For example, multiple petitions to list the northern goshawk (Accipiter
gentilis atricapillus) under the Endangered Species Act of 1978 as a
Threatened or Endangered Species in the western United States prompted
several studies of their nesting habitat (Kennedy 1997; DeStefano 1998).
One pattern that emerged from these studies is that goshawks, across a
broad geographical range from southeastern Alaska to the Pacific
Northwest to the southwestern United States, often build their nests in
forest stands with old-growth characteristics, i.e., stands dominated by
large trees and dense cover formed by the canopy of these large trees
(Daw et al. 1998). This pattern has been verified, and the existence of
the pattern is useful information for the conservation and management
of this species and its nesting habitat. However, because these
studies were observational and not experimental, we do not know why
goshawks nest in forest stands with this kind of structure. Some likely
hypotheses include protection offered by old-growth forests against
predators, such as great horned owls (Bubo virginianus), or unfavorable
weather in secondary forests, such as high ambient temperatures
during the summer nesting season. An astute naturalist with sufficient
time and energy could have detected and described this pattern, but
the scientific method (including hypothesis testing) is required to answer
the question of why. Knowledge of the pattern increases our information
base; knowledge of the mechanism underlying the pattern
increases our understanding (Figure 1.1).
For example, multiple petitions to list the northern goshawk (Accipiter
gentilis atricapillus) under the Endangered Species Act of 1978 as a
Threatened or Endangered Species in the western United States prompted
several studies of their nesting habitat (Kennedy 1997; DeStefano 1998).
One pattern that emerged from these studies is that goshawks, across a
broad geographical range from southeastern Alaska to the Pacific
Northwest to the southwestern United States, often build their nests in
forest stands with old-growth characteristics, i.e., stands dominated by
large trees and dense cover formed by the canopy of these large trees
(Daw et al. 1998). This pattern has been verified, and the existence of
the pattern is useful information for the conservation and management
of this species and its nesting habitat. However, because these
studies were observational and not experimental, we do not know why
goshawks nest in forest stands with this kind of structure. Some likely
hypotheses include protection offered by old-growth forests against
predators, such as great horned owls (Bubo virginianus), or unfavorable
weather in secondary forests, such as high ambient temperatures
during the summer nesting season. An astute naturalist with sufficient
time and energy could have detected and described this pattern, but
the scientific method (including hypothesis testing) is required to answer
the question of why. Knowledge of the pattern increases our information
base; knowledge of the mechanism underlying the pattern
increases our understanding (Figure 1.1).
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