Blog by Simon Wotton, Senior Conservation Scientist, RSPB Centre for Conservation Science

Today we are releasing the result of the fifth complete national survey for hen harriers, which was carried out across the UK and the Isle of Man in 2016.

The last national survey of this UK red-listed species of conservation concern was in 2010, when the population was estimated at 662 territorial pairs (95% confidence intervals giving a range of 576–770) this was an 18% decline in the population between 2004 and 2010.

Image: The trends in numbers of territorial pairs from the first national survey in 1988/89 to 2016, in England, Northern Ireland, Wales and the Isle of Man

Image: The trends in numbers of territorial pairs from the first national survey in 1988/89 to 2016, in Scotland and the UK

The aims of this new survey were to: 

• provide updated estimates of population size;
• identify trends since the last survey, nationally and regionally;
• provide data for further analyses of drivers of change in the hen harrier population.

This new survey shows that hen harrier population has suffered a decline of 88 pairs (13%) over the past six years with a total UK population estimated to be 545 pairs. Scotland remains the stronghold for UK hen harriers with an estimated 460 pairs in 2016, around 80 per cent of the UK population. You can read more about the results here.

In this blog I want to share the story of the work that led to these result. Because organising a full national survey of a (potentially) wide-ranging species across the UK does take a lot of time, and it is so much more than analysing the results and producing a final report.

Photo: Hen harrier  female in flight, image by Mark Thomas ( 

Planning a national survey
Before planning can even start, we need to make sure funding is agreed with one or more of the statutory agencies and, in with some other surveys, other governmental agencies and local authorities. We then need to define the breeding range that we need to survey and that involves requesting and collating data from a number of sources, and discussions with other groups. This discussion continues when much of the fieldwork is being carried out by volunteers, in the case of the hen harrier survey this is mainly though raptor study groups.

For this national survey we needed some paid field staff and this started in December. As we recruit staff we also have to arrange for hire vehicles, accommodation, risk assessments and other Health & Safety arrangements

For this survey, planning began in Sept 2015 and involved a number of survey partners. We defined, the survey area, which is the species current known breeding range, at the 10km square level, using results of the last survey and the Bird Atlas 2007-11 (data from BTO), in consultation within the RSPB, with the statutory conservation agencies, other organisations, and with raptor and upland bird study groups for their knowledge and details from the “core areas” that they usually monitor.

In Scotland (which holds the bulk of the UK’s hen harriers), the survey was organised by the RSPB, the Scottish Raptor Study Group (SRSG) and Scottish Natural Heritage. As the survey area in Scotland is too large to be able fully to cover in an annual survey like this, it is necessary to follow a robust sampling protocol. Each 10km square in the survey area was classified as belonging to one of two different categories so that the sampling approach is more efficient, based on recent records and habitat suitability. Survey coverage was organised in coordination with the SRSG and their members and other volunteers selected their 10km squares for coverage. From the remaining 10km squares, a stratified random selection of squares was surveyed by six RSPB fieldworkers. Within each category, a similar proportion of squares were randomly selected within each region to ensure that robust population estimates could be produced.

Elsewhere, we achieved comprehensive coverage within the Hen Harrier range in England, Wales, Northern Ireland and the Isle of Man. In England, coverage of suitable habitat in the potential range (mainly) across northern England was mainly carried out by raptor and upland bird study groups affiliated to the Northern England Raptor Forum, other upland bird study groups, and staff and volunteers from Natural England (NE) and RSPB. Additionally, any records reported through the RSPB Hen Harrier Hotline or the Moorland Association protocol with NE, were incorporated following appropriate validation. In Wales, comprehensive coverage of all of the 10km squares in the defined breeding range was carried out by two fieldworkers employed by RSPB, raptor study group members, and staff and volunteers from RSPB and Natural Resources Wales. In Northern Ireland, comprehensive coverage of the 10km squares in the defined breeding range was carried out by members of the Northern Ireland Raptor Study Group (NIRSG). RSPB provided additional funding to the NIRSG to ensure that more remote areas in Northern Ireland were fully surveyed in 2016. There was full coverage on the Isle of Man, with most of the surveying undertaken by a fieldworker who was joint-funded by Manx BirdLife and RSPB.

Photo: Male Hen Harrier, by Andy Hay ( 

The fieldwork
The field surveys followed the same methods used in the previous national hen harrier surveys, taking place between late March and the end of July. Suitable habitat for hen harrier is moorland, both heather and grass dominated, and upland young forest and we surveyed all such habitat within each 10-km square. In particular, observers were alerted to the possibility of birds nesting within closed mature coniferous forest, and to consider such areas as suitable habitat. Surveys were conducted through a combination of searches and scanning suitable habitat from appropriate vantage points. If a survey square contained a lot of potentially suitable habitat for breeding harriers, it could take three to four days to complete one visit, particularly in some of the more remote areas in Scotland. Survey forms were sent out to all participants, based on the forms used in previous surveys. It’s important to say that all fieldworkers have the proper licences from the appropriate statutory agencies. An important part of my job during the survey is to keep in touch with other fieldworkers, and it is always good to hear about their sightings, either of harriers, or other interesting bird and mammal sightings.

I carried out some of the fieldwork myself, on Orkney, in the Flow Country and in mid Wales. It was fantastic to be able to spend some time surveying, and finding hen harriers, on Orkney, where there are the highest densities of breeding harriers in the UK, and in the remote wilderness of the Flow Country. I wasn’t as lucky in Wales where I wasn’t able to find any harriers during my surveys.

Fieldwork can be very tiring, but for me the real hard work was just about to start at the end of season. There is a lot more work to do as I received all of the completed survey forms by the end of 2016. I entered all the data into a survey database and mapped on to a GIS system, and that’s when, for the first time, I can define the final number of ‘confirmed’, ‘probable’ and ‘possible’ hen harrier territories in each survey square, and then to produce the final population estimates by country and also by Scottish regions.
It is great to be able to share the results of this important survey. The next stage now is to produce a full report on the paper, which we will aim to publish in Bird Study later in the year.

The survey would not have been possible without the dedication of the members of the raptor and upland bird study groups across the UK as well as volunteers and staff from RSPB and the statutory authorities. Thanks go to all the Scottish Raptor Study Group, the Northern England Raptor Forum, the Northern Ireland Raptor Study Group and all other raptor and upland bird study groups in England and Wales who helped to organise and took part in the survey, and to the RSPB fieldworkers. Thanks go to landowners and estate managers for access arrangements. Thanks to SNH, RSPB and NRW for funding the survey.

  • Sadly I predict they will be extinct within 5 years unless there is some way to persuade people like the National Trust to go into partnership with the RSPB to manage part of the moors for a safe breeding area instead of using them for Grouse shoots.

    And before anyone says they don't stay on the same moors as they get older so would still be at risk we do a lot of work to help Turtle Doves who get blasted out of the sky as the migrate...come one RSPB and National trust get your acts together.