I was recently reminded in conversation of a topic in biology that I find fascinating, not only due to the sometimes described ‘paradoxical’ evolutionary nature of its existence, but also due to the potential biases that have surrounded its study for centuries.
 
Across the vast diversity of the animal kingdom, one behaviour has often baffled biologists: same-sex sexual behaviour. This is not the same as a homosexual orientation in humans, which more closely aligns with what is referred to as same-sex sexual preference (i.e. when individuals are more likely to undergo sexual behaviour with individuals of the same sex as themselves when different-sex partners are available). From penguins to primates, and even insects, same-sex sexual behaviour is common across species (for a great book on this, see Joan Roughgarden’s “Evolution’s Rainbow”, or Bailey and Zuk’s shorter review paper). But why would animals invest in behaviours that don't directly lead to reproduction? Isn’t that an evolutionary dead-end? This question has sparked many studies, arguments and controversy among the research community, with scientists traditionally framing same-sex sexual behaviour as an evolutionary costly behaviour that begs for an adaptive explanation. An alternative perspective, however, turns this idea on its head: the "ancestral indiscriminate sexual behaviour" hypothesis.
 
This challenges the notion that animals evolved from ancestors engaging exclusively in different-sex sexual behaviour, from which same-sex sexual behaviour has evolved. Instead, it suggests that the earliest sexual behaviours weren’t sex-specific at all, but animals directed their mating efforts at whoever was available, regardless of sex. Could this ancestral state explain the persistence of same-sex sexual behaviour in the animal kingdom today?
 
To understand this, we must imagine the world’s first sexually-reproducing animals. These were different to the complex multicellular animals that we are used to seeing on our TV screens today, with nature documentaries often showcasing male animals jostling it out to impress the females and attain mating opportunities. Long before elaborate courtship rituals emerged, these ancestral species didn’t have the ability to finely-tune mate recognition. Instead, we must picture a much simpler organism, consisting of just one cell. Billions of years ago, these single cells began to swap, shuffle and merge their DNA with one another, creating new cells with unique genetic combinations. While it may not resemble the intricate processes we see today, this was the humble beginning of sexual reproduction and behaviour.
 
Sexual reproduction gave organisms an edge over asexual ones by mixing genetic material, allowing offspring to adapt better to changing environments compared to clones produced through asexual reproduction. As is often the case in evolution, this new method of reproduction sparked competition between individuals, where some cells wanted to become smaller and more mobile to increase their chances of fertilising others. Because these smaller cells contributed fewer resources to new offspring, it became necessary for other cells to evolve to become larger and more nutrient-rich, so that new and developing offspring had enough energy to survive. It was this evolutionary race for reproduction that ultimately led to the evolution of biological sex, where two distinct sex cells (called gametes) evolved: male sperm and female eggs.
 
The crux of the ancestral indiscriminate sexual behaviour hypothesis lies in this evolutionary timeline of events that led to sexual reproduction and biological sex. For sperm and eggs to evolve, sexual reproduction must have come first. As a result, the earliest sexual behaviours were likely ‘indiscriminate’, aimed at increasing mating opportunities by attempting to reproduce with all individuals rather than selecting partners based on their biological sex, which was in the early stages of evolving. The result? A natural mix of same-sex and different-sex interactions.
 
For those early species, life was all about maximising reproductive success in challenging environments. Picture a group of primitive animals releasing eggs and sperm into the ocean. The goal was simple: fertilise as many cells as possible. In such scenarios, being overly selective about your mate’s sex could backfire. By directing sexual behaviour indiscriminately, individuals increased their odds of successful reproduction. In this ancestral world, missed opportunities could be far more costly than the occasional same-sex interaction. Evolution, after all, isn’t all about perfection, it’s about what works well enough to pass on genes.
 
The hypothesis therefore suggests that same-sex sexual behaviour isn’t some evolutionary oddity that evolved later, but instead it was simply part of the package. In fact, targeting sexual behaviour exclusively toward the opposite sex may be the derived, more specialised trait that evolved in specific contexts. In other words, same-sex sexual behaviour hasn’t evolved repeatedly in specific animal groups as many scientists have previously argued, but instead persists as a relic of the earliest sexual behaviours.
 
