Hope Farm's summer monitoring blog 2024

Duerden Cormack, Monitoring Assistant at RSPB Hope Farm, summarises the key findings of the core monitoring of breeding birds, butterflies, and bumblebees carried out at Hope Farm during the summer months of 2024.

After last year’s changeable weather this year has at least been predictable - it was constantly cold and wet! Seemingly endless drizzly mornings made it difficult to plan surveys and I was concerned that I would undercount species like Skylark that sensibly hunker down in the rain. Besides frustrating fieldworkers and farmers, it will be clear later in this blog that the weather has caused issues for our wildlife.

An omission from this season’s report will be data on bumblebees. Towards the end of summer, I was seconded to cover vegetation surveys for an RSPB Conservation Science project. This and a lack of dry survey days meant I didn’t complete enough BeeWalk transects to give us an informative picture of the year. Thankfully though, our brilliant volunteer Rod stepped in to cover butterfly transects for the weeks I was away so I have a full year to present. Thank you, Rod!

To keep up to date with farm news and interesting wildlife sightings, you can find us on Twitter @RSPBHopeFarm.

Birds

To monitor breeding birds at Hope Farm we use the BTO’s Common Bird Census methodology. This entails 20 dawn starts between March and July to cover the entire 180ha farm 10 times. The behaviour and location of breeding species are recorded on visit maps which are then collated into individual maps for each species at the end of the season. This allows us to analyse the maps using the BTO CBC guidelines and calculate how many territories were held on the farm by each species. In 2024 we recorded territories for 15 of the 18 Hope Farm Breeding Bird Index species in contrast to the first surveys completed when the RSPB took on ownership of the farm when just 10 of the 18 index species were recorded (Table 1).

Eagle-eyed readers will notice that the usual Hope Farm index of 17 species (based on Defra’s 19 species index) has increased by one this year. After large numbers in winter, three pairs of Rooks stayed to nest for the first time this year.

Table 1. Territory numbers of Hope Farm Breeding Bird Index species

Using these counts we produce a Breeding Bird Index for the farm which gives a measure of the average change in the number of territories held by these 18 species. As of 2024 the Hope Farm Breeding Bird Index stands at 2.53 compared to the baseline of 1 set in 2000, equivalent to a 161% increase (Figure 1).

Figure 1: The Hope Farm Breeding Bird Index

This year has seen an increase in the index and brings us back in line with the apparent stable equilibrium that has emerged since 2009. It has been a joy to have three Corn Bunting territories on the farm this year, with one male singing next to a footpath almost daily throughout the summer. Grey Partridge also did well with six territories, though there were fewer than expected coveys this autumn which suggests low productivity in the wet weather. We were pleased to see that Whitethroat showed signs of a recovery compared to last year with five more territories recorded, and Linnet and Skylark also did well.

Picture 1: A recently fledged Kestrel (Duerden Cormack, Hope Farm 2024)

Outside of the index species however we have seen some worrying declines. Most striking is Chaffinch which has undergone a c.90% reduction in territory numbers in just six years. This has been linked to trichomonosis, a disease caused by the protozoan parasite Trichomonas gallinae and has contributed to a 41.9% decline in the national population since 2011. Infected, lethargic birds are often seen at garden bird feeding stations where the disease is spread. As well as Greenfinch, another casualty of this disease appears to be Bullfinch which has undergone a steep decline nationally since 2016. For the first time since we acquired Hope Farm, no Bullfinch territories were recorded this year (Figure 2).

Figure 2: Territory numbers of three finch species (Chaffinch, Greenfinch, Bullfinch) on Hope Farm.

Another cause for concern has been a decline in Blackbird territories. In 2023 we recorded just 23, down from an average of 33 since 2000. We speculated that this might have been caused by the drought and extreme heat in 2022 but rather than a recovery in this wetter year we recorded just 21 territories. If this apparent decline continues next year, then it might be that we are witnessing the spread of Usutu virus which was detected in British Blackbirds in London in 2020 and in Cambridgeshire in 2023. Usutu virus is spread by mosquitos and affects organs including the brain. Where it has been detected in Blackbird populations it has been associated with local declines (Figure 3).

Figure 3: Blackbird territory numbers on Hope Farm.

With this disease pressure in mind, we will be keeping a close eye on the rest of our farmland birds. For example, although they are known to struggle in wet weather, our buntings have performed poorly this year with 4 Reed Bunting territories (average 9 since 2000) and 19 Yellowhammer territories (average 27 since 2000). Could they too be suffering from Trichomonosis? Although garden bird feeding is largely blamed, farmers need to be cautious in our approach to supplementary feeding – piles of seed under hopper feeders or at winter feeding stations could become a site of disease transfer from finches and pigeons into other farmland species. We will be spreading our winter supplementary feed much more thinly this winter to avoid contamination from seed regurgitated by infected birds.

Picture 2: A Goldfinch nest (Duerden Cormack, Hope Farm 2024)

Butterflies

As usual, three UK Butterfly Monitoring Scheme transects were surveyed each week between 1st April and 30^th September. In total, 2680 butterflies of 25 species were recorded and submitted to Butterfly Conservation for their national monitoring efforts. The Hope Farm Butterfly Index now sits at 1.85 compared to the baseline of 1 set in 2001 – equivalent to a 348% average increase (Figure 4).

This is a decline on last year and mirrors the findings of other ecologists, naturalists, and transect walkers. Although it is often difficult to pinpoint the drivers of population trends, this year’s dramatic drop appears to have been caused by the wet weather. Gatekeepers and Meadow Browns were scarce for example: the maximum day count of Meadow Browns was 118 compared to 383 last year and for Gatekeepers the maximum day count was 140 compared to 315 last year. It seems likely that some of the cold, wet snaps in the early season coincided with critical periods during the larval and/or pupal stages of these species.

The “blues” also did badly, and this was our worst year ever for Small Tortoiseshell - just two were recorded on our transects all summer.  Early indications presented in the most recent UKBMS newsletter suggest it has been a very bad year for Small Tortoiseshell nationwide which is especially concerning for a widespread, generalist species. This species fared badly in 2023 so perhaps the weather exacerbated an ongoing decline.

In more positive news, this was the best year ever for Marbled White, Ringlet recovered slightly, and Small Heath continues its unstoppable, climate-induced increase - they will soon take over the world! As I am writing we are experiencing a very mild autumn and butterflies are still around in numbers, particularly Red Admirals feeding on Ivy but also the occasional Speckled Wood.

Picture 3: A pair of Gatekeepers (Marta, Hope Farm 2024)

Conclusion

In summary, this year has been better for some of our key farmland bird species, but disease and weather are putting significant pressure on our wildlife. Anecdotally, bees and groups such as hoverflies were often conspicuously absent but others such as beetles and true bugs appeared to fare better. As I seem to conclude every year, farmers and wildlife alike cannot escape the effects of climate change and the best we can do at the farm scale is to provide good quality habitats and adopt practises that will hopefully buffer against the challenging weather we are set to experience in years to come.