Street dog & feral cat population modeling: catch & kill vs. TNR
From ANIMAL PEOPLE, October 2013: (Actually published on November 20, 2013.)
Nathalie Klinge offered the 2013 International Companion Animal Welfare Conference a model of street dog population management based on real-life experience in Romania that paralleled a model I have used for about 15 years to project the probable outcomes of neuter/return programs for either street dogs or feral cats in many different communities and parts of the world. Assuming a situation in which no newcomer dogs or cats can enter a specific habitat occupied by 100 street dogs or feral cats, the first column below shows the expected population changes if 70% of the animals are killed each year. The second column shows the expected changes if 70% are sterilized in a one-time sweep, with no follow-up. The third column shows what happens if 70% of the animals are sterilized each and every year. Each model presumes 1.5 surviving offspring per surviving adult of either gender per year, and 25% mortality among the adult animals. Street dogs on average have fewer but larger litters than feral cats, and more pups survive, so that the net rate of population increase per year is roughly the same for either dogs or cats.
Kill 70% 70% s/n once 70% s/n
Start 100 100 100 Year 1 25 77 76 Year 2 28 63 63 Year 3 32 56 49 Year 4 36 51 41 Year 5 41 48 31 Year 6 46 44 24 Year 7 52 45 18 Year 8 59 46 9 Year 9 66 49 6 Year 10 74 55 2 Year 11 83 60 1 Year 12 93 67 – Year 13 105 74 – Year 14 118 84 – Year 15 133 95 – Year 16 150 107 – The population in the killing model takes 13 years to rebound, but begins rebounding immediately. The population in the one-time sterilization sweep model declines until the number of reproducing animals exceeds the number of survivors in the treated population. Then the population recovers. However, because the breeding portion of the population for several years remained less than was needed to replace mortality, the dog or cat population in the one-time sterilization sweep model never catches up to the rate of population growth in the killing model. The third column above shows what happens if the sterilization rate is kept at 70% by sustaining the program year after year. In real life, immigration of animals facilitates faster population recoveries, but the trends are similar, just over a shorter time span. Taking this into account, Klinge compressed her model into an eight-year time frame, instead of the 16-year time frame above, and did not project that the street dog population could ever be reduced to zero. ––Merritt Clifton