This perspective allows us to recognise some of the biases that have historically stung scientific research. Much of the 19th- and 20th-century work on same-sex sexual behaviour was likely prejudiced by heteronormative assumptions and Euro-American cultural norms, where discrimination against queer individuals may have contributed to framing same-sex behaviour as unnatural or in need of special justification. By shifting our baseline to consider indiscriminate sexual behaviour as the ancestral state, we can move beyond these biases and gain a clearer understanding of the rich diversity in animal behaviour. It reminds us that same-sex sexual behaviour is part of a broader, ancient behavioural repertoire, not some unusual exception.
 
It's important to approach this shift with caution, as science can sometimes be coopted to support subjective and dated beliefs about what is ‘natural’ in humans. It seems in modern times we are frequently seeing science being misused to justify discriminatory positions on gender, sexuality, and behaviour, such as rigid gender ideologies or assumptions about what human identities should or shouldn’t be. This risks oversimplifying complex biological and social phenomena and inappropriately applying conclusions from the animal kingdom to human society.
 
However, the ancestral indiscriminate sexual behaviour hypothesis provides a fresh lens through which to view same-sex sexual behaviour. It suggests that this behaviour isn’t an evolutionary paradox or a costly mistake, it’s a window into the ancient roots of animal behaviour. By recognising same-sex sexual behaviour as a natural and persistent trait, we can better appreciate the diversity of life and evolution’s complex, intricate and messy beauty.

All in all, I ended my trip with 96 bird species seen, including 24 new personal species for Scilly and 4 new species globally (full eBird trip report found here)! I cannot recommend Scilly in the autumn enough for anyone who enjoys birdwatching, and I am already keen to book my trip for next year!

As a post-PhD break, I have just spent a month travelling over land around Canada and the north-east USA. It was an incredible trip, where I got to see a wide-range of cultures in different cities and towns, as well as some top quality birds. Due to the nature of the trip, I was unable to take my camera for wildlife photography, but it was still great to get out into natural spaces and explore the local wildlife!

The real highlight for me was my final week at Cape May, in the southern tip of New Jersey. Cape May is famed for its birding, particularly during the spring and autumn when huge numbers of migratory species are seen. The narrow peninsula acts a bit like a funnel to the migrating songbirds, hawks and waders, channeling them towards the very tip of the peninsula where they briefly rest before making long journeys over sea or land. This effect is very noticeable when birding at specific spots, such as the Cape May Bird Observatory's Hawkwatch platform, where one morning we had 8 bird of prey species including 35 ospreys and approximately 50 turkey vultures. Having never birded this side of the Atlantic before, I decided to book onto a tour group so that I could have a little help with identifying unfamiliar species. This was much needed as I ended my time in North America with 125 species I had never seen before! My entire eBird trip report can be found here.

I'm really pleased to say that I passed my PhD Viva today without corrections, which means I am now officially a Doctor of Biology! The viva involved an interview process with two professors in similar fields of biology asking lots of questions as to the reasoning behind my research as well as my key findings. Despite being a nerve-wracking process, it was also a great opportunity to talk to experts in the field as to how my research fits into the wider context of evolutionary and ecological research. It goes without saying that I couldn't have achieved this without the professional and personal support of my supervisors (Ben, Josh and Ella) and the rest of the research group at Oxford - thank you everyone and on to the next chapter!

Spotted flycatchers are very much a 'Brill bird' to me. Brill, a small village on the Buckinghamshire side of the Bucks/Oxon border, is where my parents live and where I grew up. The unusual thing about the village is that it is on top of a hill at roughly 120m altitude in an area of generally very flat land. To me, this seems a likely reason as to why it draws in a few migrating species during the autumn that hit higher land on their long flights. Spotted flycatchers are a migratory species which breed across the UK and overwinter in tropical Africa. The UK breeding population has taken a real hit over the last few years, dropping by 92% between 1967–2020, making them a red list species that aren't particularly easy to find. The reason for this severe decline is somewhat unclear, but is likely linked to climate change at their wintering sites as well as a loss of insects and suitable habitat in the UK. Despite this serious decline, I came across no less than four on a walk through the village common today, which was a real treat!

