200 cats in Puerto Rico doomed by 20 years of cat-feeding in name of TNR

Fixing 66 cats in 2008 could have fixed the problem.  Feeding stations put three times that many at risk.

            WASHINGTON D.C.––Pending possible further appeals,  U.S. District Judge Randolph D. Moss on May 20,  2026 appears to have ended the Battle of the Cats at the historic El Morro castle in San Juan,  Puerto Rico,  with defeat on all counts for Alley Cat Allies and Save-A-Gato Inc.

The Moss verdict signals probable extermination for many of the estimated 200 cats living along the Paseo that surrounds the El Morro,  and a win for the National Park Service.

(See Why is the Battle of the Cats the longest in the 436-year history of El Morro?)

The National Park Service had since 2005 tried to accommodate concern for the cats despite a 60-year-old park service policy against hosting “invasive species” on park premises.

            Hailed by birders as an affirmation that the trap/neuter/return [TNR] approach to feral cat population control “does not work,”  the Moss verdict is actually an affirmation that feeding feral cats as part of a cat population reduction project is unnecessary,  counter-productive,  and typically creates the very problems it is intended to alleviate.

Alley Cat Allies mis-stated the vacuum effect

Along the way,  Moss addressed at length Alley Cat Allies’ arguments pertaining to the “vacuum effect,”  an ecological phenomenon that Alley Cat Allies’ briefs misrepresented without Moss recognizing the misrepresentation.

The short version of the “vacuum effect” is also often expressed as “Nature abhors a void.”  What it means,  simply put,  is that if a habitat niche exists,  something will fill it.

If a food source exists,  abundant enough to feed more animals than are already consuming it,  more will arrive:  more cats,  rats,  dogs,  crows,  gulls,  or whatever other species the food source attracts.

Diminishing the animal-associated nuisance therefore requires reducing or eliminating the food supply,  not just sterilizing the problematic population of animals already there.

In the Alley Cat Allies version,  preventing the “vacuum effect” requires maintaining a cat population sufficient to keep immigrant cats from converging on the food source.  This is precisely backward when the goal is no cats.

From 120 cats down to 95,  then up to 200

Explained Moss near the beginning of his 89-page decision,  “Plaintiffs are two animal welfare organizations,  Alley Cat Allies Incorporated and Save-A-Gato Inc.

“Save-A-Gato has worked with the National Park Service since 2005,”  Moss wrote,  to administer a neuter/return program,  assisted by Alley Cat Allies,  “which was intended to reduce the free-ranging cat population along the Paseo through sterilization and natural attrition.

“Under that program,”  Moss detailed,  Save-A-Gato “attracted the cats to ‘feeding stations’ placed on the Paseo and then ‘live trapped…spayed or neutered, [and] vaccinated” them before they were “either put up for adoption…or released to the location where they were trapped,'”  according to the Alley Cat Allies summary in legal briefs.

“When Save-A-Gato began administering the TNR program in 2005,”  Moss recounted,  “the cat population at the site was about 120.  Although the population saw an initial dip in the early years of the program,”  down to about 95,  “the National Park Service estimates that the population has since risen to about 200 cats.”

Predictable failure

This was completely predictable if “feeding stations” were part of the project,  maintaining a steady and predictable food supply for cats and other animals,  instead of obliging the resident cats to continue to hunt the rodents who were their primary food source before routine feeding began.

Feral cats,  like any wildlife,  can be baited and trapped.  But easily accessible regular feeding can actually diminish the unique attractiveness of bait,  as a found meal,  and can thereby make a cat less rather than more likely to take the bait and be caught.

How does ANIMALS 24-7 know?

Because we have in fact trapped and had sterilized and vaccinated many dozens of feral cats,  in four states plus Quebec province,  Canada,  in both urban and rural locations,  never using feeding as a component of the project,  repeatedly reducing feral populations to zero without ever having to euthanize cats who were not already terminally ill or injured.

            ANIMALS 24-7 in 1992 included,  and indeed emphasized,  the importance of not feeding feral cats in each of the first three articles describing TNR technique published in nationally distributed media in the United States.

Alley Cat Allies developed constituency of cat-feeders

Earlier,  ANIMALS 24-7 advised the Alley Cat Allies founders,  from experience,  about appropriate ecological considerations and technique.

ANIMALS 24-7 pointed out then,  and in our 1992 articles,  that if cats are present somewhere,  they will,  like any other resident wildlife,  already have adequate food sources;  adding more will only tend to attract more cats,  and change cat behavior from hunting mainly rodents at night to waiting for feedings by day,  hunting birds––who are not around at night––for sport.

            ANIMALS 24-7 did,  however,  encourage TNR practitioners to identify cat-feeders already active in locations with problematic free-roaming cats,  to enlist their help in trapping and counting cats,  as otherwise cat-feeders might release cats from traps and otherwise interfere with an effective sterilization and vaccination program.

Alley Cat Allies unfortunately went on to develop a donor constituency of cat-feeders,  evolving from a focus on cat population reduction to largely engaging in cat-feeding advocacy,  to the detriment of effective TNR as it was designed to be practiced,  as essentially a mechanism for rabies control and humanely transitioning the predator role,  where practicable,  to native species such as coyotes,  foxes,  fishers,  bobcats,  hawks,  owls,  and eagles.

From five feeding stations,  up to eight

Meanwhile back at El Morro,  in San Juan,  Puerto Rico,  Save-A-Gato in 2005 was “allowed to maintain five feeding stations along the Paseo,”  Judge Moss recounted,  “and it agreed to remove 12 cats from the Paseo in the first year,”  and to submit written progress reports to the National Park Service.

