Mega-evolutionary dynamics of the adaptive radiation of birds


Nature bills

The idea to 3D scan the bills of the world’s 10,000 bird species from museum collections has always seemed like an ambitious undertaking. However, after two years of data collection, months of analysis and the input of hundreds of citizen scientists, the first study resulting from our work was published in Nature last month.

This initial, wide-ranging exploration of bill diversity, compared over 2000 species from across all genera, considering the full range of present-day bill shapes.

The diversity we see in bill shape today is extraordinary and studying this characteristic can tell us a lot about species and how they interact with their environment- from foraging, hunting and eating food, to preening and nest building. Traditional methods of gathering information relating to bill form have often relied on length, depth and width measurements alone, missing many key elements of shape, such as curvature. By 3D scanning bills, we have been able to capture far more detailed information, providing a true reflection of bill diversity.

It would have been impossible to collect this information from birds in the wild so our study has been reliant on the incredible ornithology collections at Manchester Museum and the Natural History Museum in Tring. These archives of biodiversity have allowed us to create fantastically detailed models through access to such a broad variety of species, alongside curatorial expertise and work space.

One of the most novel aspects of our study was the way in which much of our initial data- the 3D scans- was processed through the input of citizen scientists from around the world. With each scan requiring landmarking by at least 3 different people, this in itself was a huge task and one that would not have been possible without such a collaborative effort. By helping us place key points and trace edges on every scanned bill, online volunteers assisted in turning these hugely complex 3D models into data that could then be analysed.

From this we have been able to highlight that the majority of bill diversification evolved quickly and, once extremes of shape were reached, the amount of change slowed down significantly as birds began to fill increasingly narrow ecological niches. As a result of this initial fast change and huge variety of form, birds have been able to exploit the equally wide range of habitats and sources of food.

The full paper can be read here and, excitingly, has also received some fantastic press attention, including a discussion of our findings with project PI Dr Gavin Thomas on both the Nature podcast and BBC Inside Science (interview starts at 20:00 minutes) – if you prefer a good listen, rather than a good read. A selection of our online coverage is listed here:

Audubon – Post-docs Dr Chris Cooney and Dr Jen Bright spoke to Audubon magazine about our findings and how they build upon our previous understanding of bill diversity.
BBC Science & Environment – ‘How birds of a feather evolved together’
New York Times – ‘Finding the Speed of Evolution in a Study of Bird Beaks’
Natural History Museum – Our study wouldn’t have been possible without the incredible ornithology collections at the Natural History Museum. This statement highlights our reliance on this resource as well as how our data can be used in the future.
University of Sheffield – A summary of our project and findings as part of the Department of Animal & Plant Sciences at the University of Sheffield.

If reading about our work has caught your interest, it’s not too late to contribute. Our crowdsourcing site is still very much up-and-running as we continue to increase our data relating to all extant species. Whether you want to browse our scan gallery or have a go at landmarking, everyone is welcome.

A tale of two bills: the reedhaunters

facebooktwitterReedhaunters 2Our research is reliant upon the Natural History Museum’s ornithological collections- comprising thousands of specimens, amassed over centuries from across the globe, preserved, recorded and studied. The scale and scope of our project means we come into contact with a huge array of this material every day, working across taxa to select individual specimens that act as representatives of a species for our dataset. We handle them, assess their condition, transcribe and photograph their label data, create 3D images of their bills and return them to their place amongst the taxonomically arranged cabinets. This is typical of the way wide-ranging scientific research utilises natural history collections- as ordered snapshots of biological data- but this is only one way of viewing and using them.

Having previously worked on the collections from a historical perspective, where focus more often lies on the individual artefact, studied and prized for its own story, it has been an interesting shift to consider these alternative approaches to collections. There are still occasions, however, when the habit of checking specimen labels, not just for sex and locality data, but also for handwriting, collector’s names and annotations can highlight the biography of a specimen and the species it represents. The reedhaunters, comprising only two species, are a prime example of this.

The specimen of straight-billed reedhaunter (Limnoctites rectirostris) we selected for scanning and landmarking is identified as a type- the specimen from which a species was formally described. The Natural History Museum is keeper of the largest number of ornithological types in the world, stored securely from the main series, and often harbouring their own intriguing stories alongside their immense scientific value.

The labels on this particular specimen revealed that the bird had been collected by none other than Charles Darwin  (1809-1882) during the second voyage of HMS Beagle before being sent to London via the great ornithologist and scientific artist John Gould (1804-1881). It remained one of the only such specimens known to science for a further century. Furthermore, Gould used this specimen in his illustrations for the Zoology of the voyage, a publication that immortalised the collecting activity on the infamous expedition:

John Gould's original illustrations of the Reedhaunters, with Limnoctites rectirostris thought to have been painted directly from the type specimen

John Gould’s original illustrations of the Reedhaunters, with Limnoctites rectirostris thought to have been painted directly from the type specimen

The reedhaunters are marsh-dwelling ovenbirds that were first collected by Darwin whilst in Uruguay in the 1830s. As with many of his ornithological specimens, Darwin sent the prepared skins back to London where John Gould set about studying and identifying them. In so doing, Gould created the new genus Limnornis for the two species, and (particularly interesting for our study) named them individually according to their bill differences, the straight-billed reedhaunter (Limnornis rectirostris) and the curve-billed reedhaunter (Limnornis curvirostris).

Our scans of the curve- and straight- billed reedhaunters, with the former taken from Darwin's actual 19th century specimen

Our scans of the curve-billed and straight- billed reedhaunters, with the latter generated from Darwin’s actual 19th century specimen

Since Gould’s original identification of these species and despite Darwin himself saying he was unable to notice any behavioural differences between the species, they have undergone a number of taxonomic revisions. Increased understanding of differences between the two has seen them widely placed in separate monotypic genera (Limnornis and Limnoctites) but they have still widely been regarded as each other’s closest relative.

Building on this, contemporary research has highlighted that beyond broadly similar plumage, there are more significant differences between these species than their historical treatment would have us believe. With significantly different tail structure, nest building behaviour and egg colouration (L. curvirostris lays greenish-blue eggs, unusual within Furnariidae), additional studies considering distribution and molecular systematics have built a case for their long-held taxonomic relationship to be reconsidered. You can read one such paper in full here.

The whole process of working with historical specimens requires learning from the physical artefact, building on our existing knowledge by combining new methods and insights with this long-ago collected material. So when you log on to MarkMyBird and begin landmarking a bill, spare a thought for where the original specimen came from, at what time, whose hands it has passed through or, indeed, what new light may be shed on its relationships with other species as a result of modern scientific studies.