New Species Of Bird Identified In India And China

Scientists discover a new bird species many years after they first noticed it sang a different song

A new species of songbird has been discovered in northeastern India and in neighbouring parts of China after it was found to be distinct from a close relative, which it strongly resembles. This discovery, which resulted from detailed analyses of the birds' songs, DNA, physical appearances, life histories, and geographical and altitudinal distributions, was reported this week in the peer-reviewed journal, Avian Research. The new species, named the Himalayan forest thrush for its habitat preferences, was given the scientific name, Zoothera salimalii, in honour of Sálim Ali (1896–1987), India's most famous ornithologist and wildlife conservationist. The Himalayan forest thrush is only the fourth new bird species identified in India since its Independence in 1947.

"This latest finding of a whole new species of thrush from India, which has a 300-years long and rich history of ornithological explorations, reminds us that documentation of Indian avifauna is far from complete", said ornithologist Rajah Jayapal, Principal Scientist at the Sálim Ali Centre for Ornithology and Natural History, who was not part of the study.

The newly-identified songbird was hiding in plain sight

Historically, avian taxonomy was based upon similarities in physical appearances: birds that look alike were classified either as the same species or as subspecies of the same species. But with the advent of intensive and increasingly comprehensive DNA analyses, researchers were initially surprised to learn that some populations, or taxa, that share strong physical similarities have highly divergent DNA and may not even be each other’s closest relatives.

But short of dragging a PCR and DNA sequencer into the field, how can an interested observer distinguish these species? The birds themselves conveniently provide important auditory clues to those who take the time to listen to them: research on birdsongs and avian vocalisations has found that many look-alike species do not sound at all alike. Further, these physically similar taxa do not respond to each other's distinct songs, indicating that they know who they are even when people do not. Such look-alike taxa that can be mistaken for each other are known as "cryptic species".

Although many cryptic species are not close relatives, other cryptic species may form a species complex.

"A 'species complex' is simply a group of closely related species", said lead author, Per Alström, based at Uppsala University and the Swedish University of Agricultural Sciences. Professor Alström headed an international team of scientists based in China, the United States, India and Russia.

Professor Alström is an expert on Asian songbirds, such as the Asian thrushes, Zoothera species. These medium-sized songbirds are close relatives that can be so confusingly similar in appearance that some are indistinguishable in the field. A particularly baffling group form the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex, most of which were thought to be the same species.

Except they aren't.

"[I]n this case ... the distinctness of the different species has been overlooked due to their great similarity in appearance", said Professor Alström in email.

Two songs, two habitats ... and two bird species?

For this reason, Zoothera thrushes may not be what they appear to be. Back in 2009, before cryptic species were widely appreciated by ornithologists and other experts, Professor Alström and Shashank Dalvi, from the Centre for Wildlife Studies in Bangalore India, were conducting field work at high elevations in Arunachal Pradesh, northeast India, when they noticed a "plain-backed thrush" in a coniferous and mixed forest singing a song that was unusually rich and melodic.

Not only was this bird's song "all wrong", but its habitat was, too. Professor Alström and Mr Dalvi became intrigued after comparing this song to the "scratchier" and faster song of the more familiar "plain-backed thrush", Zoothera mollissima, which lives on rocky slopes above the tree line (higher than 4200 metres/13,800 feet above sea level) in the same area.

"Per is the genius behind this discovery, because he has an incredible ear and memory for fine details of bird song (perhaps unparalleled for Asia)", said team member and co-author, Pamela Rasmussen, an integrative biologist at Michigan State University, and coordinator of MSU’s crowd-sourced global bird sounds website, AVoCet.

"Basically, he heard one song type coming from the barren alpine zone, and a very different song type coming from the forest below", explained Professor Rasmussen in email.

Although it had been noticed before, this song difference had been explained away as an "alternate song" of the "plain-backed thrush". But Professor Alström and Mr Dalvi were not convinced that these distinct songs were produced by the same species, especially when they noticed the habitat and behavioural differences of each bird.

"We could not detect any differences in appearance between them, although we never saw them next to each other, and the ones in the forest were exceptionally shy and hard to get good views of", said Professor Alström in email.

“It was hidden in plain sight. It was so similar to the Plain-backed Thrush that unless you hear the song, it is hard to make out the difference”, agreed Mr Dalvi.

"We were nevertheless convinced that these two forms were different species -- which nobody had ever suggested before", said Professor Alström.