“The National Park Service,  in turn,  agreed to ‘allow unlimited access to members of Save-A-Gato for activities related to feeding, trapping,  and population surveys.

“By 2008,”  Moss noted,  “the free-ranging cat population count in the Paseo had declined to 95.”

That 20% cat population reduction should have been followed by at least a 20% reduction in feeding,  if cats were to be fed at all.  Instead,  Save-A-Gato “was permitted to increase the number of feeding stations to eight,”  Moss said.

That appears to have been the mistake that doomed the project:  more food predictably brought more cats.

“At the request of the National Park Service,”  Moss mentioned,  “Save-A-Gato has since removed feeding station #8 at the westernmost point of the Paseo,  leaving seven feeding stations currently.

“Get 70% or flunk”

             “In light of the increase in the Paseo cat population,”  continued Moss,  “the National Park Service concluded that ‘The TNR program on its own is unable to bring the park into compliance with existing authorities for invasive species,  wildlife,  and feeding animals within the park.’

“Specifically,  the National Park Service noted that the cats are an invasive species, and it concluded that ‘TNR is most effective in a closed system’ and with ‘exceptionally high’ sterilization rates.”

While Moss did not describe what these ‘exceptionally high’ sterilization rates are,  the medieval mathematician Leonardo Fibonacci Bonacci of Pisa determined approximately 800 years ago that a population of any species will tend to remain stable so long as 30% are able to reproduce.

The Fibonacci rule turns out to apply equally to species from viruses and bacteria to blue whales and elephants.

In application to vaccination programs,  TNR,  and other species population reduction efforts,  it translates into “Get 70% or flunk.”

(See Pet Overpopulation and the 70% Rule.)

 Alternative Three

If the Paseo cat population was 95 in 2005,  66 cats needed to be sterilized within the first breeding cycle just to achieve stability.

“In a population that is not isolated,  such as the one at [the Paseo] TNR is not effective,”  the National Park Service concluded,  since “New cats come into the colony from other populations and from being abandoned by owners.”

This would not occur without food sources sufficient to attract new cats,  also indicating cat owners that the site might be congenial to abandoned cats.

Eventually the National Park Service,  after a process of public consultation,  selected a different approach identified as Alternative 3.

“Under Alternative 3,”  Moss summarized,  “the National Park Service would publish a request for letters of interest from any animal welfare organization interested in working with the park to perform cat removal.

“The selected animal welfare organization would then trap and remove the cats using the existing feeding stations for a six-month period.  Each month within the six-month period,  a feeding station would be removed until no more feeding stations remain.

“Suitable cats would be placed for adoption or in animal welfare facilities with space.”

Most,  inevitably,  would be euthanized.

TNR with continued feeding would not eradicate feral cats

Argued Moss,  “The National Park Service did not simply reject the use of a TNR program out of hand on the thought that the agency was legally barred from taking that approach.  Rather,  it concluded that the [TNR] approach would not achieve the policy and legal objectives of controlling or eradicating the cat population and that,  under these circumstances, permitting the continued feeding of the cats would violate the agency’s regulations.

“More importantly,”  Moss wrote,  “the National Park Service did,  in fact,  consider ‘suggestions to modify the current conditions,’  such as minimizing or improving feeding stations,  creating cleaning plans,  deploying litter boxes,  installing hand-washing stations,  and limiting cat food output, ”  all of which were “dismissed from further consideration because the National Park Service concluded,”  in view of the cat population increase,  that such alternatives did not further the goal of eliminating the presence of cats.

Cats,  rats,  & iguanas

“As for wildlife and wildlife habitat,”  Moss continued,  “although the National Park Service acknowledged that it ‘has never completed a natural resources assessment,’ it used citizen scientist data to survey the wildlife,  plant life,  and other invasive species at the site,  including rats and iguanas who have been observed eating at the feeding stations.

“The National Park Service concluded” that continuing with the situation as it is ‘would continue to have the same impacts on wildlife and wildlife habitat,  including ‘displacement,  predation,  and potential disease transmission, as well as supplemental feeding of other invasive species (i.e. rats and iguanas) through continued use of the feeding stations’ and “unauthorized feeding where people leave piles of kibble or cans of cat food in the park.”

Note:  iguanas are native,  not “invasive,”  in Puerto Rico.

The National Park Service also came to believe that “removing the feeding stations will discourage animal abandonment” along the Paseo,  describing a phenomenon identified since the earliest days of organized,  monitored TNR programs as “The billboard effect,”  whereby feeding stations are seen by the public as signs saying “Dump cats here.”

“More drastic action was required”

“After attempting to reduce or eliminate the free-ranging cat population,  an invasive species,  on the Paseo using the TNR program,  and after careful study,  the National Park Service concluded that the growing presence of cats detracts from the experience of visitors to a historic site and poses a risk to public health and other wildlife,”  Moss summarized.

“It,  accordingly,  concluded that more drastic action was required.  The Court recognizes that Plaintiffs,  along with many members of the public,  disagree with the agency’s assessment and decision and that,  unlike the National Park Service,  they regard the cats as a valued and non-threatening part of the experience of visiting the Paseo.

“The Court’s sole role,  however,”  Moss finished,  “is to determine whether the National Park Service complied with the National Environmental Policy Act and the Administrative Procedure Act in reaching its decision. Because the National Park Service did so,  Plaintiffs’ lawsuits fail as a matter of law.”

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