Bilberry bumblebee

Overall vulnerability

Feature(s) assessed:

• Bilberry bumblebee (Bombus monticola)

Special qualities:

• Internationally important and locally distinctive wildlife and habitats

Feature description:

The bilberry bumblebee is a distinctive native bee that has a rich orange colour over two thirds of its abdomen. It is found in moorlands areas where bilberry is abundant and where it has access to grassland habitats for other flowering plants such as clover, marsh thistle, and bird’s-foot trefoil. A cold-adapted insect, it is one of Britain’s rarest bumblebees and in decline across the UK. A locally distinct moorland species, PDNP bilberry bumblebees are on the southern edge of records in England and are found right across the area where habitat is suitable. An exact PDNP population estimate is unknown due to difficulties in recording and quantifying bumblebee populations.

How vulnerable are bilberry bumblebees?

Bilberry bumblebees in the PDNP have been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, coupled with an unclear but likely poor current condition, and a moderate adaptive capacity.

Habitat changes and a loss of key flowering plants are the biggest threats to this species. Bilberry bumblebees have some scope for adapting to climate change, especially if habitat management focuses on improving floral diversity during nest-building season.

Current condition:

The UK bilberry bumblebee population has declined rapidly in the last few decades. Habitat loss and degradation is thought to be the main cause, as development and mismanagement have resulted in the loss of flowering plants they rely upon. It is likely that populations have also followed this pattern in the PDNP, but due to limited local data and a lack of historical data, this is difficult to assess.

Imported commercial bees bringing in new pathogens and parasites pose a threat to wild bee populations. The current risk level for bilberry bumblebees is unknown but potentially large.

Pesticides are known to impact bumblebees and increased usage has been recognised as one of the causes behind UK bee decline in the last 60 years. For bilberry bumblebees in the PDNP this effect may be reduced due to limited arable cropping and their status as a moorland edge specialists. The real effects of pesticides on PDNP bilberry bumblebee populations is unknown.

Wildfire has probably had a large impact on bilberry bumblebee populations. There were 552 wildfires within the PDNP boundary between 1976 and 2018. Habitat destruction by wildfires on both heather moorland and grassland is difficult to recover from especially when it destroys nests and large areas of foraging ground. Moorland edges are particularly vulnerable as that is where bilberry bumblebees tend to be more abundant.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

Queen bees are sensitive to food availability levels when they emerge after hibernation. Mild early springs could see early emergence of bees that have limited food sources. Late frosts could then compromise the bees further as severe cold snaps can cause their food plants to die. With depleted fat reserves, these queen bees are unlikely to survive if their food sources dry up. Loss of queen bumblebees has a detrimental effect that could cause population decline. Data Certainty: High Extreme events such as flooding and drought are likely to affect nests and foraging habitat. Changes to rainfall and temperature could also alter forage plant flowering periods, potentially creating a phenological mismatch between the flowering season and nest building. Data Certainty: Low This would mean that new queens might be unable to reach maximum size before hibernation. Fewer bilberries in flower during critical periods may mean that less nectar is available for worker bees, resulting in reduced nest success. On the other hand, better plant growth conditions caused by climate change may increase the productivity and flowering length of key plant species such as bilberry and legumes, giving the bilberry bumblebee an increase in food sources that could improve their condition and increase population sizes. Data Certainty: Low

A study of Finnish bumblebees found that queen size before hibernation can determine the sex allocation of colonies (queen/worker/male ratio) ultimately changing the population dynamics and survival rate for future generations. Data Certainty: Moderate

Climate models predict a reduction in suitable climatic conditions for bilberry bumblebees. As a cold adapted species, warmer temperatures are likely to be less suitable for bilberry bumblebees and drive their decline in the PDNP. One study predicts a loss of bees from the southern part of PDNP by 2050, and in a higher emissions scenario complete loss of bilberry bumblebees from all of the PDNP by 2100. Data Certainty: Moderate

Other indirect climate change impacts

Hotter, drier summers put moorland habitat at increased risk of wildfire. Stands of bilberry and heather within this moorland habitat mosaic along with legumes on the edges are likely to be lost if wildfire occurs. This loss of foraging ground along with damage to bumblebee nests may cause bumblebee populations to crash in some areas and decline in others. Data Certainty: Moderate

