Summer 2020 - The perfect bittern year

2020 may be a year that many people would rather forget than remember but for one of our flagship reedbed species here on the Humber I thought it would be fitting to write a blog to mark what was simply the perfect year.

When I arrived to work here at Blacktoft way back in 1998, bittern was one of the of the species that I was asked to specifically manage the reedbed for and try and attract to breed. Indeed, it was at the time a priority UK bird species with less than 30 booming males and 20 nesting females recorded annually and had been lost from the Humber as a regular breeding species. 

Graph of UK bittern numbers 1990 - 2019

 

Not to help matters though I was then told that Blacktoft was probably unsuitable for bitterns as it was brackish (saltwater influence) and probably didn’t hold enough food. But then of course conservation is always about a challenge isn’t it? Never say never to someone from Yorkshire….

 At the time much of the British research had just started and there was a lot of hard work being undertaken by our RSPB bittern research team to investigate the then largely unknown ecology of the UK’s secretive breeding bitterns. But there were a few papers from other countries that looked at what was known, and one or two papers struck me profoundly when I read them, one was on the nesting ecology and habitat preference of the American bittern in the prairie potholes!

Have a read if you are interested

 https://pubs.usgs.gov/unnumbered/93890/report.pdf

What it did suggest was that the very similar American bittern would use all sorts of habitats and eat a wide variety of food, and coupled with an Italian paper that indicated the more available food there was during the breeding season the better success rate for nesting female bitterns.

And so, the team here at Blacktoft started to instigate the start of what has turned out to be a 20 year long journey of delivering more and better bittern habitat based on research data and observation.

 As said above one thing about Blacktoft is that we are estuarine and the water is brackish, this means that compared to sites like Lakenheath and Minsmere our food resource is very different. We don’t have Rudd or Roach or even perch, instead we have hundreds of thousands of sticklebacks that migrate into the site on tide. But we do have eels although not in great quantity, but then this may only be because of the eel’s massive declines? We also have low populations of frogs and newt, both a bittern favourite (I’ve never heard of them eating toads though and we have good numbers of these?)

 

The first success came in 2001 (foot and mouth year coincidentally) when the first booming and successful nesting was recorded which spurned us on to deliver more.

Following this we created new pools and amphibian ponds, ditches and sluices that would help the passage of migrant fish as much as is possible for a site that needs high surge tides to help bring food laden water into our lagoons. At the time we didn’t quite know what would work, but over the years we built up our knowledge by watching and learning.

Arial shot of habitat mosaic created for bittern

 

 It wasn’t until 2008 that there was another notable step change when amazingly we had two successful female bitterns breed on site, this is one of the females taken by one of our visitors and still one of my favourite shots of bittern.

 

This happy event allowed us to start to gather more and more information and with continued research information coming to the fore to inform us we started to gain a better insight into what the bitterns lacked on site. At this time, we also realised that in reality to make a real difference to this species, conservation needed to be on a landscape level. The bittern research team had already shown through radio tracking (in its very early days) that bittern was a very mobile species and could colonise new sites so creation of new reedbeds around the UK stood a great chance of colonisation if there were young birds looking for a territory of their own.

 In 2011 an opportunity for funding came about and we were successful in securing a grant for five years from WREN environmental, this was known as ‘Back to the Future’ , this innovative project really helped us put quite a few of our theories to the test. Here was one of the ambitious objective’s

Objective 4 says -Two pools will be dug in the reedbeds, measuring approximately 40m by 40m and 1 – 1.5m deep to provide food for bitterns nesting nearby. With outcome 1, this could help to increase the number of nesting females from 1-2 a year to 3-4. Increased breeding at Blacktoft will help to populate the wider Humber, the Humberhead Levels and beyond.

 This project also brought our Koniks to the reserve and allowed us to purchase the Softrack low ground pressure reed cutter, I still think to this day that the Back to the Future funding project has really made a dramatic step change in much of the conservation work on the reserve and around the site to improve the reedbed around the Singleton lagoon to benefit nesting bitterns.

Habitat created by mowing with the Softrak

 

As objective 4 says it aimed to create suitable habitat for nesting female bitterns, areas of wet reed that could provide safety and food. You can see below the initial stages created wet holes, some of which we planted up with reed some of which we left to reed over with time.

 

And another pond for comparison, we ended up creating 8+

 And now this is what they look like in 2020 – sometimes it takes a while for habitat to develop, conservation is often about vision rather than celebration!   

 

We took some reed rhizome over to Old Moor to create reedbed where as you know Bitterns have colonized and are amazingly doing very well! This area was a place I used to bird as a kid before Old Moor was created, as it was then Wath Ings.

 

And so, the scene was set for spring 2020 – lockdown! March had been preceded by one of the wettest winter periods ever on the reserve with a record 25+ surge tides, and this without me fully knowing at the time had set the scene of what was to follow. 

I'd suspected constant floods like this may have some benefits for some species but off course you never know 100% what benefits

It all started as always rather slowly in March with our regular booming bittern, one of the loudest I’ve ever known, this is a recording of his boom along with a sonogram. In terms of timing of boom though he wasn’t particularly early nor active as March was cool and dry.

You have to have a good sound system or earphones to hear these booms, crank up the sound to appreciate fully!

