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It's Catbirds vs. Cats--and the Cats Are Winning

Ed. note: Below is an article and a response to the article. Both articles have clear agendas and the truth lies somewhere between them. The fact is that most cat owners don't believe that THEIR cat kills any wild birds or mice, and that letting them outside is in the cat's best interest. This information should be used to educate cat owners about the deaths for which they are responsible. On the other hand, feral cats, like all wild animals, are in a separate category with regard to animal rights ethics. Feral cats need to kill to live. Domestic cats kill for entertainment. Killing to survive is moral. Killing for entertainment is not.

By Tina Gheen

gray bird perched on stick

Scientists from the Smithsonian Migratory Bird Center and Towson University began a study to determine how well birds are surviving in suburban areas. Specifically, they wanted to determine the success of gray catbirds (Dumetella carolinesis) in areas with concentrated populations of people. They looked at nest success, the probability the baby birds will survive through incubation and as hatchlings, and post-fledgling survival rates, the period after the birds leave the nest, but before they migrate.

From May to September, with the help of ordinary citizens participating in the Smithsonian's Neighborhood Nestwatch program, the team studied catbird nests in 3 suburban neighborhoods in Maryland: Spring Park, Opal Daniels Park, and Bethesda.

adult catbird with green caterpillar in its beak at nest with nestlings

Catbirds typically build large, recognizable nests in the middle of dense shrubs or trees, so they were fairly easy to locate. The nests were monitored every 2 to 4 days both during incubation, which lasts about 12 days, and the nestling stage, which lasts about 11 days, until the nests either failed or the baby birds fledged.

The chicks were banded and weighed, and some of the nestlings and juvenile catbirds were fitted with tiny radio transmitters. These transmitters allowed the researchers to locate and track the birds after they began to fly. It also allowed them to locate the transmitter after a bird had died.

This gave the researchers important insights as to how the birds died and revealed tell-tale clues about any predators involved. For example if the transmitter was found underground, the bird was most likely taken by a rat in the suburban environment.

Sadly, predators were responsible for 79 percent of the mortalities of the juvenile catbirds in the study. Of those deaths, nearly half were attributed to cats in Opal Daniels Park and Spring Park. Predation was highest the first week after the birds had fledged.

Since the baby birds are noisy and constantly receiving attention from the parents during that first week, domestic cats are most likely intensely monitoring and hunting the inexperienced birds during this time.

Most scientific studies attribute predation to native animals such as hawks, snakes, and chipmunks, but the D.C. study found that novel, or new, predators such as cats may be driving the survival rates of juvenile birds in suburban areas instead.

Since domestic cats can thrive in large numbers in suburban environments because they aren't under the usual environmental pressures of limited food resources, disease, and competition for survival, they are in a position to dramatically influence the success of bird populations.

After examining the results from each neighborhood, the scientists discovered something else. The results showed that habitat suitability for the catbirds varied from neighborhood to neighborhood in the suburban environments. The birds in the Bethesda neighborhood were much more successful than catbirds in the other 2 neighborhoods.

In particular, the nestlings in Bethesda had a very high survival rate. The study showed that although each neighborhood site provided the right kind of habitat, predators, especially cats, often tipped the balance against the young birds' survival.

This article summarizes the information in this publication:

Balogh, Anne L., Ryder, Thomas B., and Marra, Peter P. 2011. Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats. Journal of Ornithology.

