The calls of the first golden plover are ringing out over the hills again, hopefully a welcome sign that spring is on the way! Certainly a welcome thought for those carrying out golden eagle flight activity surveys above the snowline throughout the winter. The golden eagle is arguably one of Scotland’s most iconic birds due to its size, secretive behaviour and the connotations it has of wild, remote landscapes. Sadly in England, the last resident golden eagle in Cumbria failed to re-appear during the 2016 breeding season and is assumed to have died of old age; being around 20 years old, a fairly advanced age of an eagle. In Scotland, the picture is looking brighter – with results from the fourth national golden eagle survey during 2015 showing a 15% increase in number of pair from 2003, up to 508 pairs. This means the golden eagle is now classed as having “favourable conservation status” for the first time since the national surveys started.
Flight activity surveys or Vantage Point surveys (VPs) were originally devised by SNH as a methodology to assess bird collision risk with wind turbines. The survey requires the observer to scan a 180-degree arc up to a distance of 2km for a period of 3 hours. Any target species recorded flying within this area will be followed until they land or are lost from sight. The height will be estimated (within set height bands) and the number of seconds of flight time within each height band recorded, along with details such as the birds age and gender, where this is possible. Vantage point surveys themselves are a standard monitoring technique for wind farm developments and are used to compare the collision risk calculated before the development, with the collision risk calculated based on data collected once the wind turbines have been constructed.
In other situations, breeding raptor surveys may be more appropriate, such as for hydro schemes, grid connections or monitoring the impacts of habitat restoration on target species. The purpose of these is to ascertain the presence (or absence) of any breeding raptors and to monitor the outcome of any breeding attempts. A standardised methodology is generally followed involving typically four visits during the breeding season to areas of potentially suitable habitat. There is some variation in the specifics – due to differences in individual raptor species’ behavioural biology/ breeding behaviour. In the case of golden eagle, the first survey visit to check for territory occupancy can be carried out as early as January and late as March. Surveys would take the form of watching out over likely foraging areas or up towards ridges from a suitable vantage point.
The second visit is carried out during April in order to locates nests – all known eyries should be observed as the birds are quite site faithful with nesting sites. This should be carried out from a distance – 750m to 1.5 km away as Golden eagle are especially sensitive to disturbance immediately prior to and during egg laying. If previous eyries are not known, then suitable areas such as crags or trees – typically mature scots pine should be observed. Nests can vary significantly from gathered vegetation on a ledge, to considerable structures comprising sticks and heather, with a soft lining. It follows that the ease with which they can be detected at distance (without observing an eagle flying onto/leaving the nest) can also vary!
The eggs will be incubated mostly by the female, for 41-45 days, with the young spending a total of 70-80 days in the nest prior to fledging. Initially given the chicks small size it can be challenging to see them and the presence of chicks may need to be inferred from the adults’ behaviour – especially if the nest is a deep structure. As they grow, it may be possible to roughly age them based on their plumage development if the observer is able to get a good view during the penultimate survey visit in June.
The final visit would be made in July to check for fledged young – which tend to remain in the vicinity of the nest for a few weeks after fledging. Care should again be taken not to approach the nest as disturbance could result in premature fledging of the young eagles – which may result in injury or make them vulnerable to ground predators.