Category Archives: Biodiversity

Is Biodiversity Net Gain a missed opportunity for invertebrate conservation? A new open access study suggest ways to improve it

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The UK has set ambitious targets under the Global Biodiversity Framework 2030, aiming to halt and reverse biodiversity loss. One of the key policies designed to help achieve this is Biodiversity Net Gain (BNG), a requirement in England that ensures new developments (such as housing projects) result in a 10% increase in biodiversity. On the surface, this sounds like a positive step—but is it really working for all species?

In a newly published paper that I co-authored, led by University of Oxford PhD student Natalie Duffus, we suggest that BNG may be falling short for some of the most vital, yet overlooked, members of our ecosystems: invertebrates. This group includes insects, spiders, and other arthropods—organisms that play critical roles in pollination, pest control, and nutrient cycling but are also experiencing dramatic population declines worldwide.

The Problem with a Habitat-Focused Approach

The way BNG is currently applied focuses heavily on habitats rather than species, meaning that while new green spaces may be created, they may not necessarily provide the right conditions for invertebrates to thrive. In some cases, BNG could even make things worse by fragmenting existing habitats or failing to account for the complex ecological needs of different species.

For instance, many invertebrates rely on very specific plants, soil conditions, and microhabitats that a broad-brush approach to habitat restoration may not support. Simply increasing the area of green space does not guarantee it will be suitable for pollinators, decomposers, or predatory insects that help keep ecosystems functioning. It’s an issue that I highlighted in October 2023 when I wrote a report about BNG and pollinators.

How Can BNG Be Improved?

Rather than being a one-size-fits-all approach, BNG could be better aligned with evidence-based conservation strategies, such as the National Pollinator Strategy. By integrating more targeted actions—including planting native wildflowers, preserving deadwood for beetles, or ensuring hedgerows and wetlands remain intact—BNG could deliver real benefits for invertebrates.

Additionally, better monitoring and evaluation are needed to track whether biodiversity is genuinely improving under BNG policies. This would help policymakers refine their approach and ensure conservation efforts support the widest possible range of species, not just the most obvious or easily monitored ones.

Lessons for Global Conservation

With many countries looking to adopt biodiversity offsetting schemes like BNG, England’s experience offers valuable lessons. If BNG is to be truly effective, it must take a more holistic, species-specific approach—one that recognizes the essential role of invertebrates and actively works to protect and enhance their populations.

If done right, BNG could be a game-changer for conservation. But if we fail to consider the full picture, it risks becoming a well-intentioned policy that does little to halt biodiversity loss where it matters most.

Here’s the full reference with a link to the paper – it’s open access and can be downloaded for free:

Duffus, N.E., Lewis, O.T., Grenyer, R., Comont, R.F., Goddard., D., Goulson, D., Ollerton, J., Townsend, M.C., Webb, J.A., Wilson, R.I. & zu Ermgassen, S.O.S.E. (2025) Leveraging Biodiversity Net Gain to address invertebrate declines in England. Insect Conservation and Diversity (in press)

Is Common Elder an under-appreciated habitat for bats? [updated]

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Regular readers of my blog may recall that I have an obsession with something of an interest in Common Elder (Sambucus nigra) that goes back to my childhood, as I recounted in an article for British Wildlife back in 2022. In that article I mentioned that the larger hollow trunks and branches of elder “can offer nesting opportunities for birds and small mammals”, but didn’t go into detail. The mammals I was thinking of at the time were small rodents, but following a long country walk with Karin recently I wondered whether bats might also make use of these hollows as roosts for breeding and/or hibernation.

I posed this as a question for the bat specialists in the British Ecologists Facebook Group and received several replies, with respondents mentioning that they had encountered Natterer’s Bat (Myotis nattereri), Common Pipistrelles (Pipistrellus pipistrellus), and Brown Long-eared Bat (Plecotus auritus), in hollow elder trees, during summer and autumn surveys.

A couple of people suggested that I check out Arbology’s Look-up Tool for the Bat Tree Habitat Key (BTHK) database which records trees that are used by bats, but to my surprise it returned the following message:

“There are no positive results which match your query.
This does not mean that bats won’t use the feature type in the species and habitat you have selected, but current data suggests that survey effort may be better focused on features which have a proven occupation”. 

