Welcome to the second instalment of RSPB Dearne Valley - Eye Opening

To follow the journey some of the key species in the Dearne Valley, I recommended that you read the first blog by following this link: 

#1 RSPB Dearne Valley - Eye Opening

Bittern in the Dearne Valley: Eggs and things:

The management of the reeds at Dearne Valley has led to fantastic success for bitterns, but it is also a success for other species too. 

In addition to watching the bittern, visitors to the Dearne Valley sites can also watch marsh harriers who have taken up residence in the same habitats as the bitterns; and have also been raising a new generation of this powerful bird of prey. 

Tragically, in 1971 there was only one nesting female marsh harrier in the UK; however, after a massive conservation effort the bird has made a comeback, with around 600 breeding pairs now in the UK.  The Dearne Valley has contributed to this success, with marsh harriers breeding here for the last 2 years, and over-wintering birds being seen more often. This gives us a brilliant opportunity to compare and contrast the two birds. We covered some key differences between the two species last time… this time its juveniles.

Four bitterns                                                                                     G Lax

Originally, bitterns were thought to need large areas of reedbed to support one nest, but this was disproved in 2018 when RSPB Old Moor had 3 nests on the go at the same time; less than 150 metres apart.  Bittern nests tend not to be a fancy pied á terre; more like a collection of reeds brought together to resemble a shelf, positioned just above the water in the reeds. If water levels rise, more material is added to raise the nest up.

Marsh harriers are more likely to build their nest on the ground in the reedbed, and increasingly in fields near marshes and wetlands; constructing it from reeds, twigs and any other grass-like material nearby. The male marsh harrier will also build fake nests nearby too, to try to prevent the true nest’s location being discovered by predators, such as mink, or otters.

Bitterns and marsh harriers have similar size clutches of eggs; the bittern has 4-6 eggs, whilst the marsh harriers will usually lay 4-5 eggs. Eggs are laid over a few days in both species; and they will usually only have one clutch of eggs a year, unless a clutch is lost, in which case a replacement clutch may be produced. However, for the last 2 years, it appears that a female bittern at Old Moor has “double-brooded”, which means she has incubated one clutch whilst feeding another – unusual and exciting, and you can read more about that in the Man in the Box article below!

Male marsh harrier                                                                                        G Lax

Bitterns will incubate their eggs for around 25 days: and marsh harriers for slightly longer, at 31-38 days. Hatching takes place, like egg-laying, over a number of days. Then, both species’ focus of attention is feeding the young until fledging takes place; for bitterns at around 55 days, and for marsh harriers at around 35-40 days, after hatching.

Whilst the male marsh harrier takes an active role in rearing the young (see the previous blog where “food-passes” are covered), bittern males are not involved in nest-building or rearing the young; and may father eggs in several nests. However, although male marsh harriers will bond with a female and take a very active part in feeding the young and the female, he may have bonded with 2, or even 3, females, and will look after them all, which can result in smaller clutches.

Bittern                                                                         G Lax

During that period, Bitterns are making feeding flights to and from various locations which hold food; and marsh harriers are making food passes in the air, and bringing food to the nest; and both birds are often spotted in and above the reeds until their young fledge.

Finally, the lifespan of bitterns is thought to be around 9-11 years, with female bitterns able to breed in their first year; whilst a marsh harrier is likely to last around 6 years. 

The Man in the Box:

Geralds hideaway, the Monitoring Hide                    J Mayston

The RSPB say; “monitoring is an essential component of management and planning.”  One of our own heroes, Gerald, is here at Old Moor almost every day, monitoring the activities of the bittern and marsh harrier. He is one of the unseen army of staff and volunteers who contribute to site maintenance and planning so that the success of both species continues. Here Gerald offers his view as “the man in the box”, and his review of 2020:

“It is difficult to believe but as little as just over 20 years ago there weren’t any reedbeds at Old Moor where they are now situated; only down at Wath Ings. They have been created and maintained by our knowledgeable and hardworking Wardening Team, assisted by intrepid volunteers, out in all weathers. Some of the reeds were grown in poly tunnels, others were imported from Blacktoft Sands, who were creating feeding pools for bitterns.

This work has resulted in now having three iconic reedbed species breeding at Old Moor; the bittern, the bearded tit and, during 2020, for the first time in the Barnsley area, marsh harrier.

In the reedbed the first signs of the new season begin as early as mid-February when the male bitterns begin ‘warming their tubes’, prior to the Booming, by giving out a faint grunting noise. In late February or early March the Booming begins in earnest with the males proclaiming their presence both to females and other males that may be competing for the females’ attention.

