The beating of wings on Charles Darwin Reserve

Saturday 20 March, 2010

Ecological Outcomes Monitoring Coordinator, Jim Radford, looks back over the first four years of bird monitoring on Charles Darwin Reserve to reveal some interesting trends.

Salt lake, Charles Darwin Reserve. Photo Dale Fuller.

Salt lake, Charles Darwin Reserve. Photo Dale Fuller.

‘The unique location of Charles Darwin Reserve, at the junction of two major botanical provinces, is responsible for the extraordinary diversity of plants found there.

This diversity of plants and landscapes means that it also supports an abundance of birdlife. More than 100 bird species have been recorded so far. Several of these are threatened – such as the iconic malleefowl and Major Mitchell cockatoo – and many others are of conservation concern, including the Australian bustard, regent parrot, rufous treecreeper and white-browed babbler.

Bush Heritage purchased the reserve in 2003 and we've been monitoring bird populations each spring since 2005, as part of our long-term Ecological Outcomes Monitoring (EOM) program.

Regent Parot. Photo Dale Fuller.

Salt lake, Charles Darwin Reserve. Photo Dale Fuller.

There are now more than 80 permanent monitoring sites that are representative of the underlying variation in geology, soil type and topography. This monitoring effort, conducted with the help of Bush Heritage supporters and volunteers, provides powerful indicators of ecosystem health and is starting to pay dividends: several interesting trends are emerging that will inform future management.

Trends in species richness and abundance

We detected a 25% increase in total species richness (about two additional species per site) and a 45% increase in total abundance per site from 2005 to 2006 and 2007. However, both indicators had receded back to 2005 levels by 2008. This pattern was observed for most groups of birds except nectar-feeding birds, which remained high in 2008.

Interpreting these patterns is challenging. The initial increases (2005 to 2007) may be a result of removing stock and controlling feral animals (especially goats), leading to increased plant growth and availability of food resources such as insects, nectar, seeds and fruit. However, this appears to be only part of the story and doesn't explain the dip in 2008.

Rainfall is a key influence on wildlife, and there's often a lag between good rainfall and increases in bird populations. Rainfall at Charles Darwin Reserve was about average between 2004 and 2006, well below average in 2007 and slightly above average in 2008.

A cluster of Major Mitchell Cockatoos. Photo Dale Fuller.

A cluster of Major Mitchell cockatoos. Photo Dale Fuller.

The increases detected between 2005 and 2007 were probably a result of our changed land management regimes. However, the decline in many bird groups in 2008 may be a legacy of the very dry conditions in 2007, when breeding success would have been very low and some species may have sought better conditions elsewhere.

Why didn’t the nectar-feeding birds also decrease in 2008? Many nectar-feeding birds are highly mobile nomads that traverse the landscape in search of the best feeding patches. Their continued abundance in 2007–08 suggests that, while conditions may have deteriorated, the reserve still contained some of the best feeding areas in the region and was a refuge for birds during stressful times.

This demonstrates the importance of considering ecological changes on our reserves within a broader landscape context because species will move around the landscape in response to variations in resource availability. What happens on our reserves will be a product of our management but also of what’s happening elsewhere in the region.

The future

Understanding ecological systems and their response to management takes time and patience. The variation in the bird data shows the importance of annual monitoring and taking a long-term perspective so as not to become overly pessimistic or optimistic about year-to-year changes in particular species.

Real change may take decades to become apparent. After four years of monitoring, we're starting to build a picture of the ‘background’ variation due to rainfall and wider landscape factors, against which longer-term change can be compared.

As we continue to collect data, we'll be able to examine the influence of fire history, grazing management, feral herbivore control and other management interventions on the bird community, and integrate the results of monitoring into the management review process on Charles Darwin Reserve.

Bush Heritage’s Ecological Outcomes Monitoring program is generously supported by the Macquarie Group Foundation.

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