And then the soundwave (top) to show the intensity, male bitterns can be identified by their individual booms. The spectogram is a little less spectacular due to the double bass

 

But into April and suddenly as I went about my lockdown work I started noticing bitterns chasing each other around site, sometimes for quite a while! It started with two then three and one day while the three were chasing I had the feeling that there were birds flitting about the reedbed.

The chases were very intense 

 

 While this bird was very distinct with a deep chestnut collar, something I've never seen before. I didn't get a photo of this bird again or in fact didn't see it

 At this time of year though you really must be careful as there are still late Scandinavian birds around, and these can cause confusion when estimating breeding numbers. I once saw in late April two birds fly down river at Ousefleet which I thought were breeding birds, that is until they carried on flying on down river and over the Humber bridge!

But into May and it soon became apparent that something a little special was taking place. Off course we were still in lockdown but we were allowed with a limited team to do priority work, including monitoring and protecting our key species. But it was confusing to begin with, bitterns here, bittern there, bitterns everywhere! I’d never had this on site, every time you went to do work you saw a bittern, often flying but also increasingly walking along the edge of the lagoons and grazing marsh pools.

Video of bittern searching for food at Ousefleet where the koniks had been grazing

 To understand what was going on I took as many photo’s as I could to see if I could tell if the birds were male or female, it seemed that every one was a female! In fact, I never got a photo after April of a male!

 Some bird were a little more sneaky as they flew low over the reeds, male or female?!

This unique event required a bit more understanding, not only to get an idea of breeding females on site but to also understand the reasons behind this early season success and what habitat management and change in the ecology had taken place to have this going on.

The harriers and bitterns co-existed but didn't get on that well!

It did however require some serious time watching what was going on, often up to five hours of continuous observation often on my days off as there was so much other work to be done to cover for staff on furlough. But careful watching and diligent recording eventually allowed us to work out that it wasn’t two bittern nests, nor three, in fact there were four active bittern nests, something which came as a bit of a shock!

There was certainly some strange interactions!

 

 During the summer these glorious females foraged like mad to find food on site, the males don’t play any role in the upbringing of the young so the females really do have a challenging time to raise growing bittern chicks. In fact many studies show that it is starvation that is the main challenge for female bitterns often causing death of the chicks and predation in their weakened state. You can only imagine the volume of fish required to feed a brood of 3 – 4 chicks for 55 – 60 plus days.

 And so the females weaved their way around site, sometimes one after the other would drop into hot spots where there was food while at other times each would have their favourite place. I seem to recall that in about 4 hours one day I had 28 sightings as each bird fed roughly once every hour.

 

 Each time the information and observations built up a picture of what was happening and what the birds were feeding on and where they were nesting. The results were overall pretty amazing but also a positive affirmation that all the team’s efforts through delivering the aims of the Back to the Future project were all paying dividends.

Food wise it was pretty much sticklebacks and the odd glass eel that seemed to be the main prey items. Rather surprisingly the sticklebacks weren’t even adult size so in my reckoning some of the females must have been collecting 200+ prey items on each feeding trip alone!

Female collecting food

 

I’d been discussing some of the food availability with my contact Mike at the EA who is the local fisheries officer during lockdown by e-mail of course. He’d informed me that due to the wet year and large fresh water flows that had taken place there had been a massive first year fish fry recruitment into the fisheries, it seems this was driving bittern success all around the UK in 2020. But coupled with this there was also a massive influx of elvers into British riverine systems that were probably enticed up into the wetlands by wet conditions. This perfect ‘storm’ seemed to provide just at the right time a huge quantity of food to push the bitterns on to success.

You need an awful lot of these to feed a brood of bitterns

 

Elvers are small but packed with protein, I filmed a bittern catching one and slurp it up like spaghetti 

There were quite a few frogs this year, they make great bittern food

This fortunate surfeit of fish also coincided with the developing nesting and feeding habitat that we had created over the last few years, deep pools which were reeding over, new pools and ditches that were stuffed full of fry, sluices that allowed the passage of migrating sticklebacks and elvers and ran freshwater off site to attract them, konik grazed fen with shallow pools that provide early feeding opportunities and then a mosaic of reed ages to provide both feeding and nesting opportunities.

 This is one of our basic eel passes

Fish waiting to migrate into the lagoons at a sluice. Its all about numbers at Blacktoft!

 2020 for our breeding bitterns was truly memorable, all four nests on the reserve fledged young, with the most observable one yielding 3 healthy bitterns to go forth and colonise new sites. There was at least one other successful nest on a nearby site and then almost certainly another on land where we have helped the owner create bittern habitat. In fact, all the Humber sites had a momentous year all along the estuary, a credit to the efforts of partner organisations and their volunteers who have been seduced by this cryptic reedbed boomer.

Two of the young at the edge of the lagoon waiting for mum

 

And then all three chicks on a hot day trying to cool down

At times the chicks came a little closer - can you see them both?

I doubt 2021 will follow suit in regards success as things in conservation rarely do, however there is no doubt that Bittern is colonising in Ernst  both in Yorkshire and beyond, putting this once extinct species back into the UK’s reedbeds where it belongs. Truly an amazing story of landscape conservation of wetlands and an inspiration that when we all work together we can change things around.

So all the team here on the Humber are determined to do our bit where we can for 2021 to make this ethos work for a better environment, recovering bird populations and bringing more wildlife back to the estuary, whatever the world throws at us.