Distance sampling at sea for seabirds; best practice and tips

[vaughn...@gmail.com]

Hi 

I work in the Cayman Islands with the local Dept. of Environment on the terrestrial ecology team. We have an opportunity to survey for seabirds in the greater EEZ (territorial waters) on a research vessel. Unfortunately, we can't plan the route as there are a lot of other research interests on board but we will survey at set times and use the ship travel route during those times to determine transect location and length (or point locations for surveying when stationary). We'd like to make the most of this opportunity to understand what species use the EEZ and in what numbers. 

We have a lot of experience implementing distance sampling surveys on land but none at sea. 

Does anyone have any field survey guidance documents or general best-practice tips for implementing distance sampling surveys at sea? or thoughts on the lack of formal survey design. But we are especially interested in any tips on measuring distance accurately using range finders.

I am not conducting the field work but I am advising on methods.

Any help is appreciated! 

[Eric Rexstad]

Vaughn

There is a body of literature describing field methods associated with seabird surveys. The ESAS (European Seabirds at Sea) protocol is often used.  Others may have additional data gathering advice for you

• Camphuysen, C. J., Fox, A. D., M.Leopold, and I. K.Petersen (2004). Towards standardized seabirds at sea census techniques in connection with environmental impact assessments for offshore wind farms. U.K. COWRIE 1 Report. Royal Netherlands Institute for Sea Research, Texel, Netherlands.
• https://tethys.pnnl.gov/sites/default/files/publications/Camphuysen-et-al-2004-COWRIE.pdf

The other issue of non-random transect placement means convention distance sampling based partially upon design-based inference cannot be employed. Rather a two-stage model-based approach would be needed; there is the traditional model for the detection process, but also a model to infer encounter rates as functions of environmental covariates.  There are a few examples of applying this methodology to seabirds:

• Wakefield, E. D., Miller, D. L., Bond, S. L., le Bouard, F., Carvalho, P. C., Catry, P., Dilley, B. J., Fifield, D. A., Gjerdrum, C., González-Solís, J., Hogan, H., Laptikhovsky, V., Merkel, B., A. O. Miller, J., Miller, P. I., Pinder, S. J., Pipa, T., Ryan, P. M., Thompson, L. A., … Matthiopoulos, J. (2021). The summer distribution, habitat associations and abundance of seabirds in the sub-polar frontal zone of the Northwest Atlantic. Progress in Oceanography, 102657. https://doi.org/10.1016/j.pocean.2021.102657
• Kristopher J. Winiarski, M. Louise Burt, Eric Rexstad, David L. Miller, Carol L. Trocki, Peter W. C. Paton, Scott R. McWilliams, Integrating aerial and ship surveys of marine birds into a combined density surface model: A case study of wintering Common Loons, The Condor: Ornithological Applications, Volume 116, Issue 2, 30 April 2014, Pages 149–161, https://doi.org/10.1650/CONDOR-13-085.1

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From: distance...@googlegroups.com <distance...@googlegroups.com> on behalf of vaughn...@gmail.com <vaughn...@gmail.com>
Sent: 21 October 2025 19:06
To: distance-sampling <distance...@googlegroups.com>
Subject: [distance-sampling] Distance sampling at sea for seabirds; best practice and tips

 

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[Vaughn Bodden]

Thanks for the information, Eric. I’ll review and let you know if I have any questions.

[Brendan Higgins]

Hi Vaughn,

We've had good luck using the vortex rangefinder binoculars. Another pretty common method for at-sea surveys involves measuring the distance of the bird below the horizon and doing some math. I couple resources:

Heinemann, Dennis. “A Range Finder for Pelagic Bird Censusing.” The Journal of Wildlife Management, vol. 45, no. 2, 1981, pp. 489–93. JSTOR, https://doi.org/10.2307/3807930. Accessed 22 Oct. 2025.

https://jncc.gov.uk/resources/e2a46de5-43d4-43f0-b296-c62134397ce4#Guide-making-rangefinder-stick-rev01-Web.xls

Hope this helps,

Brendan

To view this discussion visit https://groups.google.com/d/msgid/distance-sampling/CACccXiyJQSB_Q5_E6mKumjitqESjgdsV21wds2wK6VFtuiqY%2BA%40mail.gmail.com.

[Cornelia Oedekoven]

Hi Vaughn, 

You could also have a look at this paper: 

Ballance LT. 2007. Understanding seabirds at sea: why and how? Marine Ornithology 35:127-135.

where at sea surveys of seabirds using strip transect methods are described. These strip transects on NOAA surveys are often done alongside line transect surveys for marine mammals. 

In any case, for strip transects you only survey a small strip along the line, usually 300 m, on one side of the ship and record every bird that comes within this radius. The assumption is that you detect all birds within the strip.  This has the benefit that you do not need to record the distance from the line to every bird or bird flock (you would need to do this for line transects). You only need to know was the bird within the 300 m. Birds often occur in high numbers that it would be impossible to record all the birds you detect out to the horizon along with the distance information if you did line transects. 

This still leaves you with needing to judge the distance (=<300 m or not?) which is difficult at sea. There are tools available, such as binoculars with reticles or you can make your own range finder. Have a look at this paper: 

Heinemann, Dennis. (1981). A Range Finder for Pelagic Bird Censusing. The Auk. 98. 437-456.  

Cheers, Cornelia

><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <><

Cornelia S. Oedekoven, PhD

Senior Research Fellow

Centre for Research into Ecological and Environmental Modelling (CREEM)

cs...@st-andrews.ac.uk

creemmural.org

creem2.st-andrews.ac.uk

coedekoven.wix.com/cornelia-oedekoven

><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <>< ><> <><

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From: 'Brendan Higgins' via distance-sampling <distance...@googlegroups.com>
Sent: 22 October 2025 20:54
To: Vaughn Bodden <vaughn...@gmail.com>
Cc: Eric Rexstad <Eric.R...@st-andrews.ac.uk>; distance-sampling <distance...@googlegroups.com>
Subject: Re: [distance-sampling] Distance sampling at sea for seabirds; best practice and tips

 

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[Vaughn Bodden]

Thanks for the suggested reading and tips, Cornelia and Brendan. We are looking at options for getting binoculars or range finders that are designed for pelagic surveys, or we may resort to making the range finder stick, as suggested in the JNCC link sent. 

The expedition is planned for ~12 days. Is it best to survey in short 'snapshots' (e.g. 10 10-minute intervals) at some frequency throughout the day? What frequency is typical? Or are longer survey intervals more productive?

I've attached a map of the general route they plan to take around Grand Cayman and the focus areas. There are a lot of overarching research interests for this trip, but we will make the most of it for seabirds. The lack of formal survey design is still the main limitation, but hopefully that will change when all plans are finalised. For now, we plan to explore the two-stage approach using DSM modelling approach that Erik suggested. 

[mikhail soloviev]

Hello, Vaughn,

 

 

there is certain canadian experince of surveying seabirds:

 

D. A. Fifield, A. Hedd, G. J. Robertson, S. Avery‐Gomm, C. Gjerdrum, L. A. McFarlane Tranquilla, S. J. Duffy. 2016. Baseline Surveys for Seabirds in the Labrador Sea (201‐08S). Environmental Studies Research Funds Report No. 206. St. John・s. 69 pp.

 

 

The best,

 

Mikhail

 

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From: distance...@googlegroups.com [mailto:distance...@googlegroups.com] On Behalf Of vaughn...@gmail.com
Sent: Tuesday, October 21, 2025 9:07 PM
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Subject: [distance-sampling] Distance sampling at sea for seabirds; best practice and tips

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