Liping Zhou & Eben Goodale
Linked paper: The response of mixed-species bird flocks to anthropogenic disturbance and elevational variation in southwest China by L. Zhou, I. Peabotuwage, H. Gu, D. Jiang, G. Hu, A. Jiang, C. Mammides, M. Zhang, R.-C. Quan, and E. Goodale, The Condor: Ornithological Applications.
Have you ever looked up at a mountaintop in the distance and wondered what birds might be living there? When mixed-species flocking fanatics like ourselves see that mountain, another set of questions catches our imagination. We wonder what the flocks are like up in that place: are they larger or smaller than what we’ve seen here? Are they led by the same species that leads the flocks down here? What do they sound like, how do they behave?
The Hengduan Mountains of southwest China are a good place for someone who likes these kinds of questions (and likes misty mountains!). Bordering the Himalayas to the east, this is one of the great bird diversity hotspots of the world. Because of the range of elevations here, within a relatively small area one can see many different kinds of biomes, from tropical rainforest at the southern edges to treeless alpine grassland. In the lowlands of south China, nearer the coast, one can find a flock system dominated and led by a super-species complex of songbirds called fulvettas (Alcippe hueti or A. davidi or A. morrisonia). We looked at the rolling mountains of northern Guangxi and the more substantial mountains in Yunnan and wondered, what’s up there?
We were also motivated by conservation-related questions. The past few decades have seen a paradigm shift in conservation, from focusing on single species to trying to protect and manage the webs of connections between species and the ecological processes that flow from them. Mixed-species flocks are a good example of sensitive species interactions that can be affected by human activities, with flocks sometimes changing their form even if all the constituent species are still present in an area. For our project, we looked at a range of land use types over the elevational gradient, from the primary forest (usually isolated now on the mountain tops), to degraded forest and timber plantations, to intensive agriculture (usually maize or wheat in this part of the world).
You’ll have to read our paper for all the details of what we found, but briefly (spoiler alert!) we did find a similar flock system to the south China coast, led by Alcippe yunnanensis and A. davidi. This system breaks down in intensive agriculture, with flocking “propensity” (the percentage of individuals in flocks) only about a third of what it is in forest. Flocks in buffer areas are more similar to forest, but with some substantial differences including lower propensity, a set of alternative leaders, and less complex interactions between species, as judged by social networks.
This kind of research always raises exciting new questions to chase next: how do these flocks compare to those in Sichuan to the north, or in the countries of Southeast Asia to the south? Flocks and the forest specialists in them clearly did not do well in seeded pine in the buffer areas in our study. What exact kind of vegetation (e.g. how degraded a degraded forest) can retain these flocks is an important next question, but even at this point we know enough to sketch the broad implications for conservation. At least at present, this system is more affected by land use change than climate change, and the flocks are most complex inside forests, emphasizing the value of the network of protected areas in the region. Those reserves and their proper management are essential for protecting an extensive avifauna (in all we saw 311 species, not including aerial specialists and raptors), especially forest specialists (we estimated 75 species fell in such a group), and this unique and fascinating flock system.
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