Bobcat Population Study
Iowa Department of Natural Resources
Iowa State University
Conservation of Large Carnivores
Restoring large carnivores is one of the most
challenging ecological and sociological problems facing
wildlife managers today. Despite previous population
reductions and large-scale habitat loss, carnivores are making a
surprising recovery throughout North America. Restoration of
large carnivores has become a great interest to the general public, hunters, and trappers. The
Iowa Department of Natural Resources (DNR) is now specifically interested in the recovery of
bobcats (Lynx rufus). In Iowa, reports of bobcats in the last 5 years have become increasingly
common in about two-thirds of the counties, although it is still generally thought that bobcats are
sparsely distributed. In 2003, the Iowa DNR, in cooperation with Iowa State University, initiated
a study on the status and ecology of bobcats in Iowa so that population expansion could be
documented and conservation options could be defined.
Basic Ecology and Habitat Use
Bobcats are medium-sized carnivores (15-26 lbs) with home range areas that vary widely
depending on the region and habitat. In the bottomland forests of Mississippi bobcats range over
only about 2 miles2 whereas in the plains of Montana they cover 20 miles2. Bobcats generally
select forest or brushy areas where there is abundant small mammal prey (rabbits, squirrels, and
mice). Bobcats are nocturnal animals with activity peaks around sunrise and sunset and hunt
alone, by means of stalking and ambushing prey. Bobcats do eat livestock, especially sheep and
chickens, although the impact is generally minor. Birds typically comprise less than 10% of their
diet. Female bobcats older than one year will become pregnant once per year with a single litter
of 3 to 4 kittens. Den sites of bobcats are moved by the females several times during the rearing
period and consist of rock shelters or dense piles of brush. During the breeding season males
travel widely and may breed with more than one female. Kittens and yearlings are particularly
vulnerable to mortality and perhaps only 30% will live to their 2nd birthday. Adults may live to
age 3-5, although animals as old as 10 years may be found.
Project Objectives and Anticipated Benefits
The goals of this project include determining the distribution, habitat relationships, and
population ecology of bobcats in Iowa. Our specific objectives are to: 1) Solidify data about the
distribution of suitable habitat and the presence of bobcats in Iowa; 2) Determine local habitat
selection by bobcats, including home range characteristics and dispersal patterns in relation to
the landscape; 3) Evaluate population monitoring techniques that can be reliably and efficiently
used to survey bobcats in Iowa; 4) Determine recruitment and survival rates of bobcats in Iowa;
5) Evaluate genetic similarity of the Iowa population in relation to populations in other states.
An important objective of our research is to determine how relatively small patches of
forest and grassland distributed in the agricultural landscape of Iowa will influence habitat
selection and population persistence of bobcats. Roadways, vehicular traffic, and other human
activity could negatively affect bobcat populations through mortality and avoidance. Local and
statewide habitat maps can be linked to population data to anticipate the effects of habitat
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changes. The project will provide wildlife biologists the foundation to conserve and manage
bobcat populations in Iowa, including changes in protection status and conservation regulations.
Bobcat Distributions
Initially, reports of sightings and road kills provided important information on bobcat
distribution. For example, we distributed a bobcat sighting postcard to DNR personnel and at
meetings with the general public. To document statewide distribution more systematically we
initiated a bow hunter observation survey. Through the bow hunter survey we can estimate the
presence of bobcats at both the county and climate region level. As the survey is repeated over
the years, we will be able to reliably detect regional differences in sighting of bobcats. From the
2004 bow season we can clearly see that bobcats are most abundant in the southwestern and
southern part of Iowa (Figure 1). Read the complete report at:
http://www.iowadnr.com/wildlife/pdfs/bowobserver_survey2004.pdf
Figure 1. Bobcat sightings (red dots) and carcasses (blue dots) and their relative locations
across the state of Iowa.
