Rainfall changes have affected the distribution of the Magpie-lark (Grallina cyanoleuca) in Western Australia

Transcription

1 Cygnus (2012) 1: DOI , , , RESEARCH ARTICLE Rainfall changes have affected the distribution of the Magpie-lark (Grallina cyanoleuca) in Western Australia Kate Stanbury Mark Dutton Alison Liew Bethany Cooper Received: 23 May 2012 / Accepted: 30 May 2012 Abstract The purpose of this study was to assess whether the distribution of Magpie-larks (Grallina cyanoleuca) in Western Australia have been affected by changes in the rainfall patterns experienced in Western Australia. In order to show this, distribution maps of the Magpie-lark were compared to rainfall pattern maps. Analysis of these maps indicated that the distribution of the Magpie-lark has changed and increased in areas where there has been increased rainfall. Furthermore, the scale of the projected changes to rainfall patterns in Western Australia in the next 100 years might well result in the distribution of the Magpielark diminishing in some areas whilst rising in others. A complicating factor not addressed by this study is the ability of the Magpie-lark to adapt to urban conditions which itself might result in distribution changes separate to rainfall. Citizen collected data has been used in this study, taken from ClimateWatch and The Atlas of Living Australia. Such data has limitations, with little data available prior to 1950 and the ClimateWatch data coming from a different observer set and location than the Atlas. However it can be increasingly powerful in providing mass data. In particular the advance of technology is facilitating the input of such data into online databases by the general public. Hence citizen data had merit for this study and, the authors believe, more generally for the scientific community. Examination of the prepared maps shows that the original hypothesis about a correlation being present is supported, with the final conclusion being that the distribution of the Magpie-lark in Western Australia has increased in regions where there has been an increase in rainfall. Keywords Magpie-lark, Grallina cyanoleuca, phenology, climate change, distribution, Western Australia, rainfall 154

2 1 Introduction Climate change is a phenomenon that is currently affecting species all over the globe. With rises in global temperatures (Hurlbert et al. 2012), and changes in rainfall patterns prevalent, the distribution of species is changing (Fitzpatrick et al 2008). For Western Australia in particular, climate change is affecting the species that live in this region (Climate Commission 2011). Due to climate change, rainfall in Western Australia has become highly variable in the last 60 years and is impacting greatly on species distribution (Hughes 2003). Changes in local climate such as rainfall changes have been linked to changes in the timing of migration for avain species (Chambers 2008), as well as changes in other phenological traits such as breeding and hatching seasons and species distribution (Penuelas et al 2001). One species whose phenological traits are potentially sensitive to climate change is the Magpie-lark (Grallina cyanoleuca). Magpie-larks require fresh surface water for their breeding cycle to occur, and feed around freshwater swamps, lakes and streams (Robinson 1947b). There is evidence to suggest that during periods of unusally high rainfall, Magpielarks are capable of having extra broods and, if the environment is suitable, they are capable of a phenomenal increase in numbers (Robinson 1947b). Hence, with the Magpie-lark s dependence on freshwater availablity for life cycle events to occur, it could be expected that the distribution of Magpie-larks would change in response to changing rainfall patterns. This study uses citizen-collected data. The use of citizen science projects to obtain data for scientic analysis is not a new concept. In fact, Australian citizen scientists provided British naturalist John Gould with many of the specimens illustrated in his 1848 The Birds of Australia series (Lyons 2010). With the rise of the internet, the general public have been able to input their observations of species into online databases such as ClimateWatch and The Atlas of Living Australia. This has resulted in a plethora of data collected over many years about species in Australia. The online database ClimateWatch lists the Magpie-lark as one of its indicator species a species whose life cycle events are influenced by seasonal and interannual variations in climate (ClimateWatch 2012). Currently, there is very little knowledge about how rainfall patterns impact on the distribution of Magpie-larks. This article presents a study of the distribution of Magpie-larks in Western Australia over the last 60 years and compares that to the rainfall patterns over the same period in Western Australia. By examining citizen data taken from ClimateWatch and The Atlas of Living Australia, this paper hypothesize s that the rainfall patterns in Western Australia affect the distribution of Magpie-larks in Western Australia and that there should hence be a correlation between the species distribution and the rainfall patterns. 155

