Presently, there are three approaches to surveying for seabirds: land-based (e.g. cliff counts), ship-based, and aerial. All three methods have advantages and disadvantages but when planning, a combination of all three can be used, depending on study objectives and budget, though cliff counts mostly restricted seasonally.
Seabird surveys generally examine trends in populations and distribution. Such information is relevant especially with regard to the development of offshore windfarms. Surveys prior to, during and following the construction of windfarms yield insights into habitat usage and potential/actual collision risks.
Seabird surveys at sea
European standardised seabird survey techniques have been reviewed by Camphuysen et al. (2004) http://jncc.defra.gov.uk. A number of factors need to be taken into consideration when planning seabird surveys from a vessel: transect design, including orientation and spacing, vessel selection, and, observer and equipment requirements.
Transect design should be based upon available knowledge of the survey area, including hydrography, topography, and seasonal expected bird densities. Survey vessels should be equipped with a stable, forward-facing observation platform, ideally as high above sea level as possible (within reason). Additional vessel specifications state that boats should be motorised. Inshore surveys are best carried out by smaller, manoeuvrable vessels (www.surveyvessel.co.uk), capable of being launched from a trailer to avoid spiralling standby costs of vessels forced to remain at sea during adverse weather conditions. Offshore surveys are best carried out by larger vessels >20 m in length, capable of accommodating crew and surveying larger areas.
At minimum, two trained observers, with good identification skills, should be used per platform of observation. Information on how to become a trained observer can be found at http://jncc.defra.gov.uk. Equipment required for surveys include binoculars, a GPS, range finders, and paper recording forms.
Strip or line transects with snap shots is currently the recommended survey methodology. This method allows short stretches of water of known surface area to be monitored effectively. Whilst on transect, vessel speeds should remain between six to 15 knots.
A species form needs to be filled in for every sighting whilst on watch. Details required for each sighting include:
- Number of individuals present;
- Whether the animal is ‘in transect’ or ‘not in transect’;
- Behaviour (swimming or flying);
- Distance from the ship;
- Plumage, moult, age, and sex of the bird;
- Flight direction; and,
- Notes (any additional information).
The behaviour of birds in proximity to wind turbines is still not well understood, though information is slowly becoming available for some species.
There are various approaches to assessing collision risk, namely:
- Evaluating theoretical number of collisions, which would occur if birds take no avoiding action; and,
- Applying an avoidance factor, which accounts for the fact that in reality, birds often succeed in dodging turbine blades.
Around windfarms, data on flight heights and behaviour are therefore collected in addition to collision-risk modelling and standard transect protocols.
Aerial line transects are most often used for distance sampling (http://en.wikipedia.org). A full description of these survey methods can be found at http://jncc.defra.gov.uk. Aerial surveys can be beneficial, as they are capable of reaching areas that are inaccessible by boat, and cover large areas in a shorter time frame. A disadvantage to aerial surveys is that they are expensive, must be carried out in very calm sea conditions, and it can be difficult to ascertain certain species and details on behaviour. It is for these reasons that boat and aerial surveys are most often carried out in conjunction.
Seabird breeding colony surveys
Separate survey methods have been written for surveying and monitoring breeding seabirds. A copy of the handbook, which contains detailed survey methodologies can be found at http://jncc.defra.gov.uk. Seabird breeding colony surveys estimate breeding numbers/success, and population changes. These results are often combined with other surveys to better understand how seabird populations are changing, or how they might be affected by changes in their environment.
Marine mammal surveys
Seabird surveys are often carried out in conjunction with marine mammal surveys by experienced and appropriately-qualified dedicated Marine Mammal Observers (MMOs; www.marinemammalobserver.co.uk) and Passive Acoustic Monitoring (PAM; www.passiveacousticmonitoring.com) operators. Marine Mammal Observers record visual sightings during hours of daylight and good visibility. Passive Acoustic Monitoring operators use specialised PAM equipment, such as towed hydrophone arrays (www.towedarray.co.uk), to detect marine mammal vocalisations. Passive Acoustic Monitoring can be used during all hours of the day (including night time) and during times of reduced visibility.