Understanding factors that limit the productivity and survival of birds in rapidly changing human-dominated landscapes are key to managing future population persistence. To date, few studies have quantified both nest success and post-fledging survival for birds breeding within the suburban matrix. Here, we estimated nest success and juvenile post-fledging survival for Gray Catbirds (Dumatella carolinensis) and used those site-specific parameters to model source--sink dynamics at three sites in suburban Washington DC (USA). Cumulative nest success probability varied substantially among suburban sites and indicated that in some cases suburban habitats may provide suitable breeding sites for passerine birds. In addition, we documented the effects of sex and brood size on postfledging survival rates and determined the role of predation on dispersing fledglings. Like nest success, estimates of post-fledging juvenile survival also varied among sites and highlight the importance of site-specific demographic estimates in urban habitats. Predation accounted for 79% of all mortalities, with 47% of known predation events attributable to domestic cats (Felis catus). Our models of source--sink dynamics underscore the importance of seasonal recruitment parameters for calculating population growth rate and subsequent persistence. This study provides parameter estimates for two critical life history stages in the avian annual cycle in the suburban matrix and posits that predation drives differential nest and postfledging survival within human-dominated environments.

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Breaking Down the Bogus Smithsonian Catbird Study

As advocates for all animals, we were dismayed by the irresponsible and biased conclusions of a 2011 study on bird deaths from the Smithsonian Institution.

'Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats,' published in the Journal of Ornithology1, is a limited study that cannot be extrapolated to represent the complex cat-bird dynamic nationwide. Much more disturbing, however, is how this data has been manipulated to malign cats and used widely to dredge up a false and counterproductive debate.

The Smithsonian's Conclusions Exaggerate the Facts

The Smithsonian study relies on an extremely small sample size (just 69 birds) in a very limited radius (three sites within mere miles of each other). Opponents of Trap-Neuter-Return have already latched onto this study to clamor for cats indoors--a concept that, it is worth noting, is a death sentence for countless feral cats--but they are mishandling the data and misleading the public.

It is absurd to think that a minor study conducted on a single species of bird in a small area of suburban Maryland could accurately be used to characterize the relationship between cats and birds in landscapes all over America.

The press release circulated by the Smithsonian's National Zoo further exaggerates and misconstrues the study's findings, dramatically painting cats as the major threat to birds by stating that of the birds studied 'almost half of the deaths were connected to domestic cats'--specifically, 47%. However, a quick look at the numbers shows this figure to be greatly manipulated:

    Of the 69 birds studied, 42 died during the study. Only six of those deaths can be directly attributed to cats through observation.

    The authors guessed that another three bird deaths could be attributed to cats based on circumstantial evidence.

    The authors inflate the figure to 47% by focusing the discussion only on the number of birds that died due to predators, not the total number of birds in the study. They ignore the 27 birds that did not die, as well as the nine birds that died due to causes other than predation, and the 14 birds that died due to unknown predators. This leaves 19 birds that were killed by known predators.

    The number of deaths attributable to cats is 9 birds out of 69--or 13%--not 47%.

    But when taken as a percentage of all of the deaths from known predators, (9 out of 19) the number of birds killed by cats inflates to 47%--hyping cats-- impact on bird populations way out of proportion.

Statistics are a powerful persuasive tool because people often take them at face value, but numbers can be manipulated too. The omission of 50 birds--well more than half the sample size--in calculating this figure dramatically changes the conclusions of the study.

As the researchers themselves note, they also failed to examine whether the few deaths attributed to cats were additive--more birds dying than normal--or compensatory--consistent with the normal mortality rate for this species. Considering data from the North American Breeding Bird Survey, which shows the Maryland catbird population to be on the rise, the former seems unlikely. Cats specialize in hunting rodents; also, studies have confirmed that the birds who are caught are generally weaker animals who are not likely to have survived.

Humans are the True Threat to Birds

When rationally viewed, the Smithsonian study and the resulting press flurry has added nothing to the overall conversation about how to protect animals. Instead, it has only drawn attention away from the real threat to birds--people.

Alley Cat Allies wants what's in the best interest of all animals, including birds. Environmental experts say we must change the way we are impacting our environment. Until we can stop going in circles, perpetuating this false debate, and focus on the real threat, we are truly just chasing our tails.

[1] Balogh, Anne L., Thomas B. Ryder and Peter P. Marra. Population demography of Gray Catbirds in the suburban matrix: sources, sinks and domestic cats. Journal of Ornithology. 2011.;

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