Wildlife and Anthropogenic Changes in the Arid Southwest - Design with the Desert: Conservation and Sustainable Development - page 171

rely on saguaro and other cacti to meet habitat requirements, and development typically
eliminates habitat for these species. 13,14 Small mammal communities also change with
urbanization. Although suburban neighborhoods with low housing density (0.2 houses/ac)
maintained the native nocturnal rodent community found in undeveloped areas, medium
density housing (3 houses/ac) did not and in fact encouraged colonization of an exotic
species, the house mouse. 15 Lesser long-nosed bats will readily use hummingbird feeders
as a food replacement for cactus flowers but these bats apparently do not tolerate artificial
lights so remain at the edge of developed areas around Tucson. 16 Some bats use swimming
pools as water sources, and Mexican free-tailed bats roost under bridges and forage on
insects drawn to artificial lights. These examples highlight the variation among organisms
as to whether habitat is best viewed as “altered” or “lost” following development.
Although many wildlife species effectively lose habitat following urbanization,
those that respond to the perturbation as habitat alteration experience both pluses and
minuses. Cooper's hawk's nest in urban Tucson, selecting native fremont cottonwood
( Populus fremontii ) or non-native eucalyptus ( Eucalyptus spp.) and aleppo pine ( Pinus
halepensis ) for nests. Neither level of disturbance at nest sites nor percent cover of buildings
around a nest was a factor in selection. 17-19 Density of nests was higher in the city relative to
exurban (outside the city) areas. However, mortality was higher for nestlings in urban areas
compared to exurban areas, and the likely cause of death was trichomoniasis caused by a
parasitic protozoan. Bird feeders can promote spread of this disease (especially through
common species such as doves), and bird feeding is common in urban and suburban areas.
Other causes of mortality for urban Cooper's hawks were collisions (e.g., with windows)
and organophosphate poisoning used to rid neighborhoods of feral pigeons.
9.4 Habitat Fragmentation
Division of contiguous habitat by roads, railroads, canals, dams, and other barriers has
affected the population biology of many vertebrates. One of the most dramatic new barriers
in the Southwest is a 660 mile long border wall being constructed along the United States
and Mexico border. 20 This wall hinders movement of wildlife such as javelina and deer,
including some endangered species such as the jaguar (Figure 9.4). Fragmentation affects
wildlife movement both among and within habitat patches and can influence genetic struc-
ture of populations.* The behavior of even relatively mobile animals, such as mammals and
birds, can be altered because of subdivided landscapes resulting from urban development. 23
Roadways not only represent barriers to movement, especially of smaller wildlife species
such as amphibians and reptiles, but also represent a significant source of mortality. 24
Desert mule deer near Tucson, Arizona, primarily selected habitat based on forage qual-
ity, slope, and elevation; however, during parts of the year, deer avoided roads, rivers, and
canals. 25 For this species, as urbanization increases road density, and habitat becomes more
fragmented. Designating wildlife corridors may help mitigate this problem. Although less
than 25% of desert mule deer sightings were in a designated corridor for wildlife and
remaining locations were in undeveloped lands, some of these lands are scheduled for
agricultural development. Deers are likely to increase their use of the designated wildlife
corridor if this development occurs. 26
* See reviews in Kwiatkowski et al. 21 and Dixo et al. 22