Reduction of free-roaming cat population requires high-intensity neutering in spatial contiguity to mitigate compensatory effects

Abstract

Significance Although popular companion animals, domestic cats pose numerous problems when free-roaming, including predation of wildlife, hazards to humans, impaired sanitation, and a decrease in their welfare. Thus, managing their populations is essential. The trap–neuter–return method (TNR; capturing, sterilizing, returning/releasing) is widely employed for managing cat populations. However, there is a lack of long-term controlled evidence for its effectiveness. We examined the outcomes of high-intensity TNR by performing a 12-y controlled field experiment. Neutering over 70% of the cats caused population decline when applied over contiguous areas. However, it was limited by a rebound increase in reproduction and survival. These findings provide a robust quantification of the limitations and the long-term effectiveness of TNR.

Intensive Adoption as a Management Strategy for Unowned, Urban Cats: A Case Study of 25 Years of Trap–Assess–Resolve (TAR) in Auckland, New Zealand

“… Feature TE TNR TAR Speed of population reduction Rapid extirpation in closed populations but needs reapplication if abandonment or migration replenishes cats [ 37 , 87 ]. Some local successes are claimed, especially where populations are closed and there is high adoption within the program (e.g., [ 92 , 93 ]); however, Gunther et al [ 60 ] observed that achieving sterilization rates of at least 75% (required for population decline) is ‘almost impossible to reach and sustain on a meta-population scale.’ Gunther et al [ 46 ] reported population reductions of approximately 7% per year following high intensity (>70% neutering) maintained across contiguous sites covering a 20 km 2 urban area. Should be rapid in a closed population because cats are removed.…”

“… Should be rapid in a closed population because cats are removed. Needs reapplication when numbers are replenished by migration or abandonment, similar to the problems noted for TE and for TNR that are not applied across contiguous areas simultaneously [ 46 ]. Addresses problems caused by stray cats Yes, if applied at a level that reduces populations.…”

“…Neutered cats are less likely to fight or cause nuisances [ 6 , 63 ]. They still hunt, though, so that problem is unaddressed [ 25 , 26 , 46 , 94 ]. Some cats are adopted, gaining lasting care.…”

“…Trapping and euthanizing cats (TE) [ 37 , 44 ] sometimes meets with community resistance. There has been a growing number of literature reports describing alternative actions for potentially resolving stray cat issues, especially regarding trapping, neutering, and returning cats to the site of capture, e.g., trap–neuter–return (TNR); with variants such as TNVR (where cats are vaccinated before release) or TTNR (where there is intense targeting of a restricted geographical area), e.g., [ 45 , 46 ]. These methods entail varying degrees of follow-up support, including substantial time and money invested by ‘caretakers’ for these cats.…”

Emerging laws must not protect stray cats and their impacts

“…Moreover, it prohibits their elimination, replacing culling (which has successfully eradicated cat populations on certain islands; Nogales et al, 2004) by fertility control (Trap-Neuter-Return/ Release, TNR), which is considered more ethical. However, TNR only enables population reduction when applied at high rates over long time-frames and in spatial contiguity, at very high costs, and with compensatory effects that should be simultaneously managed (Gunther et al, 2022). Such complex, frequently unaffordable management would result in TNR perpetuating or even increasing the already high number of stray cats in cities and rural areas, thus maintaining (in the short-term) and then boosting (over longer time frames) their devastating impacts on biodiversity.…”