Vascular Plant and Vertebrate Inventory of Saguaro ... - USGS

Cumulative number of species
200
180
160
140
120
100
80
60
0 10 20 30 40 50
Sample period
Figure 5.4. Species accumulation curve for all survey methods for birds, Saguaro National
Park, Rincon Mountain District, 2001 and 2002. Each sample period is a randomized
combination of approximately 250 observations.
that consistently predict occurrence of bird
species include vertical structure (MacArthur
and MacArthur 1961, Cody 1981), horizontal
patchiness (heterogeneity; Roth 1976, Kotliar
and Weins 1990), and floristics (Rice et al. 1984,
Strong and Bock 1990). To even the most casual
observer, there are extreme changes in all of the
characteristics from the valley floor to the highest
points of the Rincon Mountains. This pattern
of vegetation change across altitude and aspect
is typical of the “sky island” mountain ranges
of southern Arizona and adjacent Mexico (e.g.,
Whittaker and Niering 1965).
Although the district contains a number
of biotic communities that are characteristic
of the sky island mountains, it shares one of
the biogeographic traits with the herpetofauna
community: it is not as species rich as the sky
island ranges to the south. In particular, ranges
in the U.S., such as the Chiricahua (Taylor 1997)
and Huachuca mountains regularly host breeding
species that have strictly Madrean distributions
including the Lucifer (Calothorax lucifer),
Berylline (Amazilia beryllina), and violet-
63
crowned (Amazilia violiceps) hummingbirds,
eared trogon (Euptilotis neoxenus), Mexican
chickadee (Poecile sclateri), and flame-colored
tanager (Piranga bidentata), to name a few.
Although it likely that some of these species
(e.g., blue-throated hummingbird [Lampornis
clemenciae]) occasionally appear in the Rincon
Mountains (see Inventory Completeness), our
surveys provide further evidence that these
species do not regularly occur there. Two species
that reach their northern breeding distribution
in the district (or nearby mountain ranges) are
the buff-breasted flycatcher and sulphur-bellied
flycatcher. We found the first confirmation of
breeding for the sulphur-bellied flycatcher in
the district, and the buff-breasted flycatcher
may breed there occasionally. A third Madrean
species, the elegant trogon, may also occasionally
breed in the Rincon Mountains, but there has
been no confirmation of this.
An important resource for birds in the
district is the riparian corridor along Rincon
Creek, which had higher species richness than
any other area in the district (Appendix G).