In many areas of human activity, the things people do for one reason may have a second, unintended byproduct. All too often that byproduct is a threat to the environment or wildlife. Two examples of this that have recently come to light include bushes planted along highways and a chemical used in birth control pills and hormone replacement therapy.
The bush in question is the elaeagnus, also known as the silver berry bush. It has been promoted as ideal for highway medians since the 1960s for its tall, dense foliage that reduces headlight glare from oncoming cars. It is used widely along highways from Virginia to Florida. The problem is that it is also an ideal bush for attracting cedar waxwings.
The elaeagnus is not a native plant and doesn't behave like one. Originally from Japan and China, it blooms from October through November and bears fruit in April and May. Hungry waxwings, eager to build up fat reserves, are migrating north to their breeding grounds just as the bushes are exploding with fruit.
Splat. An ornithological catastrophe. Thousands and thousands of cedar waxwings are hit by cars while foraging for this berry along highways throughout the southeastern United States.
Compared with leftover holly berries, buds and insects, the plump elaeagnus fruit along the highway calls out like the neon lights of a diner. The waxwings fare worse that other fruit-eating birds because they travel in large flocks and descend by the hundreds in a small area.
In the Lee Hall area of Virginia, which has one of the longest stretches of elaeagnus bushes in the state, researchers picked up more than 1,200 birds during one week last spring. It's estimates that the number actually killed is much higher because most of the collisions don't leave any trace of the bird.
The researchers said there was only one solution to the problem. The bushes must go. The Virginia Department of Transportation is complying. The removal project will cost up to $75,000. Virginia is the first state to investigate the birds-and-berries problem, and do something about it.
Another example of human activity endangering wildlife is oestrogens, which is used in birth control pills or hormone replacement therapy for women. Researchers have been finding traces of it in streams and rivers. The chemicals could be causing problems for songbirds.
Researchers know they can change the brain circuitry of female zebra finches by injecting them with oestrogen shortly after birth. This makes them sing, normally the preserve of males. Researchers wondered whether the birds would also be affected by eating doses of oestrogens similar to those they would ingest in the wild.
Hatchlings were fed for a week with food containing oestradiol, an oestrogen used in hormone replacement therapy. When the birds grew into adults, the researchers found that female finches fed on oestradiol started to sing, as did the males.
The birds' ability to reproduce was also severely affected. Finches given oestradiol produced fewer eggs and they had brittle shells. The number of hatchlings fell dramatically.
This problem still needs to be studied in wild bird populations.
