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www.nature.com/scientificreports OPEN Historic changes in species composition for a globally unique bird community Swen C. Renner 1,2* & Paul J. J. Bates 2,3 Signifcant uncertainties remain of how global change impacts on species richness, relative abundance and species composition. Recently, a discussion emerged on the importance of detecting and understanding long-term fuctuations in species composition and relative abundance and whether deterministic or non-deterministic factors can explain any temporal change. However, currently, one of the main impediments to providing answers to these questions is the relatively short time series of species diversity datasets. Many datasets are limited to 2 years and it is rare for a few decades of data to be available. In addition, long-term data typically has standardization issues from the past and/or the methods are not comparable. We address several of these uncertainties by investigating bird diversity in a globally important mountain ecosystem of the Hkakabo Razi Landscape in northern Myanmar. The study compares bird communities in two periods (pre-1940: 1900–1939 vs. post-2000: 2001–2006). Land-cover classes have been included to provide understanding of their potential role as drivers. While species richness did not change, species composition and relative abundance difered, indicating a signifcant species turn over and hence temporal change. Only 19.2% of bird species occurred during both periods. Land-cover model predictors explained part of the species richness variability but not relative abundance nor species composition changes. The temporal change is likely caused by minimal methodological diferences and partially by land-cover. Species richness, relative abundance and species composition are dynamic phenomena and vary in space and over time1,2. Recorded fuctuations of bird species richness and species diversity are explained by deterministic changes (e.g., global change such as changes in land-cover or land-use intensifcation1), methodological changes (diferent efort or sites; limited or no standardisation; and methodological and non-systematic errors 3,4), random processes (e.g., neutral dynamics 5–8), or any combination of the above. Global change is rapidly proceeding and includes land-use intensifcation, changes in land-cover, climate, atmospheric composition, and invasive species, among other factors1. Land-cover change is probably the most important in terms of species response 9,10. It is probably more important than climate change for most biodiversity1,11, particularly for many bird species9. Land-cover change, including land-use intensifcation, have been shown to afect species in a variety of direct, indirect and interacting ways, including local extinction, range shifs, changes in local abundance, or interactions with other species 12–14. Although several studies have shown the efects of global change in the form of habitat loss or land-use change, these studies typically are limited in explanatory power. In many cases, the historic (previous) baseline, which is used to estimate the diversity statistics, has a low statistical power. In others, the temporal aspect is too short to show meaningful efects15. Most studies use only recent baseline data and the time diference (mostly 2 years, in rare instances more than a decade) is too short for changes in species assemblage. Typically they explain only short-term fuctuations, particularly fuctuations within or between consecutive years7,16,17. Only a few regions worldwide remain with a habitat cover of near pristine condition15. Tese untouched areas are embedded in a land-cover mosaic of various forms 18. Te Hkakabo Razi Landscape in the northern tip of Myanmar is largely untouched and includes large tracts (11,280 km2) of pristine forests interspersed with a few, relatively small areas of degraded forests or other local land-cover forms 19. Within this Landscape, an historic bird assemblage has been documented20. Tese baseline data were collected by British and US explorers and include specimens and letters on methods and localities. It is the quality of this historical documentation, together with 1Ornithology, Natural History Museum Vienna, Burgring 7, 1010 Vienna, Austria. 2Institute of Zoology, University of Natural Resources and Life Science, Gregor-Mendel-Straße 33/I, 1180 Vienna, Austria. 