Non-breeding walkover survey
When should this method be used?
This method is applicable where a full coverage of a site is required. This methodology is similar to the methodology for surveys of breeding birds and involves walking a transect that allows survey coverage of a site.
This methodology is applicable for terrestrial habitats that have the potential to support non-breeding priority bird species.
Although non-breeding bird surveys broadly follow the same methods as those undertaken during the breeding season, the species priorities are subtly different.
Surveys should seek to qualify the diversity of birds interacting with a land parcel, in the context of their specific ecology and population status. For example, where non-breeding mallards are generally not a survey priority during the breeding period, during the winter they are reliant on certain habitats for survival. Should these habitats be significantly disturbed or destroyed, those reliant birds are unlikely to reach breeding condition during spring.
Getting the appropriate level of survey effort correct is likely to be dependent on a range of site-specific factors.
Clearly a single visit is unlikely to provide a robust level of information. Whereas, the more visits undertaken, the more species you record, until, due to the law of diminishing returns, the species detection curve flattens out.
As standard it is recommended that monthly survey visits (i.e. one visit per month) be undertaken as part of a survey for non-breeding birds.
The number of visits will depend on the habitats present and the ecology of priority species that may occur on site. This will be determined by the desk study. For example, a site that is likely to support wintering birds may require monthly visits between November and February (the core winter months), whereas a site that has passage potential may require a wider window of survey (e.g., seven monthly visits between September and March inclusive). For particular target species the BTO bird track data can help identify periods of peak detectability, and this can inform the survey dates.
The number of surveys being undertaken must be supported with detailed and robust justification. Additional survey effort may need to be considered for large-scale projects with the potential to have significant impacts on birds, and/or for high profile, sensitive projects. On the other hand, fewer survey visits may be justified for projects with very limited impacts, or sites with habitats of low value for birds.
Additional surveys (such as Wetland Bird Survey, nocturnal survey, or species-specific surveys) should also be considered and will depend on the habitats present and the ecology of the priority species that may occur. For particularly large sites, surveys may require several surveyors.
Survey timing should always be about maximising detection of species likely to be present on site. Unlike during the breeding period, when many species are detectable primarily on call or song, during the non-breeding season, audible detectability of many species will decrease, and surveyors must rely on visual identification.
The behaviour of many species is also likely to move from breeding and territorial behaviours to foraging and resource acquisition, and so birds present may be more obvious for longer periods (although not always the case). Therefore, there is less restriction on timings of surveys, and the majority of non-breeding walkover surveys will be determined by visibility (i.e., undertaken during daylight hours).
The ecology of the priority species that may occur on site should be taken into account when considering the timing of surveys, and it may be necessary to vary the start time to incorporate dawn and/or dusk.
Please note that some sites may support priority species during the hours of darkness (for example if golden plover utilise arable fields overnight) and these may require nocturnal bird surveys. These are likely to be in addition to the non-breeding walkover surveys, rather than as a replacement.
Planning survey dates
The number of visits will depend on the habitats present and the ecology of priority species that may occur on site. For example, a site that is likely to support wintering birds may require monthly visits between November and February (the core winter months), whereas a site that has passage potential may require a wider window of survey (e.g. seven monthly visits between September and March inclusive). For particular target species, the BTO Bird track data can help identify periods of peak detectability, and this can inform the survey dates.
Factors to consider when planning survey times and dates:
- Weather conditions – has it been a particularly wet or cold season? For example, a mild winter may lead to later arrivals of wintering birds, whereas conversely a particularly cold snap early in winter may lead to earlier arrivals.
- Does your site have seasonally constrained features – such as temporary pools that might only be present early in the season or in wet years? If your survey coincides with a dry year you may underestimate the importance of a site or miss important birds such as lowland waders.
- Do you need data from more than one non-breeding season?
- Do you have reason to suspect species that are more readily detected by nocturnal surveys such as woodcock or golden plover?
Prior to starting the survey, record the date, start time, time of sunrise / sunset, temperature (°C), wind (Beaufort scale 0–12), cloud cover (Okta 0–9, ‘9 Okta’s represents sky obscured by fog or other meteorological phenomena’ and therefore is unlikely to be appropriate for a bird survey) and rain (as a brief description e.g., dry, light drizzle). The end time and closing weather conditions (if there has been a substantial change during the survey) should also be recorded.
The weather conditions are typically less restrictive during non-breeding surveys than surveys of breeding birds, and a range of weather conditions could actually help provide a representative assessment of the priority species present. However, typically surveys will need to be undertaken when there is good visibility, to enable the visual detection of priority species. If surveys are carried out in less-than-ideal conditions, this should be noted as limitation in the report, with justification and a consideration of potential impacts.
A survey transect should be walked at a slow, ambling pace, stopping to scan priority habitat/features where appropriate. Priority habitat/features could include (but are not limited to) open fields, trees, dense hedgerows or berry-bearing shrubs or small bodies of water.
One or more survey transects should enable visual coverage of the entirety of the site, but without excessive disturbance of the habitats on site. This will be determined by the terrain and habitats present. For example, large open fields may be possible to survey from one or two key locations, whereas dense woodland would require much greater coverage. Where areas within a site cannot be accessed, this should be noted in the report as a constraint to the survey.
Additional consideration should be given to any hazards identified in the site-specific risk assessment. Under no circumstances should observers enter into a hazardous situation in order to complete a survey. Instead, surveys of inaccessible or hazardous habitats should be undertaken from a vantage point or other safe distance, and any limitations should be recorded in the report, with justification and a consideration of potential impacts. Where appropriate, these hazards should be reported and any site specific risk assessment changed in light of this new information.
Care should also be taken to avoid causing damage to arable crops or disturbance to livestock present within a survey area. In these situations, it is acceptable for observers to keep to field margins or tram lines, but also consider a vantage point, or supplementary survey, from a reasonable distance.
Surveyors should be mindful of the zone of influence of the development scheme (i.e. the distance beyond the redline boundary that a scheme may still have an impact on breeding birds, either during construction or operation). Surrounding habitat (outside of the redline boundary) should also be surveyed to a reasonable distance – particularly land immediately surrounding the site itself, and any nearby potentially valuable habitat which is likely to be impacted by construction and/or operation (including but not restricted to waterbodies and woodland).
All species encountered on the site or adjacent land should be reported.
The approximate locations of priority species should be plotted on a site map together with behavioural notation where appropriate. Counts of secondary species should be recorded separately and based on the highest number of each species in a distinct location, being careful to avoid repeat counting of individuals.
Observations of birds moving high overhead, and not associating with the site itself, should be summarised together with recordings of secondary species or omitted all together. Exceptions should be made for those birds which fall under sections i., ii. or iii. of the Priority species hierarchy, are likely to associate with the site itself (e.g. gulls over arable farmland in winter), or those priority species which could be associated with habitats present (e.g. golden plover over an arable farmland site).