A Chinese mitten crab has been recorded in Scotland for the first time, posing a potential threat to local biodiversity and habitats.

The invasive crab species is already known to have populated rivers in the UK as far north as the Tyne, but this sighting in Glasgow's River Clyde confirms its migration over the Scottish border.

The Chinese mitten crab, named for the furry mats covering its claws, is one of the top 100 worst alien species in the world, according to the International Union for Conservation of Nature. It threatens biodiversity by competing for food, preying on native species and causing severe structural damage to riverbanks through burrowing.

Crabs on tour

The specimen found in the River Clyde, the remains of a female mitten crab, is the first recorded sighting north of the border.

The Chinese mitten crab (Eriocheir sinensis), is native to East Asia but is now found across NE Europe and the USA. It was first recorded in the River Thames in 1935, probably introduced by shipping. In the late 1980s the mitten crab began to disperse westwards along the Thames, and there are now well-established populations of E. sinensis in a number of Welsh and English rivers, as well as a single sighting in Ireland in 2006.

The left claw of a male mitten crab (Eriocheir sinensis).

The International Maritime Organisation (IMO) has set out standards for the control and management of ships’ ballast water and sediments, in an effort to control the transport of species to non-native waters.

Potential threat to biodiversity

Mitten crabs may target the eggs of salmon and trout, according to recent research by Royal Holloway University of London (RHUL) student Jessica Webster and supervisors Dr Paul Clark (the Museum) and Dr David Morritt (RHUL).

Dr Clark sees the recent discovery as a major threat:

"An established River Clyde Chinese mitten crab population could pose an enormous environmental risk to the salmon and trout in this catchment (…) if this reported Clyde specimen came from a deliberate human release, the environmental authorities need to urgently consider what appropriate actions are required to prevent such introductions happening again in the future."

Dr Clark is studying the biology and behaviour of mitten crabs to better understand how we might control their migration and ultimately eradicate alien populations outside East Asia.

See live mitten crabs at Science Uncovered

As part of the Museum's annual festival of science on 26 September 2014, Dr Paul Clark and Dr David Morritt will be showcasing some live Chinese mitten crabs and talking about their work on the biology and behaviour of this problem species.

Come along to Science Uncovered to see these and a whole host of other specimens, take part in activities and meet Museum scientists.

The spotted green pigeon, a mysterious species collected in the 1700s, turns out to have been a flying relative of the dodo that likely lived in the trees of the South Pacific.

Only two specimens of the pigeon were ever described, in 1783, and since then one has gone missing. The location they were collected from was not recorded, but they are associated with South Pacific voyages. The only remaining specimen is held at the World Museum (formerly Liverpool Museum), National Museums Liverpool.

Quest for identity

In its original description, the spotted green pigeon was said to closely resemble the Nicobar pigeon, a bird native to Indonesia that prefers to live on small remote islands. This, and it's obscurity, led some to speculate that the spotted green pigeon was just an unusual variety of the Nicobar pigeon.

Determined to find out once and for all, the World Museum asked our bird expert Hein van Grouw and colleagues in Australia to investigate their specimen. Using detailed morphological analysis and genetic testing, the team identified the spotted green pigeon as a distinctive species in its own right.

The only remaining specimen of the spotted green pigeon.

Photo by Hein van Grouw.

Dodo connections

Preliminary results from the genetic testing reveal the pigeon is in the same family as the dodo and its extinct flightless relative the Rodrigues Solitaire. It's somewhat of a mystery how the specialised flightless dodo got to its isolated island habitat, but finding more relatives can help clarify the picture. The addition of the spotted green pigeon to the lineage may add some evidence to the 'stepping stone hypothesis', which suggests ancestors of the family island-hopped from India or Southeast Asia.

van Grouw is completing his morphological analysis that will help determine what kind of lifestyle the spotted green pigeon had. It was originally described as having short wings, suggesting a ground-dwelling lifestyle like the dodo, but this turns out not to be the case, and it is more likely that it lived in the trees eating fruit and berries.

Gone already

Determining the spotted green pigeon as a separate species has another consequence. Since no others have ever been seen, it can confidently be added to the extinct species list.

• Find out more about our Bird Group and our stunning collections

Birds targeted by cuckoos develop sophisticated egg patterns to help them recognise the fakes.

Cuckoos infamously lay their eggs in the nests of other birds, forcing them to care for their young. But species that are repeatedly targeted by cuckoos have developed a range of complex egg patterns to help distinguish the invader's eggs and kick them out of the nest.

Cuckoos will hatch before their nest-mates and throw them out, so that the parent birds will only raise the cuckoo. When a host bird recognises a cuckoo egg, they may puncture it or throw it out the nest before it hatches.

Signature patterns

Scientists from Harvard and Cambridge Universities developed a pattern-recognition software called NaturePatternMatch that mimics the way birds see the world. Using the extensive egg collections of the Natural History Museum at Tring, they then analysed the eggs of eight bird species commonly targeted by cuckoos.

They found that where cuckoos had developed accurate copies of host-bird eggs, the host birds had in turn developed more complex egg patterns. 'The egg patterns on cuckoo and host eggs reveal an evolutionary arms race,' said lead author Dr Mary Caswell Stoddard from Harvard University.

Samples of cuckoo's eggs in host bird clutches from the Museum's collections. Cuckoo's eggs are often bigger than their host's.

'In many cases, cuckoos have evolved excellent egg mimicry in order to trick host birds into accepting foreign eggs. In these instances, host birds have evolved excellent egg pattern signatures on their own eggs as a defence.'

The host birds studied used different techniques to set their eggs apart. Some females of the same species, such as the great reed warbler, laid very different eggs to each other, but very similar eggs within their own nest. Others, such as the brambling, lay eggs with unevenly spaced, sparse markings, making a good signature.

Collections and tools

Museum egg and nest curator Douglas Russell said he was 'fascinated by the insights [this paper] provides into the particular mechanisms that appear to be involved.' The extensive bird collections, which cover 95% of all bird species alive today, are involved in numerous studies.

'They can contribute to research as diverse as understanding migratory routes and investigating chemical contamination of the environment over time.'

The NaturePatternMatch software may also be used in a range of projects. 'How do animals recognize their neighbours, enemies and kin? How have visual signals evolved to maximize distinctiveness? Computer vision tools like NaturePatternMatch will help us answer these important evolutionary questions,' said Dr Stoddard.

• Read the full paper online
• Find out more about our bird collections