Animals have natural biological rhythms and adaptations influencing whether they are active during the day (diurnal), around dawn/dusk (crepuscular) or at night (nocturnal). However, the external environment can be a driving force in altering that natural pattern.
The Puente Hills Preserve is home to a wide range of
crepuscular and nocturnal animals including, but not limited to, the following
animals:
- Crepuscular: cottontail rabbits, mule deer, mice, rattlesnakes, hummingbirds, songbirds, mosquitoes, moths, some beetles
- Nocturnal: foxes, owls, bats, mule deer,
skunks, raccoons, bobcat, coyote, mountain lions, rattlesnakes
Benefits of being crepuscular
There are numerous benefits of being crepuscular. The temperatures around dusk and dawn can be
the most comfortable time of day especially when daytime and nighttime temperatures
can be more extreme. In low light
conditions, animals can blend in better to their surroundings allowing them to
hide while they forage. Being
crepuscular also allows many animals to avoid predators by being active when
predatory animals, such as mountain lions and bobcats, are typically not. But also many species, such as mule deer,
have eyes adapted to see in those light conditions. During this small window of time (currently
approximately 1.5 hours before sunrise and after sunset), crepuscular animals
must feed, find mates, seek shelter, etc. and many species are only active
during the crepuscular and/or nocturnal hours.
General recreational impacts
Some diurnal animals of the Puente Hills Preserve,
such as the California ground squirrel (Spermophilus
beecheyi) and the Western Scrub-Jay (Aphelocoma
californica), may become habituated
to recreationists during the day because of the regular activity going on
around them. However, there are more
people on the trails than before (use at Hellman increased 798% between 2005
[Martino et al. 2006] and 2012 [Garbat et al. 2013]), and when recreation
levels in the Preserve were much lower, there was presumably less recreation
use between sunset and sunrise. Rangers
are now spending increasing amounts of time trying to get recreationists out of
the Preserve at sunset. This increased
level of recreational activity may cause crepuscular and nocturnal wildlife to become
alarmed by human use and modify their behaviors, potentially having deleterious
effects on their survival (e.g. increased heart rate, decreased foraging)
and/or breeding (e.g. nest abandonment).
With increased human use, especially after sunset and before sunrise, concerns
are that these effects on wildlife may become amplified. The type of activity recreationists are
engaging in may also matter since hikers may be more likely to approach
wildlife and travel slower than bikers so they have an increased time of
disturbance in one area. Papouchis et al. (2001) found that hikers caused the
most severe responses in desert bighorn sheep where sheep fled in 61% of the
encounters with hikers as compared to 6% of encounters with bikers. Wildlife may have energetic losses when they
are intentionally or unintentionally harassed and flee from their normal
activities or preferred habitat expending more energy on fleeing/flight in
addition to the potential loss of foraging time. Additionally,
noise may disturb wildlife and it is typically quieter in the Preserve during
the crepuscular and nocturnal hours. In some
studies, noise caused by visitors resulted in increased levels of disturbance
to birds (Bowles 1995; Burger & Gochfeld 1998). In general, the presence of dogs were found
to cause birds to flush (Burger 1986; Pomerantz et al. 1988;) and unleashed
dogs were found to pose a direct threat to birds because they can chase and
kill them (Burger 1986), and they may be especially disruptive off-leash due to
their resemblance to coyotes and foxes (Sime 1999), thus eliciting a predator
avoidance response by wildlife.
Crepuscular/nocturnal use impacts
With such little time for crepuscular animals to
accomplish their daily activities, recreation during this time may interrupt
these activities with potential negative effects on wildlife. With more people on the trails now and
user-created trails bisecting habitat, pressures on wildlife from recreational
activities can cause many diurnal animals to shift their activity times to
being more crepuscular or even nocturnal (George and Crooks 2006). Therefore periods of relief for wildlife,
such as during the crepuscular and nocturnal hours, become increasingly
important. The biggest effect is the
cumulative effect of nighttime disturbance on wildlife that has already been
displaced or disturbed by human activity during the daytime (see general
recreational impacts above).
Additionally, if people are in the Preserve at twilight/night, and using
lights, those lights can impair wildlife’s vision which can disrupt foraging
and young rearing, to name a few (Green and Higginbottom 2001).
Studies on/near the Preserve
Most recently Whittier College senior, Bo Gould, has
been analyzing USGS wildlife camera data (unpublished) for bobcat, coyote, gray
fox, mule deer, raccoon, and striped skunk from 12/30/2012 to 6/30/2013 and
analyzed what percent of the wildlife detections occurred in the daytime versus
the nighttime. These data indicate that
these species may be shifting their activity times at Turnbull Canyon and
Hellman Park into the nighttime compared to the core habitat where they are
active in both the daytime and nighttime.
The cameras at Hellman Park, Turnbull Canyon and the core habitat were
active for 147 days, 170 days and 181 days, respectively which can account for some
of the higher number of detections at Turnbull Canyon and the core habitat.
Several other studies have been conducted on or near the Puente Hills Preserve investigating the effects of recreation on wildlife. A 2002 report by Haas and Turschak stated that coyote and mule deer shifted their activity times to more nocturnal hours after opening the Colima tunnel within the Puente Hills Preserve to human recreation; a pattern which continued during a follow-up study conducted by Lucas (2010) but now also included a nocturnal shift in bobcat activity. This may have negative effects like decreased feeding efficiency, increased predation, and increased energy demands.
In a study conducted on the Nature Reserve of Orange
County (within 40 miles of the Puente Hills Preserve), George and Crooks (2006)
found that in areas with high human activity, bobcats and coyotes were less
active in the daytime and exhibited a lower range of activities. Bobcats were found less frequently along
trails with high recreation use (hikers and bikers) and were more nocturnal,
versus diurnal, in areas with high recreational use (again hikers and bikers)
and when dogs were present. Although coyote activity was also lower in sites
with higher recreation use and coyotes were also temporally displaced by dogs,
they were not as sensitive to human disturbance as bobcats. In short, the study by George and Crooks
illustrates that recreation use can alter wildlife behavior. These are important findings since our
Preserve has both hikers and bikers, allows dogs in more areas than not, and
bobcats and coyotes are present on the Preserve and as top predators are good
indicators of ecosystem health.
Conclusion
With the continual added pressure due to increased
human activity during the day, it becomes more important to provide relief to
wildlife during crepuscular and nocturnal times. In addition, other challenges to the Preserve are limited Ranger resources to control
human activities and close all trailheads at sunset as well as porous access
points when the Preserve is closed.
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