I had another great trip to Scilly with my family, with plenty of time to get around the islands and take photos of nature. The birdlife is very different at this time of year compared to when I visited in April, with many fewer species that are passing through on their migrations. However, this time of year is great to see the (mostly) resident shorebird species as their feeding behaviour works like clockwork with the rising and falling of the tides.

This year I was lucky enough to take part in the centuries-old tradition of the Swan Upping. This is a five-day journey up the Thames where a flotilla of traditional skiffs manned by Swan Uppers row 79 miles from Sunbury-on-Thames to Abingdon.

As a child, I remember hearing that widely-told fact "Did you know the Queen owns all the swans in the country". But this is not quite the case! In fact, the Crown holds the right to claim ownership of all 'unmarked' mute swans swimming in open waters across the UK. Historically, rights of ownership were granted by the monarchy to various individuals and organisations, as swans provided a valuable food for banquets. Today, only three organisations have retained their ownership rights. Abbotsbury Swannery own the swans that they mark at their site in Dorset (where I have used data for some of my research), and two London livery companies (the Vintners and the Dyers) own those which they mark on the Thames - which is where the Swan Upping comes in!

Previously, swans would have been claimed by physically marking the top of their beaks, but these days they are marked with metal leg rings that are widely-used in avian research. During the Swan Upping, every third swan found along the route is ringed and claimed by either the Crown, the Vintners, or the Dyers. However, the method of marking birds is not the only thing that has changed. While swans used to be claimed for food, they are now a protected species and are no longer eaten. The primary aim of the modern day Swan Upping is that of conservation and education. 

Conservation is essential for the swan population on the River Thames, as boat activity, fishing, and riverbank construction has disrupted their natural habitat. Additionally, predation by non-native species such as mink, and injuries from discarded fishing tackle, pose significant threats to swans. The King’s Swan Marker works closely with swan rescue groups to protect swans on the river, helping to ensure the population's survival. The annual Swan Upping also provides a valuable opportunity to collect data on how the population is fluctuating over time with changes in land-use, while also tracking how other bird populations (such as geese, ducks and grebes) are changing.

Education also plays a large role in the Swan Upping. Children from local schools visit the Swan Uppers along the banks of the River Thames, gaining the opportunity to learn about swan biology and the habitats they need. These children also get the opportunity to see cygnets up close, which is always inspiring!

Finally, I recently helped at a ringing demonstration for a local environmental group. Here, we got to show those who attended the wonderful diversity of species across the site, which made me realise how sharing these types of data collection with local communities can encourage people's appreciation of the natural world, promoting conservation of key habitats even in urban settings.

I​ have just returned from an incredible trip to The Isles of Scilly, where I had some really amazing wildlife encounters. I have been visiting Scilly every year all my life, and as mentioned many times on this blog, it is a very special place for wildlife. However, given the geography of the islands, it is a particularly special place for birdwatching during spring and autumn when it hosts a wealth of migratory species that drop down during their journeys to-and-from breeding grounds. I have only once visited the islands outside of mid-summer, and I am too young to remember much of what we saw!

I started the trip with a calm crossing on the Scillonian III ferry, where the holiday began with sightings of many manx shearwaters, guillemots and razorbills in rafts between Land's End and Scilly. It's extraordinary to think of the journey these birds have made, with many of our Manxies migrating across the Atlantic from South America to breed in Scilly (and other areas along the western coast of the UK). When I arrived on St Marys, I had a few hours before my mum would join me on the islands. I walked to some of the nature reserves on the island, managing to see the stunning purple heron which had been on the islands for a few days, in addition to a soaring hen harrier - both Scilly firsts for me!

In total, I saw 85 bird species over the course of the week (eBird trip report found here) - it certainly isn't a trip I'll forget any time soon!

This year I was really pleased to be shortlisted for the British Ecological Society's Elton Prize, awarded for the best research paper in Journal of Animal Ecology written by an early career researcher. As part of this shortlisting, I wrote a blog post for Animal Ecology in Focus outlining the background to our research on age-assortative mating in bird populations - read it here!