11. Avian Communities in Temperate Rainforests
237
The results for canopy seed predators, indicating a higher frequency of
species and individuals in Chiloe than Alaska (parts A and B, Table
11.2), is at least partly an artifact. Many of the seed predators of the
North American conifer forest are sporadic and even nomadic in occurrence and often do :not breed during the season used by most birds for
nesting (Benkman ; personal communication). Therefore, they are not
often recorded in spring "breeding-bird" censuses and are certainly
underestimated in this study (especially Loxia species).
We compared guild structure of the Chilean bird community to that of
Alaskan coastal forests and that of Canadian interior forests to the east of
the coastal range of mountains near Juneau to determine if the bird
communities of the two rainforests (Alaska coastal, Chiloe) are convergent in structure. The guild structure of Chilote forest birds is no more
similar to that of Alaskan coastal forests than it is to that of Canadian
forests. The proportionate frequency of species in Chiloe is most similar
to Alaskan forests (specifically conifer forests) for three guilds (big-tree
users, understory birds, leaf-gleaners), and most similar to Canadian
forests of the remaining three guilds (covered nesters, aerial feeders,
canopy seed predators), as shown in Table 11.3. This result suggests that
guild structure of the Chilote forest birds is not particularly similar to that
of Alaskan coastal forest birds.
Comparison of Guild Structure in North and South
Temperate Forests
Patterns
Data from our censuses were combined with data extracted from published
studies, and classified by location (northwest North America, midwest
North America , south temperate) and forest type (broadleaf, conifer).
The resulting six categories were subjected to two-way ANOVA , in a
search for general patterns. Because we already know that there is some
heterogeneity within the northwest region (i.e., between Alaskan coastal
and Canadian interior forests) , this exercise serves chiefly to look for
patterns on a continental scale. Where direct comparisons of these results
with those of the preceding section yield different results, that difference
may reflect the difference in scale and perhaps point to interesting exceptions to generalizations .
Broadleaf forests consistently held more species of big-tree users than
did conifer forests, although the ANOVA showed a significant interaction
of location and forest type (see part A in Table 11.4). Location had no
detectable effect on species diversity of big-tree users. Birds in this guild
were less abundant in northwestern forests and marginally less abundant
in conifer than in broadleaf forests (especially in midwest and south
temperate; refer to part B in Table 11.4).
237
The results for canopy seed predators, indicating a higher frequency of
species and individuals in Chiloe than Alaska (parts A and B, Table
11.2), is at least partly an artifact. Many of the seed predators of the
North American conifer forest are sporadic and even nomadic in occurrence and often do :not breed during the season used by most birds for
nesting (Benkman ; personal communication). Therefore, they are not
often recorded in spring "breeding-bird" censuses and are certainly
underestimated in this study (especially Loxia species).
We compared guild structure of the Chilean bird community to that of
Alaskan coastal forests and that of Canadian interior forests to the east of
the coastal range of mountains near Juneau to determine if the bird
communities of the two rainforests (Alaska coastal, Chiloe) are convergent in structure. The guild structure of Chilote forest birds is no more
similar to that of Alaskan coastal forests than it is to that of Canadian
forests. The proportionate frequency of species in Chiloe is most similar
to Alaskan forests (specifically conifer forests) for three guilds (big-tree
users, understory birds, leaf-gleaners), and most similar to Canadian
forests of the remaining three guilds (covered nesters, aerial feeders,
canopy seed predators), as shown in Table 11.3. This result suggests that
guild structure of the Chilote forest birds is not particularly similar to that
of Alaskan coastal forest birds.
Comparison of Guild Structure in North and South
Temperate Forests
Patterns
Data from our censuses were combined with data extracted from published
studies, and classified by location (northwest North America, midwest
North America , south temperate) and forest type (broadleaf, conifer).
The resulting six categories were subjected to two-way ANOVA , in a
search for general patterns. Because we already know that there is some
heterogeneity within the northwest region (i.e., between Alaskan coastal
and Canadian interior forests) , this exercise serves chiefly to look for
patterns on a continental scale. Where direct comparisons of these results
with those of the preceding section yield different results, that difference
may reflect the difference in scale and perhaps point to interesting exceptions to generalizations .
Broadleaf forests consistently held more species of big-tree users than
did conifer forests, although the ANOVA showed a significant interaction
of location and forest type (see part A in Table 11.4). Location had no
detectable effect on species diversity of big-tree users. Birds in this guild
were less abundant in northwestern forests and marginally less abundant
in conifer than in broadleaf forests (especially in midwest and south
temperate; refer to part B in Table 11.4).