Historic changes in species composition for a globally unique bird community

High-integrity, sub-Himalayan forests of northern Myanmar give a unique insight into natural changes in bird diversity through time, with surprising results.

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To study changes in species diversity and species composition over time is difficult. It requires historical datasets that are sufficiently robust to be compared statistically with those from the present. To find such datasets in pristine forest, and in the subtropics, and for all these datasets to be at least 60 years apart, is extraordinary.

In this respect, the datasets for the birds of Hkakabo Razi are possibly unique. For this, we must thank our illustrious forebears, naturalists such as the Earl of Cranbrook, Bertram Smythies, Major John Stanford, Ronald Kaulback, and the botanist Francis Kingdon-Ward. Not only did they undertake arduous and epic field trips into the Hkakabo Razi forests, but also, crucially, they wrote meticulous specimen labels.

A black-naped monarch (Hypothymis azurea) feeding young; one of 450 bird species recorded from Hkakabo Razi, © Kyaw Myo Naing

What these accomplished naturalists noted, and what we have subsequently confirmed in a series of five major expeditions (2001 to 2016), is that the forests of Hkakabo Razi are one of the most biologically diverse places on earth. However, what has surprised us, is not a change in species richness over time - there has not been one - but rather a significant change in bird species composition. This is unexpected, at least the magnitude of change.

The author with U Myint Kyaw recording bird field data in Hkakabo Razi forest © Swen Renner

When we sampled sites adjacent to those of the past, we found, amazingly, that less than 20% of bird species occur in both time periods. Meanwhile, not one of the five most abundant species of today is the same as before. As humans, we tend to resist the idea of dynamism in natural systems, especially changes that we cannot readily explain. Our peers made helpful suggestions – must be something to do with the different methods of data collection, different seasons, different locations, increased human impact… but when we controlled for all of these, the same result – an extraordinary change in composition.

Pristine forests near to Tazungdam in Hkakabo Razi © Swen Renner

Is this important? We think it is, especially when we are trying to assess the impact of human-induced environmental change on natural systems. We cannot assume that all things being equal, natural systems remain constant, even in relatively short historical time periods.

A pair of rufous-necked hornbills (Aceros nipalensis) © Kyaw Myo Naing

So, we need to go back to these wonderful forests to try and tease out further patterns and idiosyncrasies amongst the 450 or so bird species known from the area. We will also need to help promote their conservation since ominous storm-clouds of threat are gathering on the horizon. These forests are too precious to lose. They are the meeting point of three biodiversity hotspots, three biogeographical regions, two ecozones and three endemic bird areas and include two IBAs. They are home to Southeast Asia’s highest mountain, Mount Hkakabo Razi at 5,881 metres, and to high plant species richness and endemism, including diverse medicinal plants and >100 species of orchid.

Some of the 2016 field team waiting for birds © Swen Renner

What have we learnt so far? Firstly, that if you want to live the adventures of trekking in these beautiful forests but prefer the comfort of the armchair to the rigours of climbing 50° slopes, battling leeches, and crossing numerous torrents on ridiculously flimsy rattan suspension bridges, then read the wonderful books of Kingdon-Ward, which provide keenly observed ecological information in a vivid prose style. Second, if you go on an expedition with five scientists, five guides, and 60 helpers, take more than one cook unless you want to eat plain rice, morning, noon, and night for almost six weeks!

Swaying rattan suspension bridges, like the one close to Gawlai in 2014, are found throughout Hkakabo Razi © Swen Renner

Swen Renner

Scientist, Natural History Museum Vienna

My research focus is on biodiversity and biogeography, particularly how ecosystem processes and species diversity are affected by global change.

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