There are roughly 10,000 species of birds on the planet. They are a hugely diverse group which exhibit a vast range of shapes and sizes, life choices and behaviours. As such they are a joy to study! Researching birds has an intrinsic value for anyone who enjoys them but its benefits extend far beyond the interests of the ornithologically obsessed. Understanding birds can help shed light on more cryptic groups for example understanding how other lineages speciate and diversify. More importantly birds have much wider impacts via the roles they play in ecosystems. Hummingbirds and sunbirds pollinate flowers whilst toucans and hornbills disperse seeds. From eagles to robins, predatory birds control the numbers of invertebrate and vertebrate prey alike and scavengers take care of all the dead bodies. These ecosystem functions provide important and valuable services to humans, some of which can be quite surprising! For example, vultures do not rank highly amongst many people’s favourite birds however they play a crucial role in removing carrion and this prevents the spread of disease. We need to know how important birds are because, in a world fraught with anthropogenic issues, we need to know what will happen if we lose any of them.
The Job
My colleague Nico and I have joined The Biodiversity Group, part of the Edward Grey Institute of Field Ornithology within the Zoology Department of Oxford University. Our job is to measure functional traits in all of the world’s non-passerine birds. We will be spending the majority of our time in the Natural History Museum in Tring, Herts. This off-branch of the main museum in South Kensington houses their bird collection, one of the largest and most complete collections in the world with roughly 95% of bird species. This will add to a global bird dataset allowing the analysis of a huge amount of information to better understand the diversity of birds.
The Measurements
Functional traits are physical characteristics of an organism which are indicative of its ecology:
- Beak dimensions (length, width and depth) are related to the feeding ecology of a bird. At one end of the spectrum, wading birds such as curlews have long, slender bills for probing sediment whilst, at the other end, finches have short thick bills for crushing seeds.
- The relationship between the length and width of the wing tells us about the mobility of a species. Birds which spend much of their time in the air such as migratory swallows have long tapering wings which allow them to travel great distances. Other species such as wrens have short, fat wings which are sufficient for flitting from bush to bush but do not take them far from the ground. The mobility of species is important for their ecology and evolution as more mobile species are able to disperse more easily (more vagile) and overcome geographic barriers such as mountains or rivers whilst the less mobile species tend to be geographically limited.
- The leg length is similarly indicative of mobility as adept fliers such as swifts and shearwaters tend to have stunted legs whilst largely terrestrial birds have large supportive legs.
- Finally tail length is important for flight (allowing stability and steering) but it is also a trait which often varies between the sexes so can be used to measure sexual dimorphism. These are the traits we will measure in four specimens of each species: two male, two female.
The Birds
The birds (Aves) are a class of vertebrate animals which evolved from small therapod (predatory) dinosaurs in the late Jurassic (c. 160 Ma). Like other organisms, this class is split into orders. The number of orders depends on the classification system used and ranges from 27 to 40 orders. Some groups such as the fowl are unambiguously listed as orders whilst the variation in the list tends to come from a few small groups which may or may not be sufficiently different from their closest relatives to be raised to order status. For example, the large, flightless ostriches, rheas and cassowaries could be classified one order or multiple orders depending on how fundamentally different they are believed to be but also depending on their relationship with other groups. I tend to prefer elevation of unusual groups to order level in agreement with more modern taxonomy and from here I will be using the classification system of the International Ornithologists' Union. As implied, there is not necessarily a correct way to classify birds. All animal species are derived from a bifurcating tree of continuous evolution and we can try to ascertain true evolutionary relationships. However labelling orders, families, genera and species can be more arbitrary and different taxonomists have different criteria.
The order that stands out the most among the birds are the Passeriformes (‘sparrow-shape’), an order of over 5,000 species comprising over half of the world’s species. These are the highly diverse perching birds including larks, wagtails and swallows, warblers, tits and thrushes, crows, sparrows and finches. Their apparent diversity placed them higher on the list of species to measure and so they have already been done (almost). That leaves Nico and I with the rest: less than half of all bird species but still over 3,000 species within 39 orders of dazzling variety. We are both excited about the shear variety of lifeforms we are going to handle!