3 2 Materials and Methods In order to determine if a correlation between the distribution of Magpie-larks in Western Australia and the rainfall patterns of Western Australia exists, data relating to the distribution of Magpie-larks in Western Australia must be obtained, as well as the corresponding rainfall pattern data from Western Australia during the same period. The online databases ClimateWatch and The Atlas of Living Australia have extensive data available relating to the Magpie-lark and they were utilised for this study. In order to determine if a correlation exists, the distribution of the Magpie-larks from 1890 through to early 2012 was first mapped by using the latitude and longitude of sightings of Magpie-larks recorded in Western Australia. Once the latitude and longitude of the sightings recorded on ClimateWatch and The Atlas of Living Australia were known, these points were plotted onto maps, in accordance with the time period of each map. Outlier observations were checked for in the mapping process. Originally, the time periods to be examined were every 10 years from 1890 onwards, but there was insufficient data prior to Hence, the focus was narrowed to the most recent 60 years where there were sufficient sightings, plus an observable change in rain patterns. Mapping the locations of sightings of Magpie-larks was done on The Atlas of Living Australia s Spatial Portal. Once importation of the geographic points into the portal had occurred, a map of Western Australia was then generated that showed these points as a layer on the map. This process of importing the geographic points onto the Spatial Portal was followed to generate a map of the sightings from 1951 to 1970, then from 1991 to 2000 and then in the more recent period 2009 to 2012 the Atlas data was combined with Climatewatch data to generate the third and final distribution map. This simple mapping technique was judged adequate as the aim of the study was to determine if a correlation exists between the distribution of Magpie-larks in Western Australia, and the rainfall patterns experienced by Western Australia, and was not to assess density or bird populations. To generate maps of the rainfall patterns in Western Australia during the same time periods as the distribution maps, the search facility was used on the Australian Bureau of Meterology website. Maps of the annual average rainfall for Western Australia were then taken from the database that corresponded to the time periods used for the distribution maps. Projected rainfall pattern maps for Western Australia were also taken from the Australian Bureau of Meterology database to consider how the future distribution of the species might be impacted. Comparison of the distribution maps of the Magpie-larks and the rainfall patterns for Western Australia then allowed a judgement to be made about whether or not a correlation existed. 156

4 3 Results After examining the data and the prepared maps, it was concluded that there is a correlation between the change in distribution of the Magpie-lark in Western Australia, and the changed rainfall patterns that Western Australia has experienced over the last 60 years. Fig. 1 shows the rainfall patterns in Western Australia for (map a) and (map b). The inscribed circles on Fig. 1 show the regions that have received more rainfall in the period when compared to the same regions between Fig. 1 Comparative average annual rainfall maps of Western Australia. Map (a) is for the time period , showing the average annual rainfall in millimetres. Map (b) is for the time period , also showing the average annual rainfall in millimetres. Note the inscribed ovals on both maps which show significant increases in the amount of rainfall received in the circled areas. Fig. 2 shows the location of sightings of the Magpie-lark in Western Australia from 1950 to 1970 (map a) and 1990 to 2000 (map b). The inscribed circles on Fig. 2 map (b) show the regions of Western Australia where the Magpie-lark s distribution has increased between 1990 and 2000 when compared to the earlier period. A comparison of the areas of increased rainfall in the more recent period to 2000 as compared to the period to 1970 (highlighted by the inscribed circles in Fig. 1) with the increased area of sightings of the Magpie-lark in the period to 2000 as compared to 1970 (also highlighted by inscribed circles on Fig. 2), shows a clear correlation between the two areas of increase. Where rainfall has increased, the distribution of the Magpie-lark has also increased. However, as discussed below it does also show increased distribution where the rainfall has only marginally increased and that the distribution is steady where the rainfall has decreased. 157

