Hope Farm Summer Monitoring Results 2023

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 2023.

This year will be memorable for me as my first year of surveying at Hope Farm. Starting in this role in January it has been great to watch the farm come alive as the seasons have progressed and it has been a real treat to get to know the patch and to watch birds like Yellowhammers and Grey Partridge on such a regular basis. Thankfully we did not have a repeat of last year’s extreme weather, but it was a very variable year with an exceptionally hot and dry June followed by a wet and cold July. In this blog I will focus on our findings from the core monitoring of breeding birds, butterflies, and bumblebees. For a full account of the farming year, click here to read farm manager Georgie Bray’s blog (after you have read mine of course!).

To keep up to date with farm news and interesting wildlife sightings, you can now find us on Twitter (now X) @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 2023 we recorded territories for 15 of the 17 Hope Farm Breeding Bird Index species which stands in stark contrast to the first surveys completed when the RSPB took on ownership of the farm when just 10 of the 17 index species were recorded (Table 1).

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 17 species. As of 2023 the Hope Farm Breeding Bird Index stands at 2.12 compared to the baseline of 1 set in 2000, equivalent to a 162% increase (Figure 1).

Figure 1: The Hope Farm Breeding Bird Index

This year has seen a decrease in the index with most of the indicator species at the low end of average compared to the last 10-15 years. As suggested in the 2022 summer monitoring blog, environmental impacts on breeding productivity are not often noticeable until the following year, in which case we may be witnessing the delayed effects of the extreme weather we experienced in 2022. For example, the larval and adult stages of craneflies (Tipuloidea) are an important component in the diets of Starlings (which fared badly this year), but these are known to suffer in droughts and heatwaves when otherwise damp soils are baked dry. A proportion of the craneflies that our breeding Starlings would have eaten and fed to their chicks in 2023 may have already perished in 2022 when they would have been young larvae and vulnerable to desiccation.

Whitethroat is another species that fared badly this year. We might speculate that this was also a result of last year’s weather but as always in ecology there as several alternative explanations. For example, there has been an apparent short-term decline in this species on the farm in the last 5-10 years. It is possible that this coincides with the rotational management of our hedgerows, some of which may be becoming unfavourably overgrown and lacking in ecotone (the interface where thorny hedgerow shrubs mingle with the grassy hedge base). On the other hand, the trend we have observed on the farm is similar to the national trend reported by the BTO (Figures 2 and 3). Determining the factors behind population trends in migratory species such as Whitethroat is especially tricky when conditions en route to and from and at wintering grounds are likely to play a part.

Figure 2: Whitethroat territories at Hope Farm 2000-2023.

Figure 3: Whitethroat population abundance in the UK. Harris, S.J., Massimino, D., Balmer, D.E., Kelly, L., Noble, D.G., Pearce-Higgins, J.W., Woodcock, P., Wotton, S. & Gillings, S. (2022) The Breeding Bird Survey 2021. BTO Research Report 745. British Trust for Ornithology, Thetford.

In more positive news, Corn Buntings held territory on the farm again, the relocated Lapwing plot attracted two pairs, and we had the first Jay territories for several years (including successful breeding!). The index still stands way above baseline and, given the pattern of stable equilibrium we have experienced over the last 10-15 years, we hope to see populations bounce back in years to come. Long-term monitoring will of course continue and in future we hope to undertake more in-depth analyses on the drivers of these trends.

Picture 1: A Whitethroat feeding two fledglings (Duerden Cormack, Hope Farm 2023).

Butterflies

For the 22^nd year, three UK Butterfly Monitoring Scheme transects were surveyed each week between 1^st April and 23^rd September. In total, 5576 butterflies of 25 species were recorded and submitted to Butterfly Conservation for their national monitoring efforts. This year we have updated our indexing methods and made the switch from the old Transect Walker indices to the new UKBMS estimates (UKBMS provides estimated totals for each species on surveys missed due to poor weather, illness etc.). These new estimates are slightly more optimistic and thus the index and percentage changes are higher than reported in previous years but otherwise the pattern remains unchanged.

The Hope Farm Butterfly Index now sits at 3.13 compared to the baseline of 1 in 2001 – equivalent to a 589% average increase (Figure 4). This represents a slight decline compared to 2022 but masks the fortunes of different species. Ringlet performed especially badly, just a handful were seen on the farm this year compared to several hundred just a few years ago. This species requires fine-leaved grasses in damper areas than other “browns” and is known to be badly affected by drought. It has certainly been damper this summer, so we hope to see some population recovery in this species next year. In contrast, Small Heath enjoyed another good year and continues to increase on the farm. It appears to have established a firm foothold here and has reportedly had a good year elsewhere in southern England. Could Small Heath be a climate change “winner”?

Figure 4: The Hope Farm Butterfly Index.

Bees

On the face of it, the results of our BeeWalk surveys show another worrying trend (Figure 5). Again, there has likely been some impact of last year’s extreme weather. Bumblebee Conservation trust report that in 2022 numbers dropped off strongly in late summer – nationally, BeeWalk data reveal the 4^th lowest July count ever and the lowest August count ever. They suggest that late-flying species may have been particularly badly affected as July and August are the peak months for worker recruitment and the production of males and new queens. It will be interesting to read the next annual report to see if this has carried over into population level effects in 2023, as it may have done on the farm.

At the local scale however, BeeWalk surveys give a better indication of bumblebee foraging activity than population levels. With this in mind, another possible explanation for our low numbers could be our cropping regime. Last year’s dry autumn prevented us from successfully establishing an Oilseed Rape crop and our Spring Beans also failed to get established. We were left just growing cereals while our neighbours grew lots of Winter Beans. This abundant supply of foraging opportunities just over our boundary could have drawn locally nesting bumblebees away from our transect route and exaggerated the apparent decline in numbers.

Figure 5: The number of bumblebees seen per 100m of transect.

Conclusion

To sum up, 2023 has been a challenging year for wildlife on the farm. The weather this year was very varied but has hopefully been forgiving enough to give our wildlife populations some respite and time to recover. We strive to provide good quality, well-connected habitats on the farm in the hopes that they will aid population recovery; but as this season goes to show, there is no escaping the broader effects of climate change and there is only so much that local action can achieve.

We’re now gearing up for our winter bird counts and are already seeing good numbers of finches and other passerines using our winter bird seed mixes. Keep an eye out for our winter monitoring blog and in the meantime keep up with us on Twitter (X) @RSPBHopeFarm.

Picture 2: A mating pair of Early Bumblebees (Bombus pratorum) (Duerden Cormack, 2023).