The team decided the best way to investigate and test their idea was to collect and analyse a variety of data, including song, morphology, ecology and molecular data, for all members of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex.

And so the team went to work, collecting audio recordings from throughout the geographic range of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex. They recorded songs from 45 wild "plain-backed thrushes" and from 10 wild long-tailed thrushes. When the team listened to those recordings, not only could they hear differences in the songs, but they could identify those differences just by looking at the different audio patterns represented by the sonograms:

Analyses of the sonograms revealed that four song variables (song duration, top frequency, bottom frequency, frequency bandwidth and peak frequency of strophes) of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex formed distinct clusters, indicating these auditory variables were reliably maintained by different individuals within each population (Figure 13):

Because songbirds primarily rely upon song and other auditory signals to identify and attract potential mates, and to defend territories against rivals, this is an important mechanism for maintaining species boundaries and for avoiding hybridisation, particularly when look-alike species occur near each other. But knowing this, listening carefully is also an important way for people to identify bird species without actually seeing them, and to distinguish between species that look similar.

These species are not identical although they look very similar

Since it is easy to overlook or to explain away small visual differences, it was Professor Rasmussen's task to precisely document the physical features of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex, particularly for the two taxa -- by now dubbed the "Himalayan forest thrush" and the "alpine thrush" -- that were found singing near each other on that misty mountainside so many years earlier. But it was important to determine whether these populations were different enough to warrant further investigations.

"This is important not only in demonstrating that the groups differ in structure, but also in determining which groups are already named", said Professor Rasmussen. A "named" species is one that has already been discovered and formally described by someone else.

To do this, Professor Rasmussen measured the shape of the beak, wings, tail and tarsus (leg bone) and the plumage colours from holotype specimens held by 15 museums in seven countries. A holotype is the actual specimen described in the formal scientific literature, and as such, each one is special.

The structural measurements revealed consistent differences in plumage and morphology (physical structure) between birds from each of these populations (Figure 2):

As you can see from the overlapping clusters of measurements in the above figure, these groups do look quite similar -- but as you also can see, they are not identical.

Interestingly, the holotypes' plumage colours were more distinct, providing better information to aid identification (figure 3):

Taken together, structural and plumage colour measurements revealed consistent differences between populations of these birds so they could be assigned to a particular species in the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex. Further, it was confirmed that the bird singing that melodic song in the forest of the eastern Himalayas was distinct but had not been formally named.

These birds occupy different habitats and have different personalities

Field investigations revealed that each member of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex occupy distinct habitats, too.

The alpine thrush breeds above the tree line on stony boulder-strewn ground covered with mosses, lichens, short grasses and a few small scattered bushes.

In India, the Himalayan forest thrush occupies coniferous and mixed forests with lush undergrowth that lie below the tree line. In China, the Himalayan forest thrush occupies very different habitat, described as "steep slopes with bamboo and rhododendron scrub and rocky outcrops and a few scattered conifers, at or just above the upper tree limit" (3350–3500 metres/11,000+ feet above sea level). The Himalayan forest thrush is an altitudinal migrant that moves down the mountainsides after breeding season.

A third member of the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex, which had previously been described as a subspecies, is the Sichuan forest thrush. This species lives in a variety of forest types located even lower down the mountainsides, between 2500 metres (8200 feet) and 3300 metres (11,000 feet) above sea level. These taxa may also be altitudinal migrants since several individuals were reported from 1067 metres (3500 feet) and 1370 metres (4500 feet) above sea level in November (after breeding season).

These birds also have different personalities. The alpine thrush is very easy to observe, and often sings from an exposed perch, as you might expect since it lives in open habitat and there are few predators above the tree line. In contrast, both the Himalayan forest thrush and the Sichuan forest thrush are secretive, and even when singing, they remain hidden within the tree foliage.

DNA reveals that one species is now three -- or maybe more?

The idea that the different populations of birds in the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex are not simply regional variants was further bolstered by the genetic data. DNA analysis indicated that the three "plain-backed thrushes" have been genetically separated for almost as long as humans and chimpanzees have been genetically separate -- indicating these birds are all distinct species (Figure 14):

This genetic family tree estimated that the Himalayan forest thrush and Sichuan forest thrush diverged at least 3.4 mya (and probably 4.5 mya) and further, indicated that they are sister species (each other's closest relatives). The other taxa in the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex are more distant relatives.