The BTHK relies on bat surveyors adding their observations, but clearly no one has submitted records of bats in elder, despite the fact that we know they occur. This concerns me for two reasons.

Firstly, of all of our smaller native woodland edge and hedgerow trees, elder is (in my experience) the one most likely to have significant cavities in their trunks and branches. The specialists in the Facebook Group introduced me to the phrase “if they fit, they sit”, meaning that almost any cavity might contain bats, even quite low to the ground: one respondent mentioned that a friend had found two Common Pipistrelles during an autumn survey, in a dead elder stem less than ten centimeters in diameter at about one metre above ground level.

Secondly, it’s not unusual for old elder trees to be cut right to the ground or even removed completely during work on hedgerows. It’s a neglected, even despised native British tree that, as I noted in that British Wildlife article, is:

“generally considered by naturalists, when it is considered at all, as rather boring, so commonplace that we hardly give it a second glance…[and by some as]…’barely a tree at all, more of a weed'”

Another respondent mentioned that ​tubular structures, such as elder branches, are less likely to be identified as active bat roosts in the absence of bats, as they provide limited shelter and often lack droppings, which tend to fall out, leaving minimal evidence. I’m sure that’s not the whole story, however, I think it’s more likely that small trees generally are overlooked when it comes to habitat for bats: the BTHK has a single entry for Common Hawthorn (Crataegus monogyna) and nothing for Blackthorn (Prunus spinosa), for instance.

In addition to bats, another respondent noted that Willow Tits (Poecile montanus), a species experiencing significant decline and now red-listed in the UK, often nest in elder trunks, where they excavate cavities in decaying wood. That’s yet another reason why we should pay more attention to this most interesting of trees!

My thanks to all of the British Ecologists who replied to my query. As always, feel free to comment or get in touch via my Contact page.

UPDATE: After I posted this on Bluesky, Richard Broughton, author of The Marsh Tit and the Willow Tit, pointed out that elder is also a significant nesting site for Marsh Tits (Poecile palustris), another red-listed species. To quote Richard’s comment:

“Elder is prob[ably] the very best cavity-bearing shrub, far better than hawthorn, hazel, blackthorn (very poor). Important nesting shrub for Marsh Tits & Willow Tits, but only if left to develop old trunks and cavities, not cut. Like Hazel, they self-coppice without management, with new growth from base….in Wytham Marsh Tit studies Elder was the main nest tree/shrub. Though it’s not common/available in woods everywhere. It develops *really* good hollow nest cavities for the small hole-nesting guild, and also very amenable for Willow Tits to excavate. Prob[ably] important in hedges, where holes rare.”

Richard kindly shared a scan from his book showing that for Willow Tits, elder ranks second (after willow and birch) and for Marsh Tits it ranks second after Ash.

Evolutionary implications of a deep-time perspective on insect pollination – a new review just published

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When we think of pollination, we often picture bees buzzing around flowers or butterflies flitting from bloom to bloom. This relationship between plants and pollinators is one of the most well-known interactions in nature. But insect pollination didn’t begin with the colorful flowers we see today. In fact, pollinators were at work millions of years before flowering plants (angiosperms) even existed. In a new review led by Spanish researchers David Peris and Ricardo Pérez-de la Fuente, to which I added a modern ecological perspective, we explored this topic and why it’s relevant to our current understanding of plant-pollinator relationships.

Despite centuries of research on pollination, the fossil record of pollinating insects has only gained serious attention in the past few decades. What palaeontologists have uncovered is reshaping our understanding of pollination’s origins. It turns out that insects were pollinating plants long before flowers evolved—playing a crucial role in the reproduction of ancient gymnosperms, the group of seed-producing plants that includes conifers, cycads, and ginkgos.

Most people assume that insect pollination began with flowering plants, but the evidence tells a different story. Fossilised insects with specialised body structures for carrying pollen—such as hairy bodies or mouthparts adapted for nectar-feeding—have been found in deposits dating back hundreds of millions of years. These early pollinators likely visited gymnosperms, helping them reproduce in a world that looked vastly different from today’s landscapes.

