.

Perched atop the limp body of a dead snow goose lying among the grasses in shallow water, the slim-bodied raptor yanked out yet another tuft of white feathers. The brown feathers that characterize female and young Northern Harriers stood in stark contrast to the brilliant white of her prey. Yank! More feathers flew! My friend asked how in the world this medium-sized raptor could have brought down an animal more than three times its own size. Yank! White down floated through the air. I explained about the opportunistic nature of all raptors, taking food that is easy versus fresh. Yank! White fluff surrounded the two birds. Perhaps the snow goose died of natural causes. Yank! I wondered if the diligently plucking hawk would ever reach the flesh of the goose. Yank, yank! Would a hungry Bald Eagle notice the growing pile of white that surrounded the brown? Surely, the harrier, weighing less than two pounds, would be no match for a predatory bird five times its size. Yank! We never knew the final outcome. Eventually, we tired of watching the slow motion drama, and moved on to another area, leaving the bird to her feast.

Not just vultures, known for their scavenging habits, but all raptors and almost all species of predatory animals are opportunistic feeders. Although hawks, eagles and falcons all take live prey, they also scavenge, steal from others and, in general, get food the easiest way possible. At crowded winter roosts, birds can easily spread disease, particularly among waterfowl that gather by the tens of thousands in a single pond. Avian cholera may very well have been the final straw for the goose that had flown south from its Arctic breeding grounds.

Adult male Northern Harrier.

Formerly known as the marsh hawk, the northern harrier hunts primarily on the wing and may cover up to 100 miles per day. Its normal prey, consisting mostly of rodents and small birds, is detected using extremely sharp hearing, facilitated by a pronounced facial disk that helps to direct sound toward its ears. Long yellow legs help it to snatch prey from tall marsh grasses. Commonly seen soaring low to the ground, coursing back and forth over marsh, field, or pastureland, the harrier holds its wings in a shallow “V”, also called a dihedral. The slender-bodied hawk has a long tail and wings, and a conspicuous white rump patch, making it one of the easier hawks to identify.

However, males and adult females are strikingly different. The males are a gorgeous shade of blue gray on their backs, white below with black wingtips, and lemon yellow eyes. Females and young of both sexes are similar with brownish backs, buff-colored undersides which are streaked in the adult females and solid in the juveniles. Males often tend to be found in more upland habitats, whereas females and young frequent lowland areas and marsh habitats.

Adult male Northern Harrier viewed from below.

The northern harrier is found worldwide. There are estimated to be more than 111,000 individuals in North America, breeding primarily in dense, tall marsh grasses, hence their common name, Marsh Hawk. The scientific name is Circus cyaneus which is derived from the the Greek words kirkos, meaning a circle, a reference to the bird flying in circles, and cyan, a blue color referring to the color of the male bird. Harrier is from the Old English word hergian, which means to harass, ravage, or plunder.

Harriers roost and nest on the ground, often in groups in a traditional location. Most males are mated to one or two females at the same time. Some males pair with up to five mates in a season. Females incubate the eggs and brood the offspring, while the male provides the bulk of the food for his mates and their nestlings.

Female or juvenile Northern Harrier, showing the prominent white rump patch.

Historic populations were considered abundant and widespread, but declines have been observed in recent decades. In 1972, this species was placed on the American Birds' Blue List and has remained there since. Declines were primarily due to a loss of breeding habitat and the effects of pesticides. Reforestation, filling in of wetlands, changes in land use, and urban and industrial development in coastal areas all contributed to habitat loss.

During the early-mid 1900s, rampant shooting of all raptors, then considered vermin, also contributed to declines. Attitudes changed and raptor persecution subsided, particularly for the littlish hawk known for dining on the small rodents so disliked by most humans. Subsidence; however, does not spell an end to raptor persecution, still practiced but relegated to shadowy corners.

Photo by Pete Jungman, a falconer in southern New Mexico.

It was 2009. I received a photo of a beautiful male harrier, shot dead; its lifeless body hung on a fence right next to a sign that said “no hunting”. A littlish raptor, minding its own business, helping to keep our rodent population in check.