Based upon song, morphology, ecology, and phylogenetic data, the authors propose these name changes to the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex:

1. the high-elevation "plain-backed thrush" should be renamed the 'alpine thrush', whilst retaining its original scientific name, Zoothera mollissima, in accordance with international nomenclatural rules (pale blue box; Figure 14)
2. the "plain-backed thrush" present in central China, which was previously treated as a subspecies in the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex, should be elevated to full species status and renamed the Sichuan forest thrush, Zoothera griseiceps (yellow box; Figure 14)
3. and of course, the star of this story, the newly-identified unnamed "plain-backed thrush" that sings a lovely song and dwells in lower elevation coniferous and mixed forests, should be named the Himalayan forest thrush, Zoothera salimalii sp. nov. (orange box; Figure 14)

But by this time, if you've been looking carefully at that phylogeny (Figure 14), you may be wondering what that purple box is all about: indeed, this may be a fourth species within the “plain-backed thrush” (Z. mollissima)-long-tailed thrush (Z. dixoni) complex. This species, also unnamed, resides in China. It currently is referred to as the "Yunnan thrush" by the authors, who are already working to confirm this preliminary finding.

More cryptic bird species await identification in India

Identifying new species of birds is uncommon these days, and most of those discoveries are made in South America. In fact, the Himalayan forest thrush is just the fourth new species identified in India since it became an independent country in 1947. But ornithologists think more such discoveries are waiting in the misty montane forests of India and China because these challenging landscapes are so poorly known.

"[T]his study, led by Dr Per Alström describing a hitherto-unknown thrush species from the eastern Himalayas in India and China, is truly a milestone in the history of Indian ornithology", said ornithologist Rajah Jayapal, Principal Scientist at the Sálim Ali Centre for Ornithology and Natural History in India, who was not part of the study.

"This is, in fact, the latest in his series of investigations in the Subcontinent to study species limits in birds and to discover cryptic taxa", explained Dr Jayapal in email.

"Mountains in Himalayas and adjacent southwestern China encompass one of the world['s] hotspots of avian diversity, probably due to its complex evolutionary histories and heterogeneous environments", said evolutionary ecologist and ornithologist Yang Liu, Associate Professor at Sun Yat-sen University in China, who was not part of this study. "However the description of neglected and cryptic diversity in species level is still on-going."

In addition to the phylogenetic data, this elegant study integrates multiple independent sources of evidence -- birdsong, morphology, behaviour, ecology, and geographic and altitudinal distributions -- to support the identification and description of a bird species that is new to science.

"One of the most interesting pattern[s] here is that closest relative species diverged in morphology, acoustics, ecological niche and genetics along altitudinal and environmental gradients", explained Professor Liu in email.

This rigorous approach is particularly powerful when identifying cryptic species.

"The most challenging task in Indian ornithology today is to unravel the cryptic species and we strongly suspect there are many more among Indian avifauna", explained Dr Jayapal.

"But the stringent federal laws in India and its neighbours to protect their biodiversity, though well-meaning and purposeful, do not have exclusive provisions to facilitate taxonomic research, thus seriously hampering our efforts to systematically document the region’s rich biodiversity", explained Dr Jayapal, who went on to say that "research permits involving collection of biological samples like tissues or blood from wild animals for further genetic analyses take unduly longer time and often persistent efforts on one’s part."

The difficulty in obtaining collecting permits is likely the reason why nearly all the molecular studies from India are dependent upon old museum specimens -- the majority of which were collected during the British colonial regime and are currently housed in major museums around the world.

"But these old specimens are poor substitutes for fresh biological samples and require more expensive and superior techniques to extract high-quality DNAs", explained Dr Jayapal. He pointed out that some species that are found only within India's borders are not represented by any museum specimens, so they remain poorly known or completely unknown.

New Species Of Bird Identified In India & China | @GrrlScientist

Sources:

Per Alström, Pamela C. Rasmussen, Chao Zhao, Jingzi Xu, Shashank Dalvi, Tianlong Cai, Yuyan Guan, Ruying Zhang, Mikhail Kalyakin, Fumin Lei and Urban Olsson (2016). Integrative taxonomy of the Plain-backed Thrush (Zoothera mollissima) complex (Aves, Turdidae) reveals cryptic species, including a new species, Avian Research 7:1-38 doi:10.1186/s40657-016-0037-2