Ancient pollination was driven by a diverse range of insects, many of which are now extinct. The fossil record reveals that various insect groups—including beetles, flies, wasps, and even some long-lost relatives of modern lacewings—were already acting as pollinators long before the first flower bloomed. This means that pollination as an ecological process has far deeper evolutionary roots than many realise.

As plants evolved, so did their pollinators. The rise of flowering plants during the Cretaceous period (around 100 million years ago) transformed pollination systems, leading to the incredible diversity of plant-pollinator relationships we see today. Many of the insect groups that once dominated pollination in prehistoric times have since declined or disappeared, replaced by the bees, butterflies, and other familiar pollinators that thrive in modern ecosystems.

Understanding this long history is essential—not just for scientists, but for anyone interested in biodiversity and conservation. When we focus only on present-day pollinators and plants, we miss a crucial part of the story. The fossil record helps us see how pollination has changed over time, which in turn can offer insights into how today’s ecosystems might respond to environmental pressures such as climate change and habitat loss.

Recognising the ancient history of insect pollination isn’t just an academic exercise—it has real-world implications. If we understand how pollination evolved and adapted to past environmental changes, we can better predict how it might shift in the future. Conservation efforts that aim to protect pollinators today can benefit from a long-term perspective, ensuring that we’re not just responding to recent trends but also considering deep-time ecological processes.

So the next time you see a bee visiting a flower, remember—you’re witnessing the latest chapter in a story that began hundreds of millions of years ago. The relationship between plants and pollinators is far older, more complex, and more fascinating than we ever imagined.

Here’s the reference with a link to the paper. It should be open access, but if you have problems obtaining it, send me a message via my Contact page:

Peris, D., Ollerton, J., Sauquet, H., Hidalgo, O., Peñalver, E., Magrach, A., Álvarez-Parra, S., Peña-Kairath, C., Condamine, F.L., Delclòs, X. & Pérez-de la Fuente, R. (2025) Evolutionary implications of a deep-time perspective on insect pollination. Biological Reviews (in press)

What is happening to wild bees in Britain?

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Recently the Bumblebee Conservation Trust (BCT) reported that, in 2024, British bumblebees experienced their worst year since the BCT started its monitoring campaign. Overall, the numbers of bees were down by more than one fifth, with one of our commonest species, the Red-tailed Bumblebee (Bombus lapidarius) declining a staggering 74%! The cause seems to be the cold, wet spring of 2024 and we have to hope that this is a blip that will not be repeated in 2025. So far the year has been cold and I didn’t see my first queen bumblebee flying until early March. But the very warm weather over the last few days has encouraged bumblebees out of hibernation and plants to start flowering.

Long-term monitoring of the type that the BCT undertakes with its volunteers, is vital if we are to understand how British pollinators are faring. When I compiled the evidence for the chapter entitled ‘The shifting fates of pollinators’ in my book Pollinators & Pollination: Nature and Society, I tried to give a global overview, but also focused on British records, which are probably the best long-term data that is available on trends in pollinators. This information is compiled by the Joint Nature Conservation Committee (JNCC) as part of its annual UK Biodiversity Indicators reports. Each year it produces an indicator showing trends in bees, hoverflies, and the two combined as an overall pollinator trend*. To quote the JNCC website:

The indicator is based on 394 species (158 species of bee and 236 species of hoverfly), and measures change in the number of 1 kilometre grid squares across the UK in which they were recorded in any given year: this is referred to as the ‘occupancy index’.

The bee data comes from the Bees, Wasps and Ants Recording Society (BWARS) and the graph of bee trends that I used in that chapter of my book assessed records up until 2017. It looked like this:

As you can see, the index fluctuated a bit but was on average fairly stable up until 2005, after which there was a sharp decline, then an uptick from about 2014, though still low compared to the 1980 baseline. The overall impression is that bees had a tough time from the early 2000s onward, but things seem to be improving.

Since my book came out in 2021 I’ve given a lot of talks to natural history societies, ran training with consultancies and local councils, and so forth. Each year I update the JNCC graphs in my talks to give the audience the latest information. This is the one I used last year, which took the data up to 2019**:

This looks a bit different – the fluctuations are more pronounced – but overall the trend is similar, though the drop after 2015 is worrying. The impression is that there’s been big (cyclical?) fluctuations in the bee index over time, but its generally always below the 1980 baseline.

