Project Update: Monitoring winter water birds on the River Irwell
New report published reveals changes to water birds using the River Irwell
In 2018, Kersal Wetlands (28-hectare flood basin that lies within a meander of the River Irwell and includes 5 hectares of urban wetland habitat) was constructed as part of a flood protection scheme at the site of the old Manchester Racecourse. The new report uses winter wetland bird monitoring data to discover what change this significant new habitat has made to the bird populations of the River Irwell.
Natural Course and the Greater Manchester River Ecology Project set up a winter wetland bird monitoring project along the lower reaches of the River Irwell. The Winter Wetland Brid Blitz (WWBB) is a collaboration with the Wetland Bird Survey (WeBS)1. We are building up a valuable long term systematic and structured dataset by asking teams of volunteers to survey stretches of river on the same day each year, over several years, and combining it with similar historic data from WeBS. These characteristics are important if we are to use comparisons of the data to monitor for any changes in the birds using the river. This is particularly useful because birds are good indicators for the overall health of an ecosystem.
The original inspiration for starting the WWBB monitoring project in 2017 was to monitor the Irwell Site of Biological Importance (SBI). It had been cited for its regionally important number of wintering Goldeneye and Tufted Duck and anecdotally they were in decline. However, the SBI is reviewed periodically. So, in the meantime, because the WeBS and WWBB have been designed to produce comparable data, we can apply the outputs to other monitoring questions.
Hence, the team have been able to use data collected by the WWBB and WeBS to write a new report that compares recent results with results from similar surveys carried out in previous years at sections alongside, upstream, and downstream, of the recently constructed Kersal Wetlands.
- Sets out the background to the survey.
- Shows the location of Kersal Wetlands and the survey count sections.
- Gives a summary of the survey method.
- Explains the method used to compare survey results.
- Charts and describes the comparative figures of total bird count, total species count, and each species of waterbird where there was enough data to potentially show a trend.
- Lists limitations of the survey and comparison method.
- Discusses the comparative figures to see if any trends can be identified and assigned to the creation of the wetlands.
The study found that the counts for most species showed considerable variation between years without a discernible pattern. As an example, the total counts were 542 for 2018, 857 for 2019 (+58%) and then back down to 573 (-33%) in 2020 – the number of species showed a similar pattern.
However, there was a steep decline in Mute Swans between 2002 and 2009. Initially there was a total of 49 of these birds seen along the three count sections. By 2009 this was just 2, and no swans at all were seen during the subsequent surveys. This was before work started on the Kersal Wetlands but is still a concerning finding. Thankfully it is not reflected by the national population trend 2009-2019, where there has been a 9% reduction.
Another trend recognised by the report is the growth of Goosander seen between Agecroft Bridge to Ringley Road Bridge, from 5 in 2002 to 15 in 2020. This is good to see, but it is not adjacent to the new wetlands.
On the other hand, the significant increase in Canada Geese between Cromwell Bridge and Agecroft bridge is directly adjacent to the created habitat and coincides with its construction. The growth in population of 232% between 2009 and 2019 far exceeds the national trend of 100% for that period. The neighbouring two count sections saw no growth during this time, further indicating that the change is linked to the arrival of the wetlands.
Mike Beard, Natural Course Project Officer and Greater Manchester Environment Team says….
“This new study has shown the added value of structured surveys. While the comparable long-term dataset gathered by the volunteers will achieve the original purpose of monitoring the River Irwell SBI, it can also be applied to other questions as well or bring to light unexpected population trends.
For instance, the recent scarcity of Mute Swans along this section of river came as a unhappy surprise to me. Meanwhile, the increase of Canada Geese was suspected, and it is good to have proof that it has been exceptional even considering their very rapid growth nationally. Now that we know of the success and failure of these two species at this location we can consider if either outcome presents a problem, investigate the cause and any wider implications thereof, and what we could do about it.”
You can read the full report here: Winter-water-bird-monitoring-on-the-River-Irwell-adjacent-to-Kersal-Wetlands-Final.pdf (naturalcourse.co.uk)
- WeBS is a partnership scheme of the British Trust for Ornithology (BTO), the Royal Society for the Protection of Birds (RSPB) and the Joint Nature Conservation Committee (JNCC) (the last on behalf of the statutory nature conservation bodies: Natural England, Natural Resources Wales and Scottish Natural Heritage and the Department of Agriculture, Environment and Rural Affairs, Northern Ireland) in association with the Wildfowl & Wetlands Trust (WWT).