This year (2020), monitoring began as normal in early February. We established that we had several males on site, but when lockdown came towards the end of March 2020, no nest site(s) had been located. This was quite normal, as it is usually mid-April when several feeding flights have been seen that nesting can be presumed, and detail on the number of nests and their situation is acquired.

Juvenile marsh harrier                           G Lax

During lockdown, staff living on site used to walk to the monitoring hide as part of their allotted exercise, and during this time they suspected a bittern nest, and a marsh Harrier pair who appeared to have nested only about 100 metres from the bittern.

The female bittern, who was easily identifiable due to having missing primary feathers and a toe which hung down when she was flying, made feeding forays to many parts of the reserve, and Bolton Ings. First one, then another, young bittern with a fluffy ginger head appeared climbing the reeds. By late May it was established that there were 4 young from the first bittern nest.

At the same time, the male and female marsh harriers were going about their familial duties. The female marsh harrier doing all the incubation (31 to 38 days), whilst the male hunts for food and then passes it in the air to the female, or sometimes establishes a cache, which the female will go to, periodically.   It was noticeable that the female bittern would return to the nest to feed her young to avoid being harassed by the harriers whilst they were preoccupied with their feeding routine.

The marsh harriers were also taking reed back to the nest on a daily basis to keep the nest in good condition.  

Marsh harriers, like bitterns and owls, lay their eggs 2-3 days apart and begin incubating straight away, so there can be quite an age gap between youngest and eldest chick.

Therefore, when the first successful young was seen (with great joy) and then a second (more joy), the anticipation began, in waiting to find out how many they had managed to rear. It was not until 21st July that we eventually saw all 3 young rise from the nest, for food that their mother had brought for them.  It was a truly momentous and heart-warming sight.

The young, with their distinctive ginger heads, continued to be fed ever more increasingly by food-pass, rather than at the nest site, for some time until they were self-sufficient. As usual with young marsh harriers, they stayed around the reserve for a few months, delighting many viewers with their first views of young marsh harriers.

The female bittern continued to feed her young as they wandered about the reedbed, gradually further away from the nest site, some young were more adventurous than others!

Female Bittern with the missing primary feathers on the RH wing                    G Lax

About two and a half weeks after she had finished feeding flights for her young, a bittern was seen going to another site in a different reedbed on a regular basis, which is a sign of feeding flights. On closer examination, the bird had the same missing primaries and dangling toe, so it would appear to be the same bird. It is highly unusual for bitterns to double-brood, and it was felt that there had not been enough time elapsed between the two sets of feeding flights for the bird to have made a second nest and laid and incubated a second clutch, after the first clutch had fully fledged; so she must have been feeding the first clutch whilst incubating the second clutch, something which has possibly never seen before, and quite remarkable.

How could this have occurred? Usually, the female will make feeding flights with increasing regularity as the young grow but, as they become more able to fend for themselves, the number of flights will decrease until she eventually ceases feeding them. These increased levels of feeding usually last for approximately 55 days but this time her feeding flights lasted for 71 days, although it was noticed that in the latter stages of this mammoth 71-day effort her feeding flights had reduced in number, on average, to once a day.  As the eggs are laid, and therefore hatch, 2 to 3 days apart, she may have been feeding only one chick in the latter stages of the first nest, reducing the number of feeding flights as she tailed off her provision for her first brood, whilst also incubating her second one.

This second nest was extremely close to the path, something which would not have occurred had the path not been closed due to Covid19; giving lucky watchers at the Bittern Bus Stop, remarkable views of the female flying over their heads to look for food in the wildlife ponds; promoting plenty of oohs, and aahs, from the thrilled spectators.

Three young bittern were seen together from the second nest, and also a single bird on 2 occasions, with the female appearing to feed a youngster about a week later; meaning the female had produced between 7 -9 young within a season. What a tremendous achievement, she must have been exhausted.

We do not know if there were any more bittern nests on Old Moor or Bolton Ings, due to the lack of observing personnel due to Covid restrictions, but at least one other bittern appeared to be doing feeding flights, but nothing conclusive could be proved.

The year was rounded off in style with the appearance (if only briefly) of a magnificent male hen harrier, which was mobbed by a carrion crow.   Let us hope for more success in 2021. Lockdown has certainly had benefits for the wildlife on Old Moor, if not the personnel. “

Editor’s note: interestingly, in his piece, Gerald mentions that having marsh harriers breeding at RSPB Old Moor last year was a first for the Barnsley area. For the first recorded marsh harrier visiting the Barnsley area, see this copy of Mick Turton’s notebook from 2 August 1970 (yes, 1970!). Records show us that Marsh Harriers from then on where very infrequent visitors like the recordings suggest in the original Wath Ings Hide. (now loved and looked after as the Warden Teams bird monitoring and bird ringing hut):

Mick Turton 

  1974 Wath Ings Hide (Originalrecording 

Other Species:

Regular visitors to Old Moor will be familiar with many species that reside in the habitat besides the bittern and marsh harrier; so now is the time to introduce the beautiful avocet.

