WASHINGTON – The fortunes of its orange-and-black-clad baseball namesakes may be on the rise, but those of the Maryland state bird are on a steady decline.
There are about 24 percent fewer Baltimore orioles in Maryland today than there were 30 years ago, when accurate records started being kept, and the rate of decline throughout the region is increasing, government data reveal.
While the Baltimore oriole is by no means on the verge of extinction, its consistently decreasing numbers do not bode well for the colorful songbird’s future.
“It’s not at the point where it’s going to be listed as endangered, but if this trend were to continue over a period of time, it could,” said Bruce Peterjohn, the coordinator of the Breeding Bird Survey, which began tracking bird populations in 1966. The survey is coordinated each year from the Patuxent Environmental Science Center in Laurel, Md.
The annual rates of population decline in the region from 1966 to 1994 range from “significant,” such as New Jersey’s 3.9 percent yearly drop, to “slight,” such as West Virginia’s .7 percent, the National Biological Service’s Breeding Bird Survey results show.
The average annual rate of decline in Maryland from 1966 to 1994 was .8 percent, the Breeding Bird Survey records show.
The rate of decline has been sharpest in recent years. In Maryland, the average annual rate of decline has been 1.9 percent since 1980. That’s more than six times the rate of .3 percent from 1966 to 1979.
“Orioles are a lot scarcer,” said Douglas Gill, a University of Maryland zoology professor and an avid birder.
“It [used to be] that from mid- to late April through the summer it would be surprising not to see one,” said Gill, who has been bird watching in the area since he moved here in 1971. Now, he said, “there’s an increasing number of days you miss seeing one.”
The migratory bird survey determines population trends by sending skilled volunteers each year to more than 2,750 roadside routes across the United States and Canada on one day during breeding season. It’s usually a day in May or June.
Trends are calculated by comparing the most recent year’s bird counts to previous years’.
With the exception of birds near extinction, the actual number of birds in a species is incalculable, said Peterjohn.
No one knows for sure what is causing the Baltimore oriole population to decline, said Doug Gross, a senior environmental biologist for Ecology III, a private environmental consulting firm.
“It seems like the decline of the Baltimore oriole is a bit of a mystery,” Gross said.
Scientists said they have several suspicions, however.
For instance, the bird’s habitat is slowly disappearing.
Baltimore orioles prefer to hang their bag-like nests from shade trees, particularly elms.
In 1930, Dutch elm disease, a fungus infection, was introduced in the United States from Europe. Across North America, the disease decimated elms and the birds virtually disappeared from elm-lined suburban neighborhoods, Gill said.
The Baltimore oriole’s range extends from Louisiana and northern Georgia to Nova Scotia and Alberta, Canada. The bird continues to lose breeding grounds in its range when suburbs encroach into farmland and tract houses replace rural areas, the biologist Gross said.
“Development alone could account for a 1 percent drop,” he said.
Also, the food supply may be tainted.
Orioles are particularly sensitive to pesticides, Gill said. Caterpillars, such as gypsy moth larvae, are a main source of food for the Baltimore oriole and a main target of pesticides.
When the insects have been sprayed with pesticides, birds that eat them are ingesting poisons in increasingly magnified doses, he said. Many birds of prey, such as bald eagles, ospreys and peregrine falcons, were nearly wiped out in this way when their food supply became tainted with the chemical DDT in the 1950s, ’60s and ’70s.
“If each caterpillar has one drop of pesticide in its hair, and an oriole eats 100 caterpillars, then the oriole has had 100 doses,” Gill said. “We’re all familiar with the DDT story. It’s now taken 20 years for them to recover.”
Interestingly, the population recovery of large birds of prey could be a factor in the decline of songbird populations.
“The skies now are filled with bird predators, like hawks. And what do hawks like to eat? Birds like orioles and scarlet tanagers,” Gill said.
In addition, the Baltimore oriole is a Neotropical migrant, spending winters in Northern Mexico and Central America. The root of the problem could be found there.
“I would point the fickle finger of fate at Mexico and Central America, with their use of pesticides and forest fragmentation,” Gross said.
Many Neotropical migrant species are declining, he said, and deforestation and the “heroic amounts” of pesticides used in that region may be the common causes. Yet there has been little research about the wintering habits of the bird, Gross said, so there is no data to support or refute that hypothesis.
The oriole’s dwindling numbers are not being ignored by state officials.
“We are well aware of the population trends of the Baltimore oriole and other Neotropical migrant breeding birds in the state,” said Glenn Therres, an ornithologist for the Maryland Department of Natural Resources. He said the state tracks bird populations using data from the Breeding Bird Survey.
Maryland does not have programs geared specifically toward saving the Baltimore oriole, but it is taking part in international neotropical migrant conservation efforts, Therres said.
Recent laws requiring that new suburban developments meet forest preservation guidelines will indirectly benefit all of the state’s Neotropical migrants, Therres said. For more information on the Baltimore oriole and other migratory birds, check the Internet at: http://www.mbr.nbs.gov/ -30-