Updating the story to 2022 (the most recent available) shows a very different picture:

The impression it gives is that there’s been some modest fluctuations in the bee index, but then from about 2013 onward, the index has massively improved and now wild bees are doing better than ever!

What’s happening here? Why are these three graphs – published over a period of about five years – giving such different impressions of what’s happening to wild bees in Britain? As far as I can tell there’s two main reasons for the changes. The first is that the number of bee species included in the index increased from 137 to 148 to 158. Adding species for which there was previously no or little data is clearly going to have an effect.

The second reason, perhaps more fundamental, is that the method used for calculating the index has been refined, as explained in the technical annex to the study. That’s important because the data underlying the bee index was never collected in a standardised way for the purposes of assessing species’ trends. For this reason the UK Pollinator Monitoring Scheme (PoMS) was developed and it’s interesting to see that the data in the latest PoMS report shows some stability in wild bee abundance from 2017 to 2022:

So the latest data suggests that, for once, there’s some good news in the world of British wildlife. Does this mean that we should be complacent about the state of our wild bees? Absolutely not! As always, the devil’s in the details. The BCT report that I cited at the start of this post provides one level of (worrying) detail. But another is provided by the JNCC’s own statistics. As well as showing the overall trend in the bee index, the analysis digs into what is happening for individual species and provides a helpful summary figure like this:

Clearly many species are doing well, or at least have not changed since the 1980s. But more than one quarter of British wild bees are showing a weak or strong decline over the long term. That’s a clear signal that we need to keep on with our efforts to support wildlife and enhance our strategies to improve the state of nature in Britain.

As always, feel free to comment on the post or get in touch via my Contact page.

My sincere thanks to all of the volunteer naturalists who collect the data used by JNCC and PoMS – the task of assessing trends in wildlife would be impossible without your commitment!

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*Why JNCC does not include butterflies – which are assessed separately – in this overall trend is unclear to me, as we know that they can be important pollinators for some plants – see my blog post: ‘Butterflies, bumblebees and hoverflies can be equally effective pollinators of some plants says a new study‘.

**The data in the JNCC report is always a couple of years behind the publication date.

Join me for a talk at Northamptonshire Bird Club – Wednesday 5th March

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The first in a series of public talks that I’m doing this year to promote my book Birds & Flowers: An Intimate 50 Million Year Relationship will take place at Northamptonshire Bird Club on Wednesday 5th March at 19:30.

If you follow this link you can find out more details of the talk and venue.

I’m happy to consider giving similar talks to bird groups across the country, either in person or online. Please use my Contact page to get in touch.

How urban spaces support pollinators – a new study just published

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Bees play a vital role in pollination, supporting both natural ecosystems and our food supply. However, their numbers are declining globally due to multiple threats—including urbanisation. As cities expand, understanding how different habitats within urban areas affect pollinator populations is crucial for conservation efforts and for supporting urban and peri-urban agriculture. It’s a topic to which I devoted whole chapters in my books Pollinators & Pollination: Nature and Society and Birds & Flowers: An Intimate 50 Million Year Relationship.

The latest paper from Muzafar Sirohi‘s PhD thesis has just been published in the journal Urban Ecosystems. It follows on from his two other recent papers on plant–bee interactions and resource utilisation and how the timing of emergence of solitary bees varies between urban and non-urban settings.

This element of Muzafar’s work explored how solitary and primitively eusocial bees (those that live alone or in simple social groups) respond to different aspects of city landscapes. He examined local habitat factors such as floral diversity, bare soil availability, and sunlight exposure, alongside broader urban features like green spaces, roads, and paved areas.

The findings highlight that small-scale habitat conditions—especially the variety of flowering plants and access to sunlight—had a greater influence on bee diversity and abundance than overall habitat size. While larger landscape features, such as urban green spaces, played a role at a broader scale, even small patches of wild vegetation and roadsides were found to be important for bees.

