11. Avian Communities in Temperate Rainforests
Methods
229
Census information consists of point-counts near Juneau and Haines ,
Alaska (58°N-59°N) and on Isla Grande de Chiloe (42°S) , Chile ; Counting stations, located along transects in the study sites , were separated by
> 150 m in Alaska (Willson & Comet, unpublished manuscript) and
>100m in Chiloe (Willson , De Santo , Sabag , & Armesto , 1994). The
counts did not include nocturnal birds , shorebirds, or waterbirds. The
data reported here refer to regularly occurring species , meaning those
that were recorded on more than one census day; each site was sampled
at least four times during the breeding season. All counts were made in
1992 (Alaska: May and June ; Chile: November and December), during
the morning hours. Each point-count lasted 8 minutes, and most study
sites had at least eight points. On average, four points were sufficient to
record 85% of the regularly occurring species observed at each site in
both Chile and Alaska, and 98% (range 93%-100%) of such species
were obtained by six points. Diversity of species is defined as species
richness , for our purposes in this chapter, and all abundance data are
relative abundances, in terms of the number of birds/point/day. All
references to " abundance" have to do with the number of birds detected ;
we did not examine possible regional differences in detectability. Documentation of the Chilean censuses is reported in Willson , De Santo,
Sabag , and Armesto (1994), and that of the Alaska censuses is reported
in Willson and Comet (unpublished manuscript).
For purposes of comparisons of diversity and abundances in Alaska and
Chile for this chapter, we use only study sites that occupied at least 50 ha ,
and most were much larger. The floristically diverse , broadleaf Chilean
forests are dominated by Nothofagus ,Drimys, Weinmannia , and myrtaceous trees (Arroyo, Riveros, Penaloza, Cavieres, & Faggi, this volume) .
Picea sitchensis and Tsuga heterophylla dominate the Alaskan coastal
conifer forests , and Populus trichocarpa comprises the canopy of the
Alaskan deciduous forests in which point-counts were done.
We also ask whether the Chilean forest bird communities are notably
similar in structure to those of the Alaskan coastal forest , by comparing
them to the communities in Canadian forests at similar latitudes. For this
purpose, bird censuses in Picea glauca, Pinus contorta, Populus tremuloides, and Salixll'. trichocarpa/Alnus stands in British Columbia and Yukon
are used.
In addition to point-counts , mist-net censuses of understory birds were
conducted in both areas, both in some of the study sites used for pointcounts and in other sites. Mist nets were operated in the same kinds of
forests as the point-counts, with the addition of some stands of Alnus in
Alaska. A total of 380 mist-net hours were spread over three sites in
Chiloe (8 net s/site) . In Alaska, about 680 mist-net hours were accumulated
in two deciduous sites and 635 net-hours in a conifer site near Juneau
Methods
229
Census information consists of point-counts near Juneau and Haines ,
Alaska (58°N-59°N) and on Isla Grande de Chiloe (42°S) , Chile ; Counting stations, located along transects in the study sites , were separated by
> 150 m in Alaska (Willson & Comet, unpublished manuscript) and
>100m in Chiloe (Willson , De Santo , Sabag , & Armesto , 1994). The
counts did not include nocturnal birds , shorebirds, or waterbirds. The
data reported here refer to regularly occurring species , meaning those
that were recorded on more than one census day; each site was sampled
at least four times during the breeding season. All counts were made in
1992 (Alaska: May and June ; Chile: November and December), during
the morning hours. Each point-count lasted 8 minutes, and most study
sites had at least eight points. On average, four points were sufficient to
record 85% of the regularly occurring species observed at each site in
both Chile and Alaska, and 98% (range 93%-100%) of such species
were obtained by six points. Diversity of species is defined as species
richness , for our purposes in this chapter, and all abundance data are
relative abundances, in terms of the number of birds/point/day. All
references to " abundance" have to do with the number of birds detected ;
we did not examine possible regional differences in detectability. Documentation of the Chilean censuses is reported in Willson , De Santo,
Sabag , and Armesto (1994), and that of the Alaska censuses is reported
in Willson and Comet (unpublished manuscript).
For purposes of comparisons of diversity and abundances in Alaska and
Chile for this chapter, we use only study sites that occupied at least 50 ha ,
and most were much larger. The floristically diverse , broadleaf Chilean
forests are dominated by Nothofagus ,Drimys, Weinmannia , and myrtaceous trees (Arroyo, Riveros, Penaloza, Cavieres, & Faggi, this volume) .
Picea sitchensis and Tsuga heterophylla dominate the Alaskan coastal
conifer forests , and Populus trichocarpa comprises the canopy of the
Alaskan deciduous forests in which point-counts were done.
We also ask whether the Chilean forest bird communities are notably
similar in structure to those of the Alaskan coastal forest , by comparing
them to the communities in Canadian forests at similar latitudes. For this
purpose, bird censuses in Picea glauca, Pinus contorta, Populus tremuloides, and Salixll'. trichocarpa/Alnus stands in British Columbia and Yukon
are used.
In addition to point-counts , mist-net censuses of understory birds were
conducted in both areas, both in some of the study sites used for pointcounts and in other sites. Mist nets were operated in the same kinds of
forests as the point-counts, with the addition of some stands of Alnus in
Alaska. A total of 380 mist-net hours were spread over three sites in
Chiloe (8 net s/site) . In Alaska, about 680 mist-net hours were accumulated
in two deciduous sites and 635 net-hours in a conifer site near Juneau