Point Count Bird Censusing Data Subset for Paper 'EFFECTS OF LAND USE AND VEGETATION COVER ON BIRD COMMUNITIES' Walker et. al

Animals utilize their environment across a range of scales, which is
bounded by their extent, the broadest spatial area which organisms respond to
their environment within their lifetime, and the spatial grain, the smallest
area they respond to their environment (Kotlier and Wiens 1990). Within this
range, organisms likely respond to their environment at a hierarchy of levels.
Johnson (1980) recognizes four distinct levels of hierarchical habitat
selection. At the very largest scale, first order selection, includes the entire
area that an organism utilizes within its lifetime, and is also known as an
organisms global home range or extent. In contrast, second order selection is an
organisms local home range, or the area that it occupies within a unique
ecosystem. This distinction is most apparent with migratory animals who utilize
more than one distinct landscape for their survival (i.e. summer vs. winter
feeding grounds), and much less so for organisms resident of one specific
landscape for their entire life span. Third order selection is the selection of
specific habitat patches within an ecosystem. For example, a Monarch butterfly
would tend to select patches of milkweed within a prairie. And the lowest level,
fourth order selection, involves the physical procurement of food within a
selected patch, in our example, specific flowers within a milkweed patch, and is
also known as grain. Realizing the importance of hierarchical habitat selection,
it has become apparent that single-scale studies of animals responses to their
environment may fail to adequately represent how that specific animal is
responding to ecological parameter of interest, especially if they are not
responding to the landscape at that scale (Holling 1992). The range of scales
which an animal of interest is utilizing a landscape is important to determine
prior to any further ecological investigation, as inappropriate scalar mismatch
between organism and environment can lead to ambiguous or even deceptive
conclusions. To do this, we compared the correlation coefficients of bird
abundances for different functional groups (e.g. foraging guilds, natives vs.
exotics) with vegetation cover, as a proxy for habitat, across a range of scales
(from 100m to 10km). Theoretically, a unimodal (hump-shaped) relationship should
exist for the correlation coefficients across a range of scales, under the
assumption that vegetation cover is an adequate estimate of bird abundance. The
peak of that relationship, if statistically significant, would represent the
strongest correlation between habitat and bird abundance, and thus signifies the
average third order selection unit for that group. A strong peak is expected for
species directly dependent on vegetation for food (herbivores), a weaker peak
for omnivores, and the weakest relationship for those species indirectly
dependent on vegetation (insectivores). The regional distributional patterns of
the varying bird functional groups was also estimated by utilizing interpolation
techniques designed for avian censuses in urban systems. Exotic species were
expected to be spatially aligned to the urban ecosystem, and native species tied
to the desert ecosystem. Herbivores were expected to exist in higher densities
were vegetation is greatest, which typically exists within the city and
agricultural fields in arid ecosystems. The ongoing project (since October 2000) is documenting the abundance and
distribution of birds in four habitats (51 sites): Urban (18) Desert (15) Riparian
(11) and agricultural (7). The 40 non-riparian sites are a subset of the 200 CAP-
LTER points. We are using point counts to survey birds four times a year (January,
April, July and October). During each session each point is visited by three birders
who count all birds seen or heard for 15 minutes. Our goal is to study how different
land-use forms affect bird abundance, distribution and diversity in the greater
Phoenix area in order to predict and preserve high bird species diversity as urban
development is proceeding. We have now just completed 3 years of monitoring, and are
also beginning to see some of the sites changing due to new urban development. The
results described below are based on analyses of the first two years data.