The avocet is unforgettable once seen in real life. Its graceful black and white physique is only surpassed by its delicate upturned bill. They use their bill to sweep across the water from side to side, or pick food from the water surface, or to dig into the sandy sediment below the surface. They eat small aquatic insects and small fish, and also feed on worms. 

These waders are around 42-45 cm in length (just a bit bigger than a woodpigeon), and have a wingspan of around 80 cm.  And if you look closely, they are not just a sleek black and white bird – they also have long blue legs.  And when you’re watching avocets, don’t be fooled by their “sleekness”, or their delicate appearance; during nesting and whilst raising chicks, the graceful avocet will be quite aggressive in the defence of their space and young; and nosy neighbours and would-be predators can get quite a rude awakening!

Avocets live in wetland areas, on beaches, in the marshes and mudflats, scrapes and estuaries.  Previously they had been driven to extinction in the UK, due to habitant disturbance, damage and pollution, and the behaviour of egg collectors. But the post-war flooding of coastal marshes to discourage German landings also created the perfect setting for the return of avocets. Now the UK has a breeding population of around 1500-2000 pairs, and up to 7500 birds in total.

Avocets can live up to 7 years, being able to breed after 2 years. They will often return year after year to the same breeding site, but will pair up only for the single season. Pairs build the nest together, on the scrape or muddy shore. They usually have 1 brood per year, laying 3 or 4 eggs, with an incubation period of 23-25 days; and both parents will incubate the eggs.  Chicks fledge after 35-42 days but will often stay near their parents for a while afterwards.

Avocet sketch                        Russ Boland

Avocet                                                                         G Lax

And if you think you have seen an avocet somewhere else, besides on the ings and scrapes in the Dearne Valley, you would be correct...

We will be showcasing another special species next time.

Recent sightings:

Old Moor: Ringed plover and little ringed plover, great white egret, kingfisher, bittern, common tern, wigeon.

Bullfinch, willow warbler, yellowhammer, blackcap, lesser whitethroat.


Kestrel, marsh harrier, sparrowhawk, buzzard, peregrine.

Great spotted woodpecker.

Common sandpiper, green sandpiper, black-tailed godwit, ruff, sanderling, dunlin, curlew, snipe.

Brimstone butterfly, comma butterfly, speckled bush cricket, common darter dragonflies.

Adwick: many of the above plus the amazing pectoral sandpiper.

Houghton and Edderthorpe: wood sandpiper and greenshank.

Other birds, flora and fauna to watch out for now in the Valley:

The month of August heralds the Autumn migration. When you are at Old Moor, Adwick or any of the other satellite sites, watch for the new seasonal arrivals. The water levels will be managed in line with Environmental Agency requirements; however, the sluices will be operating to ensure there are adequate scrapes for returning migrant waders.

Early Autumn is a great time for:

All manner of waders: common sandpiper, green sandpiper, redshank, spotted redshank, golden plover, little stint, curlew sandpiper.

Keep your eye out for young barn owls, learning the ropes as they hunt over the reedbeds.

Tons of insects: Red admiral butterflies, bees (like the red tail bumble bee) dragonflies (like the Emperor, Blue Tailed Damselfly, and Migrant Hawker), and shield bugs – look for the green ones -they are the most common species of shield bug - of up to 45 species in the UK!

Shield bug and young.      J Wilkinson                   Snipe                                G Lax

More on dragonflies can be found in Dave Pritchard’s series of fascinating blogs. I wonder if you knew that Damselflies have an eye on either side of a wide head, similar to a hammerhead shark. Dragonfly eyes wrap around the head and meet either in a point, or like a fighter pilot’s helmet.”?!!

To enter into the weird and wonderful world of dragonflies, follow the links below:

An Introduction

Its all about Wings

An Eye for an Eye

Whats in the Name? - The trouble with Hawkers

Blue tailed Damselfly in the Sensory Garden           D Pritchard

two Wool Carder Bees in the Sensory Garden   D Pritchard

 two Banded Demoiselles on the bank of the River Dearne    D Pritchard

Events and news to look out for :

 The Big Wild Summer

The 'Sting in the Trail' running throughout July

Learning all about THE most important insects - beeeeez

Going on a Bear Hunt running throughout August. A fun packed adventure trail for all the family.

Please refer to our Facebook Page for further details

Three Inch Fools presents Shakespeare like no other

RSPB Old Moor 18 September 7pm

20% Discount for Members - for further details and tickets Click here

“Lookout” for further wildlife updates and topics!        Please subscribe and comment

The new Lookout Hide   J Wilkinson