Dispersal and Habitat Selection
The low density and secretive nature of bobcats makes it difficult to monitor population
levels and to determine habitat selection. Bobcats are curious, just like house cats, making them
relatively vulnerable to trapping. To monitor bobcat behavior we have radio-collared bobcats
throughout an 8-county region in south-central Iowa (Warren, Marion, Clarke, Lucas, Monroe,
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Decatur, Wayne, and Appanoose
counties), encompassing about 4400
miles2. Trappers and landowners have
contributed essential effort to our study
by contacting us when a bobcat has been
accidentally caught in a trap. Our
research crew immediately heads for the
scene so they can anesthetize the bobcat,
attach a radio-collar, sex, weigh, and
roughly classify age based on size and
tooth wear. We also collect tissue
samples for genetic and disease analyses, and extract a tooth to determine the exact age of the
collard bobcat. Bobcats are then tracked using a combination of vehicle-mounted antennas and
satellite transmitters. We locate each animal at least 2 times/week and sometimes intensively
track individuals throughout the night to estimate habitat use and movement patterns.
Between 2003 and 2005 we have radio-collared and tracked 44 bobcats. Not surprisingly
we found evidence for selection of forest habitat, especially during the winter, and significant
avoidance of rowcrops during summer and winter. Home-range estimates for males were 42
miles2 in the summer and 33 miles2 in the winter (Figure 2). Adult male home-ranges in this
study were larger than previously reported in adjacent states (Kansas, Illinios, and Wisconsin).
The larger home-ranges are likely due to low population densities (males have to travel farther to
find females), and habitat fragmentation (bobcats have to travel farther to find suitable habitat
patches). Female home-ranges were smaller than males in area: 9 miles2 during summer when
females are with kittens and increase in to an average of 14 miles2 in the winter when food
resources are more scarce. Our radio-collared animals have survived very well; survival of
males has been 87% annually while that of females has been 84%.
Figure 2. Bobcat winter (left) and summer (right) home-ranges for male bobcats (blue
outline) and female bobcats (red outline) in south-central Iowa.
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Recruitment and Survival
Since 2001, we have recovered and examined 280 bobcats carcasses from 31 counties in
Iowa (Figure 1). We could accurately determine the cause of mortality of 142 carcasses which
were classified as: 69% incidentally trapped, 29% automobile kills, and 2% illegally shot. Sixty
percent of the carcasses were classified as adults at least 2 years old and the oldest bobcat we
have collected was 9 years old. Younger animals are often underrepresented in carcass
collections. By examining the reproductive tracts, we could tell that about 80% of the females 2
years old or older had bred during the past year but it is not yet clear whether yearling females
typically become pregnant. Litters averaged slightly more than 3 kittens per litter. From the
recruitment and survival data we can calculate that the population in southern Iowa is growing at
about 7% per year. We continue to analyze the radio-telemetry and genetic data so that we can
predict how bobcats will disperse across Iowa.
Conclusions
When we began this project we were unsure whether we would successfully find and
mark many bobcats in Iowa. But through the collaborative efforts of trappers, landowners,
interested citizens, DNR technicians and biologists, and Iowa State University researchers we
have created a successful project. The project is supported by the State Wildlife Grants program
that uses federal funds, which are matched with those of the DNR, and the university to support
the effort. We have collected much data since 2003 and we expect to complete the first phase of
reporting during 2006. We plan to continue to trap, collar, and track bobcats in south-central
Iowa beyond that time. The interest by the public and the continued cooperation of trappers and
landowners is essential to success. Before long we should have substantial information upon
which to base conservation and management of this wildlife species.
Contact information:
Dr. William Clark
Professor – Iowa State University
Ph. (515) 294-5176
[email protected]
Dr. Todd Gosselink
Wildlife Research Biologist – Iowa DNR
Ph. (641) 774-2958
[email protected]
Bobcat Project Webpage: http://www.eeob.iastate.edu/faculty/ClarkW/html/bobcat.html