Evaluating population sizes and capture e

Over the last 12 years since I last posted on this thread...(is that possible? where did the time go?)

In Surrey, we have over 100 reptile sites that we've been systematically surveying for almost 10 years (>50K data points). Detection rates for each species vary dramatically by site. I've been trying to correlate the frequency of sightings to conservation status (population dynamics), but I can't do it from sightings alone.

Where habitat has been degraded, you see more animals (less cover to hide in...until they're predated), so that's a negative correlation. There are also year on year fluctuations. Almost the only useable sighting metric is peak count, as there must be at least that many of any species present. It's just not a very useful metric.

You can get population estimates from mark-recapture, which we do for all smooth snakes and increasingly for adder (using at-distance photography for Vb). The practicable solution is going to be a combination, using population modelling based on mark-recapture factors (weightings), probably on a site by site basis. We're not there yet, but we are closer than we've ever been.

A better route may be to look at the area occupied by a species, as this seems to be a far more stable measurement. We're probably too hung up on numbers, although habitat 'quality' for the occupied area is clearly important.

My 2p.

And you come across individuals like this that has just lost some of his tail but otherwise looks to be in good health...

Gemma / Karen,

Hi Everyone

Would it be possible that chosen methods for evaluating pop. size if standardised across the country might prove misleading?

I'm thinking of refugia, ground temp, air temp etc. and wondering if any of you who have worked in both the warmer and cooler counties might have noticed distinct differences in reptile visibility that could lead to misleading evaluations.