Wednesday, February 10, 2016

Does climate change increase the rate of feline reproduction?

Kittens: They grow up faster than you think.

The short answer: we don’t know.

The slightly longer answer: yesterday Kristina Vesk, CEO of the Cat Protection Society (CPS), and I were interviewed on ABC News 24 by KumiTaguchi about a reported association between an increase in temperatures during the winter months and an increase in the intake of kittens by the CPS. Traditionally there was a distinct “kitten season”, usually spring, but CPS has noted a trend in its data saying that “season” is much longer in years where winter temperatures are warmer. Which is a problem, because already there are too many cats without homes.

As CPS acknowledge, there are limitations with this data. This is a trend, and does not prove that climate change means more kittens. In fact, adverse weather events may increase kitten mortality, particularly neonates that have less ability to thermoregulate. In Sydney, for example, minor flooding is common. Many litters are born in drains and in heavy rain they may perish. We don’t really know, as CPS CEO Kristina Vesk pointed out, there is no census of homeless cats and kittens (despite the fact that cats and kittens continue to rule the internet, they have not yet mastered its use). We also don't know how well an increase in admissions to CPS correlates with overall cat population numbers. It may be in fact that during those years where spikes were recorded, there was a spike in good samaritans. The data has not yet been subjected to statistical analysis, although the hypothesis that climate change alters reproductive rate is biologically plausible. 

What we do know is that changes in climate and photoperiod can impact on feline reproduction, although no one fully understands exactly how. We also know that there are too many cats killed in Australian shelters because they cannot find homes. To this end, early-age desexing and the practice of adopting cats and kittens from shelters are more likely to impact feline numbers than any interventions directed at climate change, even if a link is proven. Some owners still don’t realise that cats can become sexually active early in life, and that the gestation period is only around two months. One female cat can produce dozens of kittens in her lifetime.

It is, however, worth considering how climate change impacts animals more broadly. The Australian Veterinary Association has a draft policy on Climate Change and Animal Health, Welfare and Production (published in the January/Feburary 2016 AustralianVeterinary Journal). AVA members are invited to comment on the policy by March 25. Significantly, it states that the AVA “supports the science of climate change and accepts that human activity is contributing to climate change”. The policy acknowledges that there is more scope for veterinarians to support and participate on research on the impact of climate change on animal health, welfare and production.

Key areas where animals are impacted by climate change include:
  • Changes in the habitat of native fauna
  • Changes in the epidemiology and distribution of vector-borne diseases (in small animals this includes diseases like heartworm (dogs and cats) and calicivirus (rabbits), which are spread by mosquitoes).
  • Changes in the potential for spread of arboviruses and henipahviruses
  • Pasture growth and nutrition

All of the above changes will also impact human health and well-being.

At a practice level we’ve seen the loss of a distinct “tick season”, with paralysis ticks – traditionally favouring the warm months – being found on dogs and cats even in winter. In addition, we’ve seen and heard of a lot more cases of heat stress in animals in the Sydney area. It is hard for owners to plan for marked and unpredictable variations in temperature. Watch this space.

If, in the meantime, you're teetering on the brink of adopting a cat, this post may just tip you over.

1 comment:

  1. Goodie - I've been waiting to jump on this:
    1. Insufficient data to make such a claim. Interesting hypothesis worth exploring.
    2. The CPS kept on quoting data on the high number of kittens they had in the Winter of 2013 - was this replicated in 2014 and 2015, which were sequentially hotter days?
    3. There is scope to review this hypothesis by examining the last 6-10 years worth of data and overlaying it with climate variation. Could there be a correlation between greater temperature variation over a month and subsequent kitten intake ~2 months later?
    4. Confounders - could there be an increasing in feral/stray cat densities associated with increasing human populations? While climate has the potential to be a factor, I still have yet to find any data to back that. The best I could find were a couple of papers - http://www.ncbi.nlm.nih.gov/pubmed/23279465 and http://www.ncbi.nlm.nih.gov/pubmed/22024367 that suggest that while cats closer to equatorial regions do still go into oestrus during the shorter day periods, they are a significantly smaller group than those during the extending days.

    Yes, more research is required.

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