Reading practice 50
NATURAL SCIENCE: Michigan's Beloved Songbird
Sometimes an object in nature is so rare that it escapes mention in nature books. Such is the case of the delightful Kirtland's warbler, a plump.1 yellow-breasted bird that can be found nesting almost exclusively in the northern half of Michigan's Lower Peninsula. Although this bird migrates to the Bahamas for the winter, Michigan is its natural habitat. Unfortunately, so few Kirtland's warblers exist that the species is classified endangered.2 The remaining Kirtland's warblers now enjoy living in stands of young Jack pines located in protected Michigan forests.
Interestingly, the Kirtland's warbler nests on the ground in the jack pine forests, and not in the trees themselves. Male warblers generally return to Michigan in May to spend the summer. Females arrive as the males stake out territory and choose a suitable nesting area. At the completion of the long journey from the Bahamas to Michigan, female warblers begin to collect leaves and grass to build their nests. During this process, the female warblers' mates provide food. Eventually, female Kirtland's warblers cach3 lay four to five speckled eggs. The eggs hatch in two to three weeks, and both the male and female warblers tend to the chicks. Five weeks after they hatch, the fledglings are prepared to survive on their own.
Kirtland's warblers are extremely fastidious about their habitat. This is probably why these birds have become endangered.4 Kirtland's warblers insist on living in expansive areas of Jack pine forest rooted in Grayling sand, which percolates quickly to prevent flooding of nests built on or near the ground. Grayling sand also supports the type of plant material that the warblers prefer for their diet and nest building.
If not for ongoing human conservation efforts.5 this special habitat and this rare bird would probably not exist today. As the massive 19th-century logging boom faded in Michigan, natural forest fires increased. fueled by the burgeoning undergrowth. Jack pine numbers increased dramatically, since the tree depends on regular fires to expose the seeds within its tough cones. The carly6 1900s, though, saw natural fires suppressed by new forest management policies and, consequently. Jack pine forests quickly diminished. 7 reduced the number of nesting areas available for the Kirtland's warbler.
To correct this problem, Jack pine areas are currently managed on a rotating basis. This ensures an appropriate number of nesting sites, which encourages warblers to retur8 and reproduce annually. The protected Jack pine forests are also home to the white-tailed deer, the black bear, the Eastern bluebird, the upland sandpiper. and the snowshoe hare.9 Unfortunately for the Kirtland's warbler, the brown-headed cowbird is also prevalent in these woods. This brood parasite is well known for its tendency to steal the nests of other birds by replacing the original bird's eggs with its own eggs. When the chicks are hatched. the warblers raise the young cowbirds as their own. This, of course, negatively impacts the population of the Kirtland's warbler. Studies have shown that when a cowbird lays one egg in a warbler's nest, generally only one to three warbler chicks will survive. If two or more cowbird chicks survive in a single warbler nest. nonc10 of the warblers will survive. To combat this dilemma. government programs have been established to trap and cradicate11 cowbirds that attempt to nest in the warblers" habitat. These efforts have greatly improved the survival and proliferation of the Kirtland's warbler over the past few decades.
The male Kirtland's warbler is prized as a songbird, emitting a persistent, melodic song audible up to a quarter-mile away. For researchers, counting these songs becomes important during mating season, since saving the warbler from extinction demands an annual census of the population to ensure that conservation measures are effective. Debates12 periodically surface over whether to replace the robin with the Kirtland's warbler as Michigan's state bird. Admirers of the Kirtland's warbler argue that it is strictly a Michigan bird. Supporters of the robin point out that the Kirtland's warbler is only present in Michigan for, at most, halt of the year. Perhaps this debate will continue until more residents have a chance to see the beautiful and elusive Kirtland's warbler, which calls Michigan home.