5 Fig. 2 Comparative sightings maps of the Magpie-lark in Western Australia. Map (a) shows the location of sightings of the Magpie-lark from , with each circle representing one sighting. Map (b) shows the location of sightings of the Magpie-lark from , with each circle representing one sighting. Note the inscribed ovals on both maps. These ovals show the areas in which the Magpie-lark was sighted in the second period but not in the first period, indicating an increase in the distribution of the Magpie-lark. The more recent ClimateWatch distribution data from 2009 to early 2012 (Fig. 3) and future rainfall projections (Fig. 4) were also considered. Although the distribution data presented in Fig. 3 is limited compared to the earlier periods, it appears that the Magpie-larks have continued to exist in the same areas as they had in There is insufficient data however to conclude whether this supports or undermines the earlier correlation. When the projected rainfall patterns for Western Australia (Fig. 4) are considered, the average annual rainfall for Western Australia is set to decrease in some areas by up to 20% and increase slightly in others. Hence further changes in the distribution of the species are anticipated. 158

6 Fig. 3 Sightings of the Magpie-lark taken from the ClimateWatch data set, with sightings recorded from 2009 through to 2012 (ClimateWatch 2012) Fig. 4 Projected rainfall for Western Australia, taken from the 50 th percentile (the midpoint for the spread of the modelling results) relative to the 1990 baseline. It shows that for the entirety of Western Australia, rainfall is expected to decrease up to 20% in some areas, depending on the level of emissions expelled. 4 Discussion From the results above it can be seen that there is a correlation between the distribution of the Magpie-lark in Western Australia (Fig. 2) and the rainfall patterns of Western Australia (Fig. 1). With the Magpie-lark dependent on fresh water for its life cycle (Robinson 1947b) it is perhaps not surprising to see such a correlation. However it appears that there are other factors, perhaps more significant, that are influencing the distribution of the species. For instance it was noted that in areas where rainfall has declined the distribution did not appear to have declined in the periods reviewed. A contributing factor in the distribution of the Magpie-lark may be the availability of fresh water from human sources, such as human-made lakes, and watering holes for cattle. Magpielarks adapt readily to living alongside humans and are reknowned as one of Australia s most successful native avian urban adaptors (Kitchen et al 2010). 159

7 Hence when the rainfall projections for Western Australia are considered (Fig. 4) then this might lead to a scenario where the Magpie-larks overall distribution and even population grows rather than declines with overall decreased rainfall. If there are no other limiting factors then in the less urbanised northern region where rainfall is projected to rise the birds can more readily breed. Whereas in the south, given the greater human population and the bird s capacity to live in urban areas, they can benefit from access to human water supplies and so be somewhat insulated if the projected lower rainfall levels materialise. Another factor that may influence the distribution of Magpie-larks is the habitat which is available for residence as the heavy forest has been cleared and land cultivated, so has the Magpie-Lark extended its distribution (Robinson 1947a). Follow up studies that compare the species distribution changes to changes in land use and human activities should be conducted. Statistical analysis of the correlation of distribution changes with land use, rainfall and human population would provide deeper insights into the primary factors that are driving the distribution change of the species. The data that has been analysed must also be considered carefully. The distribution data is predominantly citizen-sourced. This means that care had to be taken when preparing the data for analysis as any unusal sightings recorded in the databases may have been a false sighting. In addition, when working with raw citizen data, a certain degree of precaution must be taken. As the data is coming from the general public there is no way of determining if the data is factually correct. Both the ClimateWatch and Atlas of Living Australia databases have procedures in place to limit the amount of false sightings that are recorded in their data sets. Further this study was assessing a simple variable (ie presence or not of a recognisable bird) hence the risk of incorrect data undermining the study s conclusions is relatively low. It must also be noted that the availability of data is limited and the observer base and location may be varying over time. In particular the more recent ClimateWatch data that was accessed (Fig. 3) only had the last three years of data available, whereas The Atlas of Living Australia had data available from However, even though there is data available from 1887 with an apparent broad distribution of the species, the number of observations in earlier years is low, which is most likely due to a lower number of recordings as opposed to less birds present. Hence, the interpretations may be skewed by a greater number of observers in recent times from a broader range of locations. This might be partly addressed over time by greater citizen participation in recordings. It would be beneficial if the citizens participating came from both urban and regional populations. Educational centres could be utilised as a natural, and relatively low-cost method to extend the number and location of observers. In addition, when entering a record of a species, the postcode of the observer should be provided to allow a greater understanding of the location of the observer. With knowledge of these variables, it would have been possible to map the observer population to see if the observer s location generated the apparent distribution change, rather than the change being simply due to the birds distribution change. This links with the debated topic of citizen science and its worth in the scientific field. The data that was used in this study has come from citizen science resources, with the findings 160

