Les Cater
My Wildlife Images by Les Cater

Bittern Report

My thanks to all the people on the list below, who have contributed to this report/observation and have released personal and recorded data for me to use for my bittern study.

Philip Amies independent advisor and data collector

Dr Gillian Gilbert RSPB Scotland senior conservation scientist

Simon Wotton RSPB England Conservation scientist

Ben Andrew RSPB England wildlife advisor and photographer

Also, thanks to all who have helped me get this project off to an excellent start who are silently helping me in the background.


Introduction to my account of bittern behaviour I witnessed in April 2018 at RSPB Minsmere nature reserve.

Theses photos taken at the time by my self while under island mere hide reed beds, (which I later made a film strip of the existing photos) to show in an accurate possible real time account of the courtship-mating display.

Contributions, thoughts, assessment of that event and a collection of possibilities of the behaviour of these two bitterns by Philip amies, who in fact pointed out to me something I had not noticed, that in fact it could be two males in a mating courtship display.

His observations confirmed as a possibility of two males in a male-female courtship display by Gillian Gilbert and Simon Wooten who are leading experts on bittern behaviour for the RSPB.

I have added information from the web in following pages from bittern experts’ papers and reports used by myself and philip amies to try to establish a connection with my photos and past reports about male-male bittern behaviour.

This will be an ongoing chapter about Bittern behaviour with courtship-mating displays, which I have witnessed again in this year April 2024.
This time male-female and with clear evidence that they were in fact a male and a female, the earlier captured display back in April 2018 shows that the behaviour was as expected from a male to female, but in this earlier case, it looks like two males based on the beak lore colours and behaviour pattern that suggests in further photos that the reactions from first bittern towards second bittern, to be what you would expect from two males.

I am hoping to try to prove that it was in fact two males in the earlier account of April 2018, but it will be exceedingly difficult with certainty to prove this point. Nevertheless, I am hopeful to put together over time a collection of known and suspected behaviour reports from past collected data and papers from experts. This information will be of use in the future and be helpful for further investigations into bittern behaviour patterns.

Messages received from RSPB 29/01/24.

Hi Ben, one of these photos sent to me by Graham White, who saw it on Twitter! It does look like two males (in breeding condition) to me, a territorial dispute and older dominant male and a young male. The behaviour in DSC_8216 looks as though the bird could be reacting to an aerial predator? I have seen this behaviour when a Marsh Harrier has flown low over, for example. I have seen this behaviour between two males before, though very rarely when I was able to spend time surveying Bitterns in the field, this reported once or twice by others in the past by other Bittern surveyors elsewhere in the country.

Cheers Simon

Hi les, in our archive on RSPB Images we certainly do not have any images of Bitterns interacting in any way! Whether that be male-male or male-female or female-female!!

Such secretive birds!

Yep, I think these photos do have good scientific value for sure!

Got more Les, this time from Gillian,

Hi Ben and Simon, thanks for passing on great photos Ben - I had a wee look and I would be certain of the second bird being adult male, but the first bird I would edge towards a younger female, but with this not being certain. The iris colour of the first bird to land is light - which suggests a young bird, one fledged the previous year, but in order to be surer of age this would have to be combined with a look at the feathers for sign of moult and that would have to be in the autumn to be informative. The iris colour of the second bird is dark which is more definitive that this is an adult bird. The first bird has a greyish lore but the eye - ring is entirely without grey or blue colouration which sends me more in the female direction, but again to be definitive this would have to be confirmed with a weight and wing or tarsus measure to tell us this is a smaller bird and in the female size category. The second bird has blue going right around the eye which is more definitively male. Interesting to see the second bird fluff out his white shoulder patches.