These results challenge the idea that bees need large, uninterrupted green spaces to thrive. Instead, even fragmented urban habitats, when managed thoughtfully, can support pollinators. By planting diverse flowers, preserving patches of wild vegetation, and maintaining sunlit areas, cities can become havens for these essential insects.

Simple changes—like creating wildflower-rich roadside verges or maintaining natural pockets of greenery—can make a significant difference. As urbanisation continues, ensuring that bees have the resources they need to survive will be key to supporting biodiversity and maintaining the critical pollination services they provide.

Here’s the reference with a link to the published study; if you are not able to access it, send me a request for a PDF via my Contact page:

Sirohi, M.H., Jackson, J. & Ollerton, J. (2025) Influence of urban land cover and habitat quality on wild bees. Urban Ecosystems 28:78 – https://doi.org/10.1007/s11252-025-01687-6

Here’s the abstract:

Solitary and primitively eusocial bees are important pollinators of plants, which are experiencing a global decline. Urbanisation is one of the contributing factors to this decline. It is crucial to understand the complex community dynamics of solitary and primitively eusocial bees in urban areas as urbanization grows globally. For bee communities, the local habitat as well as the surrounding urban landscape play an important role. The study considered four local habitat variables: habitat size, floral species richness, bare soil and shade. Moreover, five common land cover types (green space, buildings, roads, car parks, and paved surfaces) were assessed at multiple spatial scales from 40 m to 200 m from the centre of the sites with 20 m steps, analysing their potential impacts on the bee community. The study found a greater effect of local habitat compared to landscape variables at a smaller spatial scale. However, landscapes affected the bee community at larger spatial scales. The size of the habitat did not affect the bee community in urban areas. However, habitats with a higher number of plant species and exposed to sunlight attracted relatively more bees. This study suggests that urban areas are capable of conserving solitary and primitively eusocial bees. Although green space is important for the dispersal of species at larger landscape scales, small patches of wild, leftover vegetation and roadsides are equally important for bees. The management of bee friendly open vegetation with wildflowers would be beneficial for the successful conservation of solitary and primitively eusocial bees in urban areas.

No, the HS2 ‘bat tunnel’ has not cost £300,000 per bat

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As I write I’m listening to the Radio 4 series AntiSocial with Adam Fleming and this week the topic is the economic and social cost of nature conservation. One of the topics being discussed is the so-called ‘bat tunnel’ being built through an area of ancient woodland in Buckinghamshire. The cost has been estimated at £100 million and, according to The Times, this amounts to £300,000 per bat protected. That’s clearly a lot of money to protect bats, but is it an accurate reflection of reality? The answer is no, and here’s why.

Let’s put aside the fact that the ‘bat tunnel’ will protect a lot of other wildlife associated with this area of ancient woodland, including other bat species and a range of additional mammals, birds and insects. Let’s also ignore the fact that the cost of the tunnel is so high because of decisions made by HS2 that have nothing to do with bats, such as making it wider to accommodate local train services. Let’s instead just focus on the type of bat that’s being specifically discussed, Bechstein’s bat. It is indeed a rare bat in Britain, known from just six breeding populations, all associated with ancient woodland (itself a rare habitat type in this country).

The population that the ‘bat tunnel’ protects is estimated to be 300 individuals – that’s where the figure of £300,000 per bat comes from, i.e. £100 million divided by 300 (actually £333,333 per bat, but let’s not quibble about a few tens of thousands of pounds when HS2 is going to cost tens of billions).

Anyone in possession of both a sense of proportion and some basic maths can see that such a calculation is nonsense. The tunnel will be in place for many decades, potentially hundreds of years. Over time bats will die and other bats will be born. Some will stay in the area and others will migrate away and (hopefully) found other populations, or at least add to the genetic diversity and growth of one of the other existing populations. Calculating the cost-per-bat on this basis is both impossible and nonsensical. But then making that initial calculation was also a pointless exercise. The only reason to do it was to generate publicity and clicks for a newspaper that ought to know better.

As I’ve previously discussed, the railway system of Britain and the rest of Europe has both a negative and a positive impact on biodiversity across the region, and understanding those impacts is important. Thoughtless, politically-motivated journalism such as The Times is promoting is not helpful.

