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Modelling the abundance and distribution of marine birds accounting for uncertain species identification
Johnston, A., Thaxter, C.B., Austin, G.E., Cook, A.S.C.P., Humphreys, E.M., Still, D.A., Mackay, A., Irvine, R., Webb, A. & Burton, N.H.K. (2014) Journal of Applied Ecology ():-
- Many emerging methods for ecological monitoring use passive monitoring techniques,
which cannot always be used to identify the observed species with certainty. Digital
aerial surveys of birds in marine areas are one such example of passive observation
and they are increasingly being used to quantify the abundance and distribution of
marine birds to inform impact assessments for proposed offshore wind developments.
However, the uncertainty in species identification presents a major hurdle to
determining the abundance and distribution of individual species.
- Using a novel
analytical approach, we combined data from two surveys in the same area: aerial
digital imagery that identified only 23% of individuals to species level and boat
survey records that identified 95% of individuals to species level. The data sets
were analysed to estimate the effects of environmental covariates on species density
and to produce species-specific estimates of population size.
- For each digital
aerial observation without certain species identification, randomized species
assignments were generated using the observed species proportions from the boat
surveys. For each species, we modelled several random realizations of species
assignments and produced a density surface from the ensemble of models. The
uncertainty from each stage of the process was propagated, so that final confidence
limits accounted for all sources of uncertainty, including species identification.
- In the breeding season, several species had higher densities near colonies and
this pattern was clearest for three auk species. Sandeel density was an important
predictor of the density of several gull species.
- Synthesis and applications.
This method shows it is possible to construct maps of species density in situations
in which ecological observations cannot be identified to species level with certainty.
The increasing use of passive detection methods is providing many more data sets
with uncertain species identification and this method could be used with these data
to produce species-specific abundance estimates. We discuss the advantages of this
approach for estimating the abundance and distribution of birds in marine areas,
particularly for quantifying the impacts of offshore renewable developments by
making the estimates derived from the older digital surveys more comparable to the
recently improved surveys.
environmental impact assessment,
high definition imagery,
offshore wind farm,
uncertain species identification
Links at this site
- Northern Fulmar (Fulmarus glacialis)
- Northern Gannet (Morus bassanus)
- Black-legged Kittiwake (Rissa tridactyla)
- Lesser Black-backed Gull (Larus fuscus)
- Great Black-backed Gull (Larus marinus)
- Common Guillemot (Uria aalge)
- Razorbill (Alca torda))
- Little Auk or Dovekie (Alle alle)
- Atlantic Puffin (Fratercula arctica)
- Sandeel (Ammodytidae)
- abundance modelling
- environmental impact assessment
- high definition imagery
- offshore wind energy development
- passive monitoring
- renewable energy
- sea surface temperature (SST)
- uncertain species identification
- Dogger Bank
- North Sea
Links to other sites