With soft steps, careful not to rustle any leaves or crack the twigs strewn about before her, Xing Xiaoying pursues the Light-vented Bulbul songbird and takes aim with her long, camouflaged microphone. This ornithologist is on the hunt for music.
Over the last couple of years, Xing has recorded more than 4,000 songs from the southern songbirds that have migrated north in China, likely because of climate change. But her research has shown that the birds' migration seems to have come at the cost of complexity and variance in their songs.
The PhD student of ornithology with the Chinese Academy of Sciences talks about her discovery, which was published last month in the British-based Journal of Evolutionary Biology.
Why are the southern songbirds heading north? And how long have they been doing this?
The Light-vented Bulbul is typically a southerner [in China]. Its body and wings are structurally unsuitable for long flights. They like to use thick bushes and heavy foliage to find food, nest, play and rest. They don't have much of a spirit for adventure, either - they rarely visit hilltops more than a couple of hundred metres high. They had long lived closely to human settlements to the south of the Yangtze River and built up large colonies in almost every southern province. They're so chatty and sing so loudly that the bird [also known as the Chinese bulbul] can hardly escape the ear of a birdwatcher.
The first sightings of the bulbuls in northern China were reported in the 1930s, but they remained rare until the 1990s. Now sightings are reported all over the place, stretching [nearly 2,000 kilometres] from Xian [in Shaanxi province) to Dalian (in Shandong province). Their songs can even be heard now throughout the year in Shenyang [in Liaoning province].
The warming climate must be a key reason. In many parts of the world, climate change has enabled some birds to move farther north. We are deeply intrigued by this phenomenon. We desperately want to know how they adapt to the new environment.
What kind of singers are they?
Their songs are loud, tireless, sophisticated. In the south, an individual could sing many different types of songs, each containing useful messages. Our team recorded more than 100 song types in several southern provinces. In contrast, magpies have only a few songs in their entire repertoire. If a male bulbul cannot master the 'pop songs' of its community, it will probably never find a mate.
What happened to that singing tradition among bulbuls in the north?
We recorded about 2,900 songs in the south and found more than 100 types. In the north, we recorded about 4,400 songs, but they were so boring! With our best efforts, we were able to identify just seven song types. We scratched our heads for a bit to find an explanation for this.
One possibility is the 'founder effect' - where birds [that founded new colonies in the north] came from a few small southern families that could sing only a small subset of … song types and syllables, thus decreasing the total variation. Just as most southerners living and working in Beijing speak Putonghua instead of their native dialect, these northern bulbul colonies use a more or less unified type of language to communicate.
Your earlier research also showed that there was greater genetic variety among northern bulbuls compared to the south. Why are the northern birds' songs not as diverse?
Genetic information can be passed down only from one generation to the next. Songs, however, may be passed from one bird to another. Bulbuls learn songs from others. Those on the move have a greater chance of meeting new birds than those that stay home. The absence of geographic barriers such as big mountains in northern plains also encourages exchanges among different communities of the birds. It is common for a genetically sophisticated society to share a common culture.
How do you feel about the research process?
When I started, I thought it would be boring. What can you expect from a bird? How can you tell the difference between one song and another when they all sound similar to the untrained ear? But the more I followed the birds in the wild, and the more I analysed the patterns of their songs in the lab, the more I loved the job, because I was able to decode more messages from their sophisticated singing patterns. Now I am totally absorbed by it.
It is certainly not the most enjoyable and easiest work all of the time. The bulbuls are early risers - sometimes they start singing at 4am, and we had to get up for that. While it was nice to take a field trip into the woods to sample the songs, frustration sometimes kicked in when I did the work in a park or a residential compound, where people would shout and yell and run after the birds. The laughter and noise made our recordings unusable.
Analysing the songs with a computer was also a time-consuming and boring process. How many hours did it cost me? I am too tired to calculate. The job not only requires patience but lots of knowledge about the bird you are listening to.
Does the migration of these birds come as a relief amid fears of climate change?
The bulbuls did do well over the last few decades thanks to the warming and the abundance of their food sources in or near human settlements, but they could be an exception to the norm. Many other species are facing the threat of extinction due to human activities.
Though we have not yet confirmed it in our study, there were studies in Japan warning that the bulbuls had become an invasive species in some northern regions and threatened some native species. In China, we have many people setting up nets and firing shotguns to kill migrating birds. The most recent hunting was widely reported by the media in Jiangxi and Hubei provinces last year. Most of the birds became food in restaurants.
The birds' natural habitats are disappearing rapidly, too, especially in coastal areas. Many shores where migrating birds typically stopped to rest and feed have been converted into beaches or real estate projects, causing the deaths of countless birds every year.
Air and water pollution also threaten the existence of many birds. Though there have not been much studies on the impact of PM2.5 on birds, I am quite sure that it would do harm. Birds are very smart. They limit their activities such as feeding and flying on smoggy days. But unlike humans, who can stay indoors or drive a car to avoid the smog, the birds have nowhere to hide.
Xing spoke with Stephen Chen