PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

Bird Studies
The forest birds were sampled both summer
and winter on a 6 .0-ha plot chosen t o
represent the Thompson site . This plot was
divided into fifteen 0 .4-ha sample units on a
map of the whole plot . A series of transect s
was made through the whole plot on each
sample day by Erickson who noted each bird
observation by location and species . Durin g
the summer sample period (May and June) ,
many breeding males were singing, whic h
facilitated their detection . During the winter
observation period (December), there had t o
be more dependence on sight than sound .
Five days of observation were spent at eac h
season, and all observations took place during
mornings when there was no heavy rain. Th e
results for the two seasons are given in table
6 .
Some less common, but in some case s
rather large birds, are also found on th e
Thompson site . During the coming year we
will be able to make population estimates of
these species, adding substantially to our total
estimate of bird biomass .
The contrast between summer and winte r
populations is much sharper for birds than fo r
small mammals . This has implications for ecosystem
modeling, since some birds reproduc e
on the Thompson site but winter elsewhere ,
presumably suffering some mortality, an d
thus constituting a one-way movement o f
energy and nutrients out of the Thompso n
site . From a knowledge of body weights w e
have calculated the biomass of common bird s
on the Thompson site by season (table 6) .
Energy-flow estimates for these bird populations
cannot yet be made because neithe r
population estimates of the larger birds no r
annual cycles of abundance of each bird species
are yet available for the Thompson site .
This must be one of our next topics of study .
The role and foraging stratum of birds is
roughly categorized in table 7. As in the case
of small mammals, some of these birds shif t
seasonally in their consumer-roles . A diet of
invertebrates is essential for the young of al l
species. Also, shifts in the relative abundanc e
of available food will presumably be reflecte d
in food habits . These are also topics on which
more work must be done .
Table 6.-Abundance (number per 100 hectares) and biomass (grams per hectare)
of the most common birds by species and seaso n
Species
Abundance
Biom as s
Summer Winter Summer Winter
Molothrus ater 26 0 11 .4 0
Junco oreganus 43 0 9.9 0
Troglodytes troglodytes 36 33 3.5 3 . 1
Hylocichla ustulata 16 0 5.8 0
Dendroica nigrescens 43 0 4.5 0
Parus rufescens 23 0 2.3 0
Regulus satrapa 0 33 0 2 . 0
Oporornis tolmiei 26 0 1 .6 0
Total 213 66 39.0 5 .1
204