How Climate Change Changes the Distribution of Common Blackbird over Time

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Although the atmospheric temperature rises inconsistently, the trend of warming in Australia is still evident (PIRSA, Primary Industry and Regions SA). Figure 2 shows how the mean temperature of Australia has been changing from 1910.

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Figure 2. Linear trends in annual mean Australia temperatures since 1910 (left) and 1950 (right). Units are °C per decade.

From Figure 3, we can see that how the records from 1900 to 2006 experienced a trend of increasing rainfall over time. However, at South Australia, the amount of rainfall has been decreasing from the last 50 years; this can be seen in Figure 4 (BOM 2013). From 1997 to 2009, virtually the entire South East Australia experienced rainfall below the long-term average, with some places recording the lowest total on record (Climate Change Science 2011).

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Figure 3. Trends in annual rainfall during (a) 1900 to 2009 and (b) 1950 to 2009. Rainfall changes since 1950 have been significant in many years. Units are mm/ decade (BOM 2013)

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Figure 4. Mean annual rainfall over mainland south-eastern Australia from 1900-2005. Also shown is the 11-year running mean (solid black) (Timbal et.al,.2010).

I realised that there is a significant change in the distribution of T.Merula over the last decade. Figure 5,6 and 7 shows the distribution of the species (red dots represents the sighting records) in every 18-20 year interval (where the data sets have been imported to Atlas of Living Australia for mapping anlysis) dated back to year 1893.

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Figure 5. Distribution of T.Merula from 1893 to 1914 (left) and 1915 to 1934 (right).

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Figure 6. Distribution of T.Merula from 1935 to 1954 (left) and 1955 to 1974 (right).

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Figure 7. Distribution if T.Merula from 1975 to 1994 (left) and 1995 to 2013 (right)

Discussion

Large number of data sets from Atlas of Living Australia provides a great insight into the bio geographical response to the climate change, although the reliability of citizen science is often questioned. However, the huge number of sightings has provided certain degree of reliability in which the data can be used to analyse for research.

The sighting records show that there is a significant increase of number of Common Blackbirds in Australia, especially in southern-east area. It is obvious that the distribution is expanding towards North. Besides that, the population density has a gradual increase in the area where it has higher annual precipitation (Figure3). Evidence is marginal, however it holds a level of possibility which indicates a higher level of rainfall will be a favourable climate for T.Merula. The main diet of Common Blackbirds includes earthworm, where most of them only emerge after a rainfall, therefore a place with plenty of rainfall will be helpful for the birds to prey for earthworms. Also, sufficient rainfall helps the trees to grow quicker—some trees that produces fruits which are part of their diet. From here, we can see that the level of rainfall have a relationship with the abundance of food, thus affects the distribution of T.Merula.

The study results imply that the species T.Merula tends to favour cooler climates and areas where rainfall is more abundant. For temperature, it does not show a strong trend on how it affects the distribution of the species. However, they tend to stay at the southern-east Australia rather than other area. For example there are less sightings recorded at the middle area of Queensland and Western Australia; the Common Blackbirds mainly distribute at the New South Wales and South Australia (please refer Figure 2 as well as 5, 6 and 7 to compare).If I do a detail observation, the species has once appear in Queensland during the time range of year 1955 to 1974; after a period of disappearance, they appeared during the recent time which is 1995 onwards till present. Even though the species came back to Queensland, they have actually shifted to different location of Queensland where the temperature is slightly lower than the previous occurrence area. It might due to how the temperature at certain areas is too high or too low for them to breed etc. Overall, the results have supported my hypothesis (although the evidence is not strong enough)—the climate change in Australia has affected the distribution of the species T.Merula over time.

One limitation for my research will be the existence of other factors that could possibly affect the distribution of T.Merula, as my research is based on only the relationship between the climate and the species. There will be other factors such as the abundance of food, predation by other species etc., which can alter the distribution of Common Blackbirds. Those other factors are not within the scope of my research so they are not included in the data, thus the result would not be 100% accurate.

The other limitation will be the reliability of citizen science. The records are very limited as they are only based on the volunteer participants for the program. Those volunteers may not have much knowledge on the particular species or in biology, so it can make a difference in the result from database. Besides that, the record can be influenced by population density of people as well as the occurrence location of the specific species. For example some of the species habitats in remote areas where there are less people, thus less or no sightings will be recorded even though that specific species can be found at that place.

In conclusion, I think that the records from the findings can only remain as a reference for further research, it is not suitable for treating it as a research base to be further justified as the accuracy of the records are extremely questionable due to numerous factors that can alter the results. Therefore further studies are required improvement.

Acknowledgements

I thank Halina Top and my demonstrator, Audrey Appudurai for guiding me through the entire research. I also acknowledge Atlas Living of Australia, Climate Watch and Australia Bureau of Meteorology.

References

Atlas of Living Australia (2013) Available from: . Accessed 12 April 2013

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