I would have expected the other bird to do the same if they had both been males and if they had antagonistic or territorial intentions, which I have seen from territorial males squaring up to each other. If the first bird had been a young male, then following the older male is risky behaviour. We do know from radio tracking that young males in their first breeding season that are not booming will hang about in the territories of older booming males, and we supposed this was so that the younger males might opportunistically mate with females nesting in the older male’s territory. However, our knowledge of this came from tagged birds that were always out of sight hidden in the reedbed and I would have thought this sneaky behaviour would have happened out of sight. Males in the breeding season can be quite aggressive, even to females when they come up from the nest to find food, we sometimes saw these females relentlessly chased and forced down into the reedbed again by males. Excuse the long-winded answer! Best wishes, Gillian

A further e-mail from Gillian!

Hi Simon, the bird in photo 8216 is the one I was calling the first bird, and it has a lighter eye and a hint of blue/grey at the base of the bill but no blue around the eye like the other bird. Possibly that smaller, younger bird is a male - but it is equally possibly a female. The best photo I thought for comparison was the 8370 one. Ben, you have got us going with this one! All the best, Gillian.

Comments, observations and records below provided by Philip Amies.

This paper is using plumage details to sex Bitterns which is unused these days. The paper I sent you the other day is current idea that the blue lores separates male in breeding season.

Bird Study Paper

James McCallum has read your account which he says fits with his experience of two males disagreeing something he has seen a few times, he has not seen copulation, seems few have and can find no photos of it on google image search.

Gary Hibberd Holme warden found your account interesting.

So far four people have said they think a disagreement between two males is the best explanation, which is my opinion, blue lores shown by both birds seen as evidence of two males, and behaviour fits with conflict between two males.

A group of commentators have seen this before (I have seen male disagreements) and everybody thinks it is interesting, behaviour is always difficult to be certain about, attempted mounting might be conflict not prelude to copulation. I am awaiting some more comments and people I have forwarded account to are sharing it.


I have not seen courtship, neither has James, or Gary or at least the result copulation. Reading account of Italian paper is interesting, given they were sexing by size and plumage colour they could be describing both courtship and male - male conflict, but they do describe what seems to be copulation (cloaca of female in contact with male cloaca which requires some twisting on the part of the female bird which is the key thing to see when a bird mount another).

Their sexing is based on plumage and size, now the method used today is colour of lores in breeding season (male blue), so they do not record that making it a less useful account. I will look for others.

It really does show how little is known about bittern behaviour and there is still more to discover in the future. Yes, as you say shame Greylag flew in at that time and disturbed them. From the Italian ornithologist’s description male keeping his neck extended and bill pointing downwards, (sadly they do not say if neck feathers puffed out or flat, but perhaps they would be more likely to mention puffed out) walked alongside (first right side, then left side side) female who had her body parallel with the ground, neck and bill pointing skywards.

I think this is interesting, the female with her body parallel to the ground, neck and bill pointing up would seem to be inviting copulation, male with bill pointing downwards could be said to be showing he was no threat, not an aggressive posture, books often mention how copulation for solitary birds needs display which shows it is safe to allow contact.

Just trying to find an account by Bert Axell of Minsmere fame of aerial chase male following female resulted in male forcing female down and copulating, two other older authors recorded same.

It is interesting, with behaviour we must be cautious, have an open mind especially with such secretive birds as there is little known about this behaviour. I am enjoying learning more reading and getting peoples comments.

The differences in behaviour may be subtle, exact posture, degree of neck feathers fluffed out, I'm sure the Bitterns now exactly what is happening, but we might not be aware of how to us a small posture difference or degree of feather puffing, or timing of events might mean what looks rather similar is very different behaviour for Bitterns.

Interesting, I don't recall seeing such a full set of images such as yours, it was prolonged not a brief fight, shows wing spreading into deltoid shape, fluffed out neck feathers, also how lulls can occur with preening often in past described as distraction activity, although one of the birds was bigger it suggests maybe both not fighting to point either get hurt, maybe a process of challenge with an element of tolerance/backing down. It makes sense to have a mechanism to develop a 'pecking order' in a stylised way, they could hurt each other badly which is not a gain for either. I'd suspect males end up knowing each other.