Invasive or other species interactions

Temperature increases are likely to lead to increased survival of pests and pathogens throughout the year. Pathogens and parasites in bilberry bumblebees may compromise their immune system leaving them vulnerable to other stressors such as habitat change. Loss of bumblebees that are overcome by these stressors will likely lead to population decline in affected areas. Data Certainty: Moderate

Nutrient changes or environmental contamination

Increased plant growth rate due to the increased availability of CO2 in the atmosphere, may lead to an increase in the use of herbicides in some areas such as waysides and verges. Herbicides may cause a decrease in the floral resource availability that bilberry bumblebees rely upon. Reduced food resources can impact bumblebee fitness and may also cause reduced breeding success. Data Certainty: Moderate Along with herbicide increases, pesticide usage may also increase as warmer temperatures support large numbers of some insects. These pesticides are likely to penetrate deeper into the dry soil seen in hot, dry summers and may then be taken up by wildflowers absorbing any liquid present. The bilberry bumblebees’ exposure to the pesticide may then be two-fold as they are exposed to the initial application as well as the contaminated wildflowers. This can then impair foraging ability and cause population decline. Data Certainty: Low

##Human behaviour change Land use choices and management regimes can greatly affect the viability of bilberry bumblebees to survive in any given area. Increased intensity of burning or grazing of moorland habitat is likely to damage large areas of bumblebee foraging habitat. Under-management on the other hand could result in the loss of key food plants as they are outcompeted by scrub or other plant species. A mosaic habitat with a mixture of scrub, woodland and foraging plants can be beneficial if the area is carefully managed to ensure bumblebee food resource and nesting requirements are met. Data Certainty: Low

What is the adaptive capacity of bilberry bumblebees?

Overall adaptive capacity rating

On the southern edge of their range in England, bilberry bumblebees are found on moorland throughout the Dark and South West Peak. They have some opportunity to move north due to reasonable connectivity with other moorlands in the South Pennines. In general, bumblebees are well buffered against fragmentation due to their exceptional foraging skills. They are able to forage across large distances, communicate successful foraging to other workers, and are flexible in their use of food sources. Data Certainty: Moderate

The bilberry bumblebee is a generalist forager that has a strong connection to bilberry and heather. Food availability in the form of bilberry and other key plants such as legumes are important for maintaining the population within the PDNP. Loss of these plants or changes to their flowering season could slow or prevent successful recovery, especially on either side of hibernation. Habitat loss or damage to nests could also interfere with recovery or cause population declines. Data Certainty: Moderate

Environmental land management schemes are available to help restore habitat and improve meadows for pollinators. In Yorkshire, a study on hay meadow restoration demonstrated an increase in bumblebee numbers within restored meadows. Importantly, bilberry bumblebees were seen foraging in these restored meadows which show the bees’ ability to adapt and expand their foraging area when habitat is positively managed near existing populations. The Countryside Stewardship Scheme has a Pollinator and Wildlife Package available to farmers which helps encourage positive habitat management such as enhancing food sources for pollinators. In addition, the National Pollinator Strategy sets out ways in which people and organisations can help pollinators, with a focus on expanding food, shelter and nest sites – the basic requirements for bee colonies. Data Certainty: High

Within the PDNP, the National Lottery Heritage Funded ‘Pollinating the Peak’ project has been underway since 2015. The Bumblebee Conservation Trust set up the project to increase awareness of pollinators and how to help them. Volunteers and citizen scientists also contribute their time to bumblebee surveys in the PDNP, which increases knowledge about the local population, identifying bilberry bumblebee locations and could aid management decisions in the future. However, the project funding is time-limited. Detailed ecology and population estimates are currently unknown. Data Certainty: Moderate

Key adaptation recommendations for bilberry bumblebees:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Continue and build on bumblebee surveys within the PDNP to improve knowledge of local populations.
• Improve habitat management: encourage establishment of bilberry and legumes; limit grazing/mowing during nest-building season; limit pesticide/herbicide use particularly during hot summers.
• Encourage further uptake of environmental land management schemes by farmers within the PDNP.

Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• Assess foraging habitat and identify areas that need improving such as those with a low diversity of food sources and areas where food is unavailable during nest-building season in spring.
• Develop fire contingency plans, and ensure management of habitats reduces fire risk e.g. rewetting and increasing species or structural diversity. Influence visitor and behaviour management plans and practices to minimise ignition risk.