ACT
Practice Test 32

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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 with the delightful Kirtland’s warbler, a plump, yellow-breasted bird that can be found nesting almost

Line 5 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. The remaining Kirtland’s

10 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

15 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

20 this process, the female warblers’ mates provides food. Eventually, female Kirtland’s warblers each 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

25 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. Kirtland’s warblers insist on living in expansive areas of Jack pine forest rooted in

30 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,

35 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

40 regular fires to expose the seeds within its tough cones. The early 1900s, though, saw natural fires suppressed by new forest management policies and, consequently, Jack pine forests quickly diminished. This greatly reduced the number of nesting areas available for the

45 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 return and reproduce annually. The

50 protected Jack pine forests are also home to the whitetailed deer, the black bear, the Eastern bluebird, the upland sandpiper, and the snowshoe hare. Unfortunately, for the Kirtland’s warbler, the brown-headed cowbird is also prevalent in these woods. This brood

55 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

60 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, none of the warblers will survive. To combat this dilemma,

65 government programs have been established to trap and eradicate 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.

70 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

75 census of the population to ensure that conservation measures are effective. Debates periodically surface over whether to replace the robin with the Kirtland’s warbler as Michigan’s state bird. Admirers of the Kirtland’s

80 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, half of the year. Perhaps this debate will continue until more residents have a chance to see the beautiful and elusive

85 Kirtland’s warbler, which calls Michigan home.

In the context of the passage as a whole, it is most reasonable to infer that the phrase “jack pine areas are currently managed on a rotating basis” (lines 46–47) means that:

  • Solution

    The best answer is B. According to the passage, jack pine “depends on regular fires to expose the seeds within its tough cones.” It is likely that any management of the forests would include periodic, supervised burning in order to encourage new growth.

The passage suggests that the population of the Kirtland’s warbler declined in the past because forest management policies:

  • Solution

    The best answer is F. The passage states that, “The early 1900s, though, saw natural fires suppressed by new forest management policies and, consequently, jack pine forests quickly diminished.” These fire prevention policies stopped all fires, most likely because of the destructive threat they pose to land, buildings, and infrastructure. An unforeseen consequence (“externality”) was the depletion of fire-dependent jack pines, which constitute the exclusive habitat of the Kirtland’s warbler.

What does the passage offer as evidence that Kirtland’s warblers have environmental sensitivities?

  • Solution

    The best answer is D. The passage states that the warblers are “extremely fastidious [picky] about their habitat.” Subsequent paragraphs describe historical strain on Jack pine forests which host the birds. Answer choices B and C are never said to be detrimental to the success of the bird. Answer choice A, while detrimental, is coincidental to the birds’ renewed proliferation among the jack pines. The principal reason that the bird is endangered is the widespread decline of suitable habitat.

It can be inferred that the author feels Michigan, not the Bahamas, is the Kirtland’s warbler’s natural habitat because the birds:

  • Solution

    The best answer is J. The passage states that the Kirtland’s warbler “migrates to the Bahamas to winter.” This suggests a temporary stay, much like how people in the United States may winter in Florida, but still call their northern residence home. The warbler engages in its most complex behavior while in Michigan (i.e., building nests and mating), which best supports answer choice J.

According to the passage, what is the reason jack pine forests declined in the early 1900s?

  • Solution

    The best answer is C. According to the passage, forest policy at the turn of the century dictated that all fires should be prevented; as a result, Jack pines, which require fire to reproduce, suffered, which best supports answer choice C.

What does the author suggest in lines 54–55 by stating that the cowbird is a “brood parasite?”

  • Solution

    The best answer is F. The word “brood” describes the group of eggs a bird raises at one time. Thus a “brood parasite” is an organism that preys on the nestling of another bird.

The passage states that the habitat needs of the Kirtland’s warbler, as compared to those of other birds, are:

  • Solution

    The best answer is B. The fact that the passage claims that Kirtland’s warblers are “fastidious about their habitat” indicates that their habitat requirements are uncommonly rigid as compared to other birds, which best supports answer choice B.

According to the passage, which of the following correctly states the relationship of the Jack pine to fire?

  • Solution

    The best answer is F. The passage states “the tree depends on regular fires to expose the seed within its tough cones.” This indicates the cones are ready prior to the fire, eliminating answer choice G. Answer choices H and J are not supported by the passage.

The author states that the main reason for the Kirtland’s warbler’s decline is:

  • Solution

    The best answer is C. The Jack pine problem is cited as the major contributing factor to Kirtland’s warbler decline. These trees are the bird’s habitat. Answer choice D might appear to be correct, but the logging of jack pines is not cited as a reason for the widespread depletion of the tree; fire prevention is.

As it is used in lines 30–32, the term Grayling sand most nearly means:

  • Solution

    The best answer is G. The word “percolates” means “drains” in the context of soil, indicating it is “permeable.” This is important to prevent flooding of nests. The passage continues by indicating that Grayling sand supports the plants that the Kirtland’s warbler requires.

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