3Harrison Institute, Bowerwood House, 15, St Botolph’s Road, Sevenoaks, Kent TN13 3AQ, UK. *email: [email protected] SCIENTIFIC REPORTS | (2020) 10:10739 | https://doi.org/10.1038/s41598-020-67400-z 1 Vol.:(0123456789) www.nature.com/scientificreports/ the rigour of the collecting methodology (which compare favourably and complement the recent eforts), that makes the Hkakabo Razi Landscape almost unique for studying species compositional turnover. At the same time, the efects of land-cover change on birds can be analysed, because the historic samples are located in pris- tine forests, while our own recent samples cover both pristine and some of the relatively few degraded habitats. Te historic and recent collections, when reviewed together, allow for an analysis of the historical changes to bird assemblages, covering data separated by almost 70 years. Tis will increase our understanding of temporal dynamics in bird communities. Mountain ecosystems of the tropics are home to high species diversity. Tose of the Himalayas, including the Hkakabo Razi Landscape are also home to a rich variety of endemic taxa. For example, the study area hosts at least one endemic bird (Jabouilleia naungmungensis21) and at least two endemic subspecies of birds20,22 (Alcippe cinereiceps hkakaboraziensis, Malacocincla abbotti kachinensis; all species and samples are listed in Online Sup- porting Information Table S1). However, all biodiversity in mountain ecosystems is vulnerable to land-cover change23. Currently, the forests of the Hkakabo Razi Landscape are likely the last vast area of pristine forests in Asia or at least Southeast Asia 19,24–26, with relatively few degraded habitats imbedded within the pristine forests. To date, 456 bird species have been recorded in the Hkakabo Razi Landscape, proving its global importance for bird conservation. While the Hkakabo Razi Landscape covers about 1% of terrestrial Myanmar, it is habitat for almost half of all bird species recorded from the country (456 vs. ~ 1,10020). Here we describe and test species turnover and temporal variation in relation to global change parameters. We predict no detectable diferences in species richness, relative abundance or species composition between the two periods considered (pre-1940 vs. post-2000), because land-cover change has not yet occurred to a signif- cant extent. In turn, any signifcant diferences in species richness, relative abundance or species composition would indicate a high proportion of temporal variation (i.e. non-static species composition) and/or a response to deterministic reasons (e.g., environmental drivers). If we fnd a diferences in species composition between the two periods of over 50% (natural fuctuations in bird communities of the tropics with very limited human impact exhibit up to 49% species change within or between years27), or signifcant variation between the periods in respect to species richness and relative abundance, these fuctuations can be interpreted as a consequence of temporal change. Since the Hkakabo Razi Landscape is one of the few remaining signifcantly large and natural mountain forests worldwide24–26,28, from which we have almost perfect historical datasets, it is an invaluable natural laboratory in which to test the impact of temporal change on species richness, relative abundance and species composition. Te results of such studies are of global importance. Te Hkakabo Razi Landscape is a unique constellation of largely “untouched” forests26 with collectors in the frst half of the twentieth century having labelled their specimens almost perfectly. Material and methods Study region and study sites. Te study sites, i.e. the localities of bird sampling, are located in the Hkak- abo Razi Landscape. Distribution of the localities and consequently the area covered is defned by the historic collectors (redrawn in Fig. 1, following Suarez-Rubio, et al.26). Te Hkakabo Razi Landscape is located in the northern most part of Myanmar (to many Westerners still known as “Burma”) and comprises the Hkakabo Razi National Park, the planned “Southern Extension” of the National Park and the Hponkan Razi Wildlife Sanctuary (all borders as proposed on August 15, 2015). Within the Hkakabo Razi Landscape, two major survey programmes have been completed to assess the total number of species. Te frst, a series of uncoordinated ‘one-of’ studies was undertaken by British collectors in the early twentieth century, the second by S.C.R. and several colleagues in the early 2000s20. All samples are available, either at the Natural History Museum (Tring, UK), or at the Smithsonian Institution (Washington, DC, USA) or at the Zoological Park (Yangon, Myanmar). In the post-2000 studies, all samples were taken in accordance with European Union, US and particularly national Myanmar laws on animal protection and conservation measures at the time of data sampling. All nec- essary permits have been approved by the Nature and Wildlife Conservation Division of Myanmar’s Ministry of Natural Resources and Environmental Protection (MoNREC, formerly Ministry of Forestry—MoF). Te responsible ofcers and the permit number are listed in the acknowledgements.

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