(Before anyone asks, the photograph accompanying this post does NOT show the ‘bat tunnel’! It’s a tunnel in Tenerife, part of the network of water conduits that were built in the past and now provide homes for many of the resident bats)

Was this the first online database of plant-pollinator interactions?

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Over the past few years, the ways in which we collate and use large databases of plant-pollinator interactions, and make them publicly available according to FAIR data principles, has been much on my mind. These were and are important considerations for several projects, including the Pollinators of Apocynaceae Database; the pandemic garden pollinators initiative that I coordinated during lock-down; the WorldFAIR project; and, most recently, an EU-funded project called BUTTERFLY that launches in April and involves both the DoPI and GloBI databases.

The latter are just two of a growing number of databases making information about plant-pollinator interactions in wild and agricultural settings freely available to other scientists and to wider stakeholders. An intriguing question to those of us interested in the history of pollination ecology as a science is: what was the first such online database? I think that I have the answer, but I’m happy to be corrected. But first some background.

Since returning to Britain from Denmark in March, Karin and I have been renting a house from some friends as a temporary measure before we found somewhere else to live. A really nice property became available late last year and we decided to move in on 18th December. Then last week the final consignment of boxes and furniture that we’d had in storage arrived at our new home and we’ve been spending time deciding what we want to keep and what needs disposing of.

I’d be the first to admit that I’ve always been something of a hoarder when it comes to books and paperwork, so one of my priorities has been thinning out the contents of old folders and box files. Yesterday I opened one that contained a sheaf of papers related to the study that Sigrid Liede-Schumann and I published on pollination systems in the family Asclepiadaceae (now subsumed into Apocynaceae). One of the items I found is, I think, a fascinating piece of history with regard to online interaction databases.

As you can see in the image above, it’s a print-out* of an email that I received on 31st December 1995 from Mark Fishbein. If I recall correctly, I’d met Mark at a conference and he’d mentioned that he’d been compiling published and unpublished records of pollinators of North American Asclepiadaceae into a database. In this email he tells me that:

“I now have my data base accessible (primitively) on the World Wide Web. It would be easiest for me if you accessed the data base this way…Here’s what to do (if you have access to a web browser)…”

As we complete the first quarter of the 21st century it’s difficult to conceive that, less than 30 years ago, people were saying things like “if you have access to a web browser”! But the World Wide Web was only opened to public use in 1991 and even by the mid-90s, was not being widely used even in academia. Note also that Mark’s database was not password protected – it was freely (FAIRly?) available to anyone who could access it. In this regard Mark was certainly ahead of his time and, as far as I know, “pollrec” was the first online database of plant-pollinator interactions.

After we published our paper in 1997, Sigrid and I made what was then termed ASCLEPOL (including Mark’s and our own records) available online, and this was later merged with APOPOL to form the basis of the Pollinators of Apocynaceae Database. The latter is not formally available online, but it is available as supplementary information in the paper and has been merged into GloBI.

Thirty years is not a long time in real terms, but over that period there’s been huge cultural changes as far as society is concerned, and we take for granted things like online access to information that were hardly conceived of back then. But in 1995, Mark’s approach was revolutionary, even if we didn’t appreciate it at the time. When I emailed him about it yesterday he told me that he was “comfortable with my new role of being someone of historical interest”, followed by a smiley face emoji (another late 20th century development). So thank you Mark, this blog post is for you!

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*Yes kids, back in the day grandpa printed out some important emails so as not to lose them.

Join me for two talks next week: South Leicester Birdwatchers (in person) and the Countryside Regeneration Trust (online)

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It’s been a busy year for talks! But next week sees the final two of 2024 put to bed:

On Tuesday 12th November at 6.45pm I’ll be speaking in person about my recent book Birds & Flowers: An Intimate 50 Million Year Relationship at South Leicester Birdwatchers – details can be found by following this link. I’ll bring along copies of my books to buy – the perfect Christmas gift!

On Thursday 14th November at 7pm I’ll be giving an online presentation to the Countryside Regeneration Trust about UK pollinators and how farmers and other large landowners can help to conserve their populations – booking details are here.

I hope to see you at one or both of these talks.