With their black, white and grey plumage and graceful flight on impressive wings, herons – or harnser – have an unmistakable silhouette in the air. This elegant bird inspired one of the world’s oldest wildlife surveys.

'With the number of competent observers presently available it seems possible to undertake a census of British Heronries on a more accurate basis than has up to the present been attempted… changes in recent years have been very considerable and ought to be recorded before it is too late… we are therefore including in every copy of this issue a schedule and a post card which we hope every reader of British Birds will fill up and return to the office.' (February 1928).

In the Norfolk dialect, particularly on the Broads, they were known as harnser or hanser.

With their striking black, white and grey plumage and graceful flight on impressive wings, their large size gives them an unmistakable silhouette in the air and as they wait with bright yellow eye and sharp, long bill on the banks of our rivers and in the reeds of lake margins.

Great British Life: Grey heron. Grey heron. (Image: Serena Shores)

They walk with confidence and inspire awe. Ardea cinerea, the grey heron, would also lead an Oxford Undergraduate with a passion for ornithology, to pioneer environmental conservation in an era when it was almost unheard of, creating one of the world’s first centrally organised scientific censuses of a species, started 96 years ago.

In early 1928, a young Max Nicholson (1904-2003), future conservationist and founder member of the British Trust for Ornithology (formed in 1933 and based in Thetford since 1991) may have been familiar with the organisation of amateur surveys, as a member of the Oxford Ornithological Society.

Ringing had begun around 1909, but the idea of a single national census was somewhat novel at the time. Nevertheless, Nicholson joined forces with the editor of British Birds, H. F Witherby, to advertise for volunteer enthusiasts to carry out a survey of the heron’s favoured nesting sites in tall trees. The census was also advertised in The Naturalist and The Field and was planned for the following April to May.

Great British Life: Ian Woodward. Ian Woodward. (Image: Serena Shores)

'Although the census wasn’t formally "run" in the years immediately following 1928, observers continued to submit data and the nest count gradually became established as an annual feature,' explains Ian Woodward, British Trust for Ornithology research ecologist and Heronries Census national organiser. 'Recording has gone from personal letters to the editor of British Birds, to the introduction of report cards in the 1950s and digitalisation in 2015.'

Numbers have gone up and down from 1928 when 3,800 nests were counted although recent estimates suggest nearly 10,000 pairs were nesting, through severe dips in the late 40s (to 7,250) and early 60s (to 6,900), attributed to harsh winters where the heron was unable to access prey in frozen bodies of water.

'With a peak in 2000 of 13,000, the breeding population has generally seen a long-term uplift since 1928, which continued up to the turn of this century,' says Ian. 'There are around 9,500 pairs of Grey heron today and overall the population has recently been relatively stable, but the BTO is keeping any eye on the trend as numbers have not recovered following a decline due to harsh winters from 2009-2011.'

Great British Life: Letters from the archive. Letters from the archive. (Image: Serena Shores)

Letters in the BTO’s archive demonstrate how many early respondents perceived the situation, following centuries of persecution and the destruction of heronries which might have been used for decades, by the felling of trees for timber during the Great War.

'It is stated that at Arle Trout Farm, 48 were shot during 1920-27 and odd birds shot by wildfowlers and keepers. The heronry at Avondale is annually raided by boys from the school.'

'If the estimates of 60 or 70 years ago are reliable, then it is doubtful any county will return so many this year for the time of the very large heronry is over…'

'I have known 30 nests but many trees have been blown down or cut down and now there are usually a dozen.'

Great British Life: Grey Heron at East Bank Cley Marshes. Grey Heron at East Bank Cley Marshes. (Image: Serena Shores)

'Habitat management work for water birds has likely benefited the grey heron, along with changing attitudes,' explains Ian. 'We must also remember that in 1928, the grey heron was the only heron species in the UK as the bittern was extinct at the time. From the 1990s, little egrets began to arrive in the UK followed subsequently by other egrets and heron-like species. Although the smaller little and cattle egrets probably don’t compete for food, the great white egret potentially could do and there could be possible competition for nest space from the cormorant which first started to nest inland in the 1980s. Hence, the potential future impact of colonising species on Grey herons is uncertain.'

In terms of ecology, it is rarely clear cut. Despite possible competition for resources between species, herons, egrets and similar species can form huge mixed colonies in Europe.

Great British Life: Grey heron. Grey heron. (Image: Serena Shores)

Mixed colonies are beginning to appear in the UK with one well-publicised example right here in Norfolk, at Holkham National Nature Reserve where spoonbill and other species, all nest alongside or near the grey heron.

'Today, surveyors are basically asked to record a count of the number of apparently occupied nests for each species for each visit,' Ian concludes. 'Harking back to a century ago, many volunteers will use a notebook rather than the recording form and amateur volunteers are welcome, although some counts will be made by reserve staff, in particular at sites where disturbance will be a potential issue'

Rather poignantly for the home of the BTO, Norfolk has always been difficult to record due to the terrain of wetlands and issues gaining access to wild areas. Nevertheless, that harsh ‘kraank’ call reverberates as it did a century ago, carefully monitored by this little-known army carrying out their careful research.