Water Birds and Drought

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August is a time of transition for birds in the temperate and subpolar regions of the Northern Hemisphere. The Earth on its tilted axis has been moving around the Sun toward the equinox, when the days and nights will be of equal length down in the tropics. Up here in the higher latitudes though, the days have been getting shorter since June 21, and the birds have been paying attention.

Many species in the field and woods behind our cabin are still feeding fledglings and many of them have stopped singing altogether—I haven’t heard a chestnut-sided warbler since the third week of July—or are singing less often and differently. The scarlet tanagers are still singing and when I can find one up in the canopy, I check to see whether they have begun molting. I haven’t seen any patches of green yet.

Further to the north, the breeding season has been over for some time. Although this is a part of the Earth that is warming rapidly, the weather is also becoming very irregular. The shorebirds and waterfowl that nest up there in the tundra may have more time, but that time is now more likely to be marked by unusual rain events or drought with the consequent flooding or fire.

Another region that has been seeing more extreme weather events is the Great Plains and the intermontane West of the United States and Canada. I have been trying to get hold of a New Hampshire forester to interview him about Class VI road use during logging, but he may already be out west fighting fires, as he is also a fire jumper. There are so many fires out there now that the western states don’t have the personnel to contain them on their own. Eastern firefighters are flown out to help.

Much of the country from the Mississippi River to the west coast is now in drought. The rivers are going dry and the reservoirs are emptying. This is not a new phenomenon out there; it is simply getting worse. A 2010 paper by Thomas Albright (Univ. Wisconsin, Madison) and others used Breeding Bird Survey data to examine the effects of drought between 1989 and 2005. Migratory species in semi-arid regions (e.g., the Great Plains) were most strongly affected. Generally speaking, however, the researchers found the birds to be both resilient (they recovered quickly after the drought ended) and resistant (their numbers did not fluctuate greatly, especially

resident birds) to environmental change. However, Albright et al. noted that while birds were adapted to some degree of fluctuation, unprecedented extreme conditions in Europe had had a significant impact on bird communities there.

The grebes are a family (Podicipedidae and order Podicipediformes) strongly associated with the Great Plains and intermontane West. Drought is particularly problematic for them because almost entirely aquatic and dive for fish and invertebrates in the lakes and marshes where they live and breed on nests made of mats of floating vegetation. The legs are placed so far back on their bodies that they push themselves along on their breasts on land.

We have seven species in North America, but only one of them, the pied-billed grebe (Podilymbus podiceps), breeds east of the Mississippi, including here in New Hampshire. “Pied” means having two colors or more. The pied-billed grebe has a white bill with a black ring around it (the white of the male’s bill is light blue during the breeding season). It is otherwise a brown bird, darker above and lighter below, a little over a foot long.

It is found from coast to coast in small ponds. While generally common, they are very sensitive to being disturbed and will abandon their nests quite easily. Motorboat wakes can also easily swamp their floating nests. They are not common in New Hampshire. The Atlas of Breeding Birds in New Hampshire attributes their scarcity to habit loss. “Dredging and filling have destroyed numerous wetlands, while pollution and contamination have affected many others. Water level fluctuations on dammed ponds and increased predation may be factors in New Hampshire.”

Several of the grebes of the west face similar threats. The numbers of the horned grebe (Podiceps auritus) have declined by 79% in North America over the last 30 years. It is still a relatively abundant bird, but the International Union for Conservation of Nature (IUCN) has recently shifted its status to “vulnerable.” Like the pied-billed grebe it breeds on small ponds, but between western Ontario and Alaska. The declines in its populations there are reported to be due to “human disturbance, forestry operations around breeding sites, fluctuating water levels, and stocking of lakes with rainbow trout that compete for aquatic insects.” Happily, this trend seems to have reversed since 2005.

The western grebe (Aechmophorus occidentalis) has been slowly declining in numbers over the past two decades. These large birds (25 inches long) live in large ponds, lakes and marshes and are famous for their acrobatic courtship dance. Since 2005, CBC (Christmas Bird Count)

numbers have ranged between approximately 55,000 to 95,000 individuals, a decline of ~50% from previous decades. The IUCN, however, is not concerned about the species’ status.

The Christmas Bird Count numbers are of wintering individuals. Most grebes winter in marine environments where they are susceptible to oil spills. Some western species migrate eastward and winter on the Atlantic coast. The Birds of New Hampshire lists four species in addition to the resident pied-billed. Two are regulars: the horned grebes arrive in the second half of October, the red-necked in late November. Eared and western grebes visit only rarely. The horned and red-necked are occasionally seen on inland lakes, but much more reliably around the Isles of Shoals. Our resident pied-billed grebes will begin migrating to the southern U.S. later this month.