Hi Nabin I think you'll also need to account for or show there was no interannual variation in factors that might affect observability/detectability (e.g. habitat changes). See David Anderson's views on such indices - http://warnercnr.colostate.edu/~anderson/free_index_values.html
Cheers Matt Dr Matt Hayward Regional Ecologist, Australian Wildlife Conservancy PO Box 432, Nichol's Point, Victoria 3501 -----Original Message----- From: Kurt Rinehart <[email protected]> To: ECOLOG-L <[email protected]> Sent: Wed, Feb 20, 2013 7:35 am Subject: Re: [ECOLOG-L] Abundance estimate references I don't know of anyone doing this, per se. Reporting a maximum count is often reported as the "minimum number known alive" (MNKA) at a given point in time. That might be the best you can do-be cautious of over-reaching from counts to abundance. Counts are typically adjusted for the observation process (imperfect detectability). It seems that by averaging your counts, you are trying to account for the observation variation, but abundance for your bird population isn't the same as bodyweight. You would average a sample of bodyweights to estimate the mean bodyweight of the population. Abundance is different. The "true" abundance is not some value between your highest and lowest counts, it is some value greater than any and all of your counts. Your average count is going to be a poor "estimate" of abundance. It is an estimate of your expected count given some true abundance--and that true abundance would have to be constant across the set of counts you are averaging for that to be sensible. Some use counts as indices of abundance. This interpretation requires assumptions about the constancy and uniformity of the observation process across all relevant counts and any others that you may wish to compare. The index interpretation may be suitable if your surveys controlled sufficiently for reasonable sources of observational bias. For an endangered bird in particular, this may be adequate--it depends a bit on how much is known/inferred currently of the species' abundance. For a quick treatment, this document and references therein seems pertinent: http://www.ebcc.info/wpimages/other/birdsurvey.pdf On Tue, Feb 19, 2013 at 11:34 AM, Nabin Baral <[email protected]> wrote: > Hello Ecolog Members: I've recently submitted an article about population > size estimate of an endangered bird species. I counted birds during the > breeding seasons at least five times per season for 10 years. For the sake > of comparison, I have also included the mean and the highest count as an > estimate of abundance. One of the reviewers is asking to include references > of other studies or methodological articles about the convenience or > advantages of using the mean or the maximum value of a series of counts. I > have searched online, but could not locate appropriate citations/articles. > I hope that someone in the list might help me about the references. > > Please reply me off list if you know any references in this area. Thank > you in advance for your time. > > Sincerely, > Nabin >
