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DISTANCE-SAMPLING  April 2012

DISTANCE-SAMPLING April 2012

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Subject:

Re: using distance at wind farms

From:

Alvariza <[log in to unmask]>

Reply-To:

Alvariza <[log in to unmask]>

Date:

Wed, 4 Apr 2012 10:53:35 +0200

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Dear Tiago and all,
Many thanks for these contributions. Yes, I've read the paper you suggested; you refer many times the (our) problem, using distance sampling without a random design. But, as our aim is to detect changes in density estimates before and after construction of wind farms, and we start with a very heterogeneous methodologies (as much as the high number of human teams that do bird monitoring at a regional scale, at northwest Spain), we are going to continue at least considering DISTANCE as a tool, accessible to all and relatively easy to use for basic estimations, promoting also survey designers to locate better their line transects. However, we are going to take some time considering it, reading literature and asking experts, so we keep open this door to receive more comments/suggestions.

Thank you at all
Best regards,
Marta  


981 88 49 08 / 649108555
[log in to unmask]
www.alvariza.es
twitter: @alvariza_info

> -----Mensaje original-----
> De: Wildlife abundance estimation using distance sampling techniques.
> [mailto:[log in to unmask]] En nombre de Tiago
> Marques
> Enviado el: martes, 03 de abril de 2012 10:58
> Para: [log in to unmask]
> Asunto: Re: [DIST-SAMP] using distance at wind farms
> 
> Dear Marta, list,
> 
> It is unclear to me what are the exact characteristics of your study, but
> here is some general advice.
> 
> If one is trying to estimate density or abundance from conventional
> distance sampling and the transects are not placed at random in the
> landscape, for which examples might be:
> 
> transects along roads
> transects along rivers
> transects along altitude contours
> point transects from shore (looking at sea for cetaceans or birds say)
> 
> then density estimates will be biased if the distribution of animals with
> respect to the features used to lay the transects is not uniform.
> 
> This is because conventional methods assume that the distribution of
> animals with respect to the transects is known (uniform in the case of line
> transects, and triangular in the case of point transects), and that is
> enforced by design, using a large number of transects placed at random
> with respect to the animal distribution.
> 
> If your transects are placed along any type of landscape features, and
> the animal distribution is not independent of these, then you could get
> severe bias.
> 
> You can check here an example with points along roads, where bias was
> larger than 100% if ignoring the animal distribution:
> 
> Marques, T. A.; Buckland, S. T.; Borchers, D. L.; Tosh, D. & McDonald, R. A.
> Point Transect Sampling Along Linear Features Biometrics, 2010, 66, 1247-
> 1255
> 
> This paper also describes a way to deal with this issue at the analysis stage
> under a particular setting, but I would really recommend you avoid the
> problem by design whenever possible. This is because the information in
> the data is not enough to adequately separate the process of availability
> and detectability, and hence, unless you have independent information
> about one of these processes, they are confounded and you can't
> confidently estimate either of them, which precludes you to get robust
> density estimates.
> 
> Cheers
> 
> Tiago
> 
> On 03/04/2012 08:40, Marta Arenas wrote:
> > Good morning, Reading a recent discussion about hunting trails, a
> > thought arises about the suitability of Distance in monitoring work
> > at wind farms. We are trying to standardize these surveys and
> > Distance seems to be a good tool to do it, because it would eliminate
> > variations when calculating parameters. But, although the
> > recommendation is to place transects in paths or minor roads in the
> > area but outside direct influence of wind turbines, some (or many)
> > times they are already designed along the main roads (with wind
> > turbines). Then, should we discard its use in these cases? Any
> > suggestions? Thank you very much in advance,
> >
> > Marta Arenas ALVARIZA Asistencia Técnica Ambiental
> > [log in to unmask] www.alvariza.es
> >
> > -- distance-sampling list home page:
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> > [log in to unmask] --
> >
> >
> >
> 
> --
> ___________________________________________________________________
> _________________________________
> 
> Tiago André Marques
> Research Unit for Wildlife Population Assessment
> Centre for Research into Ecological and Environmental Modelling
> University of St Andrews
> The Observatory
> Buchanan Gardens
> St Andrews
> Fife KY16 9LZ
> Scotland
> 
> Tel: 00441334461842 Fax: 00441334461800 (Scotland office)
> Tel: 00351210198736 (Portugal home)
> 
> http://www-maths.mcs.st-andrews.ac.uk/homepages/tam2.html
> http://www.creem.st-and.ac.uk/tiago/
> 
> The University of St Andrews is a charity registered in Scotland : No
> SC013532
> 
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> --
> -----
> Se certificó que el correo no contiene virus.
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> Versión: 2012.0.1913 / Base de datos de virus: 2114/4910 - Fecha de la
> versión: 02/04/2012

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