Hello Linda:
You have misrepresented a very complicated mathematical model when you
concluded that our research "shows TNR programs have no impact on feral cat
populations." This was not the published conclusion of the paper.
The goals of TNR are multifaceted and include:
1) prevention of the birth of feral kittens (75% of which may not survive to
adulthood)
2) improvement of the welfare of the cats that live in managed colonies
3) reduction of the size of targeted colonies
4) reduction of cat populations in targeted neighborhoods
5) reduction of cat populations in larger regions
Our group and other scientists have published numerous papers in scientific
journals that have proven the success of TNR in accomplishing goals 1-4;
some of these are referenced in the current paper if you are not familiar
with them. These are well-documented significant impacts of TNR on feral cat
populations.
Not surprisingly, the new model did not predict that the scale and duration
of the two TNR programs in the study would produce a statistically
detectable impact at the larger county-wide level. You incorrectly state
that "From 1992 to 2003, 14,452 cats were trapped, neutered, and released
out of an estimated 240,690 feral cats in San Diego County, CA. From 1998
to 2004, 11,822 cats were trapped, neutered, and released out of an
estimated 36,398 feral cats in Alachua County, FL." The number of cats
trapped is the accumulated total over the years whereas the estimated
population sizes are approximately the same each year (but not necessarily
the same cats). Thus, it is improper to suggest that 6-32% of the total
population was trapped as you state. In reality, only 0.5-6% of the total
county cat population was trapped each year. This may seem like a small
point, but it is critical to avoid misuse of the model. The model predicts
that increasing the trapping percentage to 14-19% annually would
successfully reduce cat population growth. Thus, TNR is not a failed
concept, it simply needs to be practiced on a larger scale.
It is not uncommon for lay persons to have difficulty understanding the
concept of models. Models are mathematical predictions of what might happen
when certain conditions exist in the environment. Models provide a starting
point for developing programs and public policy. However models are not the
same as an actual study of the program or policy outcome. Perhaps one of the
most graphic example of models gone wrong occurred in the presidential
election in Florida. Even though the models were built by experienced
analysts using up-to-the-minute data, they predicted the wrong outcome of
the election. Similarly, a recently published model on feral cat control
(Anderson MC, et al, JAVMA 2004) predicted that unmanaged cat populations
would increase exponentially. This would be a population growth pattern that
is virtually unheard of in any mammalian species. Since most feral cat
populations remain unmanaged, the Anderson model would predict that we would
literally be knee-deep or worse in cats, which is clearly not the case.
All this means that models provide a great starting place for addnaged, the
Anderson model would predict that we would literally be knee-deep or worse
in cats, which is clearly not the case.
All this means that models provide a great starting place for addressing
problems, but they should be replaced as quickly as possible with real
studies that test the actual (instead of theoretical) outcomes of control
programs.
BTW, have you seen the recently published model which predicts that reducing
cat populations would actually cause more harm to birds due to a resulting
increase in rat populations (Fan M, et al, Bull Math Biol, 2005)?
Interesting!
Mark Twain said, "Get your facts first, then you can distort them as you
please." While this may be a strategy in the war against feral cats, I hope
that you will not intentionally distort the growing body of scientific
literature that we desperately need to make informed decisions about
managing feral cats.
Julie Levy, DVM, PhD, ACVIM