11. Avian Communities in Temperate Rainforests
243
Alaskan deciduous forests, intermediate for Chiloe, and lowest for
Alaskan coniferous forests . However, the average number of individual
birds censused was markedly higher at each census point in Chilean
forests, as suggested by Jaksic and Feinsinger (1991), and lowest for
Alaskan coniferous forest . The forests of Chiloe, therefore, support an
avifauna within the range of diversity of Alaskan coastal forests but
substantially denser.
Covered nests are much better represented in the Chilean forest
avifauna than in Alaska or the rest of North America. This difference is
not apparently associated with adaptation to microclimate or probable
risk of nest destruction by vertebrates (although measurements of rates of
nest failure are needed to examine this more closely). Instead, there
seems to be a taxonomic association: Psittacids, furnariids, and rhinocryptids typically nest in holes or build dome nests and constitute a notable
proportion of the Chilean avifauna. Other covered-nesters occur in both
regions: Troglodytids and Tachycineta always use covered nests, and one
species of each occurs in the censused forests of each region. Picidae
always nest in cavities, and occur in both regions, but are not common.
However, a taxonomic association begs the questions of the origin of the
habit. In addition, one reviewer suggested the possibility that long-distance
migrants lack time to build covered nests, but the only Neotropical
migrant in the Chiloe forests is Elaenia albiceps, which builds an open
nest.
The frequency of covered-nesting species on Chiloe contrasts also with
that of New Zealand, where the forest trees have many taxonomic similarities, the climate is similarly wet, and the latitude is comparable, but
the phylogenetic history of many indigenous bird species is very different
from that of Chile. About 20% to 25% of the native species of Nothofagus
forest sites in New Zealand use covered nests (census data from Kikkawa ,
1966; nest information from Anonymous, 1985; Falla, Sibson, & Turbott,
1981). The contrast between the frequency of covered-nesters in New
Zealand and Chile seems to reinforce a taxonomic interpretation of the
high frequency of covered-nesters in Chilean forest birds. However, a
taxonomic correlation in Chile does not provide an explanation that is
generalizable to New Zealand, because there is within-family variation in
nest type for New Zealand birds (Anonymous, 1985; Falla, Sibson, &
Turbott, 1981).
Ecological correlates of small clutches in the northern hemisphere may
include high risk of nest predation, low adult survival, or the existence of
multiple breeding opportunities during the season (Bennett & Harvey,
1988; Martin, 1993a, 1993b, 1995; Martin & Li , 1992; Saether, 1988).
However, such correlations often seem to break down when comparing
temperate and tropical regions (Karr, Nichols , Klimkiewicz, & Brawn,
1990), and preliminary evidence from Chile also suggest that at least
some of these correlations may not hold there . Similarly, most nat ive
passerines in New Zealand produce small clutches (fewer than four eggs),
243
Alaskan deciduous forests, intermediate for Chiloe, and lowest for
Alaskan coniferous forests . However, the average number of individual
birds censused was markedly higher at each census point in Chilean
forests, as suggested by Jaksic and Feinsinger (1991), and lowest for
Alaskan coniferous forest . The forests of Chiloe, therefore, support an
avifauna within the range of diversity of Alaskan coastal forests but
substantially denser.
Covered nests are much better represented in the Chilean forest
avifauna than in Alaska or the rest of North America. This difference is
not apparently associated with adaptation to microclimate or probable
risk of nest destruction by vertebrates (although measurements of rates of
nest failure are needed to examine this more closely). Instead, there
seems to be a taxonomic association: Psittacids, furnariids, and rhinocryptids typically nest in holes or build dome nests and constitute a notable
proportion of the Chilean avifauna. Other covered-nesters occur in both
regions: Troglodytids and Tachycineta always use covered nests, and one
species of each occurs in the censused forests of each region. Picidae
always nest in cavities, and occur in both regions, but are not common.
However, a taxonomic association begs the questions of the origin of the
habit. In addition, one reviewer suggested the possibility that long-distance
migrants lack time to build covered nests, but the only Neotropical
migrant in the Chiloe forests is Elaenia albiceps, which builds an open
nest.
The frequency of covered-nesting species on Chiloe contrasts also with
that of New Zealand, where the forest trees have many taxonomic similarities, the climate is similarly wet, and the latitude is comparable, but
the phylogenetic history of many indigenous bird species is very different
from that of Chile. About 20% to 25% of the native species of Nothofagus
forest sites in New Zealand use covered nests (census data from Kikkawa ,
1966; nest information from Anonymous, 1985; Falla, Sibson, & Turbott,
1981). The contrast between the frequency of covered-nesters in New
Zealand and Chile seems to reinforce a taxonomic interpretation of the
high frequency of covered-nesters in Chilean forest birds. However, a
taxonomic correlation in Chile does not provide an explanation that is
generalizable to New Zealand, because there is within-family variation in
nest type for New Zealand birds (Anonymous, 1985; Falla, Sibson, &
Turbott, 1981).
Ecological correlates of small clutches in the northern hemisphere may
include high risk of nest predation, low adult survival, or the existence of
multiple breeding opportunities during the season (Bennett & Harvey,
1988; Martin, 1993a, 1993b, 1995; Martin & Li , 1992; Saether, 1988).
However, such correlations often seem to break down when comparing
temperate and tropical regions (Karr, Nichols , Klimkiewicz, & Brawn,
1990), and preliminary evidence from Chile also suggest that at least
some of these correlations may not hold there . Similarly, most nat ive
passerines in New Zealand produce small clutches (fewer than four eggs),