DSC 8338

This is interesting Bert Axell speculates did he see copulation, or a male mounting a male with two other males flying above 'pair.

I have not seen much here locally where I live, as we do not have enough birds here. Friends have seen bitterns chasing other bitterns on the Somerset Levels, it is also frequently seen at Lakenheath. Worth searching out references to old papers.

The open wing display of one of your birds with puffed out neck feathers could be an aggressive behaviour towards another male.

This paper published in 2003, so not using the sex identification such as male blue lores in the paper I sent link to previous document which was published in 2007.
I will find the reference for the Axell British Birds paper and let you have it.


Methods still used today to recognise the difference between a male and female Bitterns.

On the ground or in flight, you would look for size differences between the male and female, it is known that the male will be larger than the female.

In flight, you will be able to see the difference much easier than on the ground, especially if you have two bitterns in a chase you can then see the size difference, it's likely it is a male which is larger will be the one chasing the female that is smaller. But, in some cases that might be more difficult to see, if both birds are females or both males, then size difference is not clear, and if you can get a clear view of the beak colour, then that will help you to seperate the males from the females. More examples in photo evidence will be presented.

Recently I had a male chasing a female in flight that lasted for over twenty-three minutes, this was a record for me personally which was amazing to witness. The interesting part about this observation was, the female gained more hight about twenty minutes into that flight, as she regurgitated her food or was stressed enough that she out of purs exhaustion was sicking up her food. Either way it worked, she shortly after that managed to get higher and the mail gave up chasing her, they finally both landed a good distance apart in the reed beds exhausted.

Sometimes you will get more than one bittern in flight, and I have had up to five bitterns chasing each other in an aggressive way, and you would assume it is more than one male chasing a female, on the other hand it could be a mix of males and females.

There have been accounts of one male chasing down four females into the reed beds, forcing them down so he could mate with them all, as described by Bert Axle and Eric Hosking in their book, Minsmere Portrait of a Bird Reserve published in 1977. Here Bert axle describes an occasion of such sightings right in front of his eyes while he was in the reed beds recording bittern nest’s locations.

So, it is down to seeing the bittern’s size (if possible) to ascertain the sex of the bittern, and there is some information regarding bitterns’ size which cannot be physically be measured. So, some male bitterns sometimes do not grow to full size, or it is a juvenile bittern, but it is possible to have a smaller male in this species, due to growth problems or genetic background interference.

Overall, there is room for discussion in what you see before you, may not always be what it seems.

There is another method that is a standard definition used by most experts as a basis to identify a male from a female. This is the lore, or colour patch on the upper part of the beak where it extends from the head near the eye socket. The males develop a bright powdered blue/grey patch that will as the male matures extend around the eye socket as a small outer ring and the upper beak area near the head during breeding season.

Females will have a greenish/yellow colour lore on the upper part of the beak and again the colour will extend all the way round the eye socket also like an outer ring around the eye. Sometimes, in different light it can look grey on females, and that leads to confusion it might be a male because of this. But there is another helpful piece of observation here that can help, females have bright orange/yellow eyes, the males tend to have a darker red eye, a blood red colour sometimes in other males.

Putting these helpful observations together, will allow you to clearly see the difference between a male and a female, but you will need to get a closer look at the eyes and beak area to do so.

Even though with this information you can say with certainty the difference between a male and a female, you need to be sure not just by size difference, but also with the markings around the beak and eye area there still can be a possibility that what looks to be a male might not be the case in some circumstances.  

I have a series of photos taken by myself of a bittern that has a partly formed blue lore on the upper beak, but the blue colour does not entirely go all the way around the eye socket as a blue ring that is still green and the eye is orange.

Here begins the interesting part of my observations and the event that happened that April evening back in 2018 when two bitterns engaged in a mating courtship display and resulted in one bittern the male trying to mount the other bittern a suspected female, it was noted by philip amies who had seen the photos on social media page, that the second submissive bittern was possibly another younger male.