8 based on such data to a large degree. In essence, it is citizen science that has allowed this study to take place, and accepting the above limitations and risks with such data, citizen science does have merit for the scientific field. It allows commited and interested individuals to contribute to the scientific field on a regular basis. This is particularly the case for recognisable species as the risk of incorrect data is much lower than for harder to identify species, or where judgement is required on what type of behaviour is being exhibited In summary, conducting this study has increased the amount of knowledge that is available about the impact of changing rainfall on the distribution of Magpie-larks in Western Australia. Citizen science data was necessary to conduct this analysis and broadening citizen participation and data captured upon entry would facilitate future studies. The distribution of Magpie-larks has increased (Fig. 2) and that appears to be caused, in part, by changes in the rainfall patterns in Western Australia (Fig. 1). The distribution might increase further given the projected continuing changes to Western Australia s rainfall pattern (Fig. 4). However, there are believed to be other contributing factors and it is not possible from this study to conclude on the relative importance of the various factors. Aside from conducting similar studies in other Australian states, it is also recommended that studies comparing the observed distribution changes with changes in land use and human activities be carried out to better understand the effects of rainfall changes on the species distribution. Acknowledgements We would like to thank Birds Australia Western Australia Group for their advice and the following organisations for allowing us access to the data that has been examined throughout this study: ClimateWatch an initiative of the Earthwatch Institute of Australia; The Atlas of Living Australia an initiative of the Australian Government; and the Bureau of Meteorology - part of the Australian Government. In addition, we would like to thank peer reviewers: Zoe Bennett, Lisamarie Giancola-Bell, Samuel Charles, Julie Nguyen and sub editor Audrey Appudurai, for their valuable contributions in refining this manuscript. References Atlas of Living Australia (2012) Spaital Portal. Accessed 17/05/2012 Atlas of Living Australia (2012) Occurrence Records. 9a25-a54d6a345ceb#recordsView. Accessed 17/05/2012 Bereau of Meterology (2012) Chambers LE (2008) Trends in timing of migration of south-western Australian birds and their relationship to climate. Emu 108: 1-14 Climate Commision (2011) The Critical Decade: Western Australian climate change impacts p.8. [accessed 19/04/2012] ClimateWatch (2012) Fitzpatrick MC, Gove AD, Sanders NJ, Dunn RR (2008) Climate Change, plant migration, and range collapse in a global biodiversity hotspot: the Banksia (Proteaceae) of Western Australia. Global Change Biology 14: 1-16 Hughes L (2003) Climate Change and Australia: Trends, projections and impacts. Austral Ecology 28 (4): Hurlbert AH, Liang Z (2012) Spatiotemporal Variation in Avain Migration Phenology: Citizen Science Reveals Effects of Climate Change. PLoS ONE 7(2) Kitchen K, Lill A, Price M (2010) Tolerance of Human Disturbance by Urban Magpie-larks. Australian Field Ornithology 27:

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