Bumblebees who brave the winter

By Nicola Temple

This past weekend, my family and I met with friends in the village of Shipham, in Somerset, for a walk. It was torrential rain, yet we were determined. We dressed ourselves and three children under the age of 10 in waterproofs and set out. We arrived at a local country pub, not more than 3 km away, resembling drowned rats. And as a Canadian living here in the UK, I still marvel at the fact that nobody took one bit of notice at the state of us. It’s what you do. You get wet. You find a pub. You hunker down for a hot Sunday lunch. And you hope it tapers off before you have to head out again. (It didn’t.)

Pollinators, at least of the flying insect variety, aren’t terribly keen on this kind of weather either. Most hunker down for the winter months as there is generally not a lot of nectar to forage this time of year anyway. How they do this depends on the species. Honeybees reduce the colony to a minimal size and rely on their honey stores to see them through, while they dance in order to regulate the temperature of the hive. Most bumblebee colonies die out completely and the queens that mated at the end of the season find a place to hibernate. Solitary bees may hibernate as adults or as larvae, emerging only when the weather conditions are suitable. To each their own.

Martin Cooper spotted this buff-tailed bumblebee queen
foraging on his Mahonia flowers in Ipswich on a sunny
January day in 2015.
Photo credit: Martin Cooper [via Flickr CC]

However, there is one flying pollinator that can be spotted this time of year here in Bristol, and indeed, other warmer regions of the UK. It is the common buff-tailed bumblebee (Bombus terrestris). This species was first spotted during the winter of 1990, in Exeter. Sightings have been increasing ever since and include nest-founding queens, workers and males, suggesting this is a winter generation of the species.

The mated queen will emerge from her subterranean dormant state (diapause) during warm winter weather and set about establishing a new colony. The potential cost of waking up early is that the warm weather could be short-lived and temperatures could plummet. The benefit, of course, is that there’s nobody to compete with for food. If successful, the queen can establish a colony before the other pollinators even wake up from their winter nap.

Introduced plants provide winter forage

Of course, there is potentially another cost to emerging early – there could be nothing to eat. Bees are able to forage at temperatures around 0oC, but if there aren’t enough plants in flower, they won’t find the pollen and nectar needed to sustain the colony. Few native UK species flower in winter, but species introduced by avid gardeners to bring some winter colour to the garden, also bring some much-needed food to the buff-tailed bumblebee.

Researchers at Queen Mary University of London and The London Natural History Society, conducted a study of buff-tailed bumblebees foraging in London parks and gardens during winter about ten years ago. They wanted to see just how much food the bees were finding as food is directly related to the success of the colony.

The researchers found that there was plenty of forage to sustain the colonies and, in fact, the foraging rates they recorded near the end of winter were equivalent to peak foraging rates found in the height of summer. This doesn’t mean that the winter-flowering plants, such as the evergreen shrubs of the Mahonia spp., are providing more pollen and nectar than all the plants in the height of summer. But it does mean that each flower might have more pollen and nectar available because there aren’t other pollinators out and about also using the resource. The bumblebees, therefore, don’t need to go as far to find an equivalent amount of food and so they can collect it at a faster rate.  

Strategies for tolerating cold

Buff-tailed bumblebees aren’t as tolerant to cold as some other bee species; workers will freeze solid at about -7.1oC while queens freeze at -7.4oC. The bumblebees can obviously find warmth in the colony, but they need to forage and therefore be able to tolerate short spells of cold during the winter months. They may even need to tolerate cold temperatures for up to 24 hours as bumblebees often overnight away from the colony when they are unable to return from foraging.

Researchers from the University of Birmingham looked at the different cold tolerances of this bumblebee species a few years ago. They found that 50% of workers died after being exposed to 0oC for 7.2 days while queens could last over 25 days at this temperature – likely due to their fat reserves. However, as the forage study showed, the bees seem capable of finding food sources closer to the colony during winter months, which may reduce the likelihood of them having to endure cold temperatures for a lethal period of time.

These bumblebees may also have adopted some strategies to help reduce their possibilities of freezing. Pollen is an ice-nucleating agent in that it promotes the development of ice at higher temperatures. Other insects have been observed to expel any ice-nucleating agents from their gut when they experience low temperatures to avoid freezing. While this wasn’t observed in the bumblebees, it is a strategy that individuals might employ when caught out in the cold.

The more frequent observation of buff-tailed bumblebees in winter is thought to be a result of warmer autumn temperatures brought about by climate change. In a study from 1969, researchers reported a 6-9 month dormancy of all bumblebees in southern UK, so in a relatively short period of time there has been a considerable change in their seasonal pattern. There seems to be some flexibility in these patterns among bumblebees and for now, establishing winter colonies seems to be working for the buff-tails. However, with so many of our pollinators under threat, there is obviously also concern among the scientific community that more frequent extreme weather events could also spell disaster for these colonies that have selected to brave the winter months. As gardeners, we can perhaps do our bit by planting some winter forage species.

This year, the University of Bristol Botanic Garden will embrace a pollinator theme, with the aim of highlighting some of the lesser-known pollinators that are so important here in the UK. We love our pollinators, but research is still revealing so much about their unique and complex relationships with plants. So watch this space as we share some of these wonderful stories through our blog. We will also be posting pictures of pollinators we see in the Botanic Garden on our Twitter feed and Facebook page. But to see these polli
nators in action, take some time to visit the Botanic Garden. Make space in your busy schedule to watch nature at its best – it’s worth it.

Sources:

Alford DV (1969) A study of the hibernation of bumblebees (Hymenoptera: Bombidae) in Southern England. Journal of 
     Animal Ecology 38: 149-170.
Owen EL, Bale JS, Hayward SAL (2013) Can winter-active bumblebees survive the cold? Assessing the cold tolerance of 
     Bombus terrestris audax and the effects of pollen feeding. PLoS ONE 8(11): e80061.          
     doi:10.1371/journal.pone.0080061
Stelzer RJ, Chitka L, Carlton M, Ings TC (2010) Winter active bumblebees (Bombus terrestris) achieve high foraging 
     rates in urban Britain. PLoS ONE 5(3): e9559. doi: 10.1371/journal.pone.0009559 

‘Tis the season…or is it?

By Helen Roberts

As I sit at my desk this morning, staring out the window, the weather is dire. There is slanting torrential rain and high winds, a typical December day perhaps.
Here in the UK, the seasons are changing and we are experiencing extremes of weather. For example, we have had wetter, milder winters in the southwest over the last couple of years along with increased flooding, particularly on the Somerset Levels. And then there was the very slow start to spring this year, with temperatures well below average in April. This was followed by a very hot end to the summer and warmer-than-average temperatures throughout autumn.
These changes to the seasons are linked to global climate change and are throwing the UK’s wildlife into disorder and affecting the fine balance of habitats and ecosystems. This is not a good scenario for biodiversity in the UK. Seasonal timing is off. When seasons start and end is shifting, and the length of the season itself is changing, making ‘growing seasons’ a more fluid concept. There is also increased risk for most gardeners of a ‘false spring’. Many plants and animals are changing their geographical ranges in order to adapt to these changes.
One of the most significant effects has been the disruption of lifecycle events and these are manifesting themselves in different ways. Bird migration, insect emergence, incidence of pests and diseases and flowering times are being thrown out of kilter.  
Researchers from the University of East Anglia recently analysed 37 years worth of data from the UK Butterfly MonitoringScheme (UKBMS) and found that extreme weather events were causing population crashes of butterflies. Uncommonly high rainfall events during the cocoon life stage affected 25% of UK butterfly species. And more than half of species were affected by extreme-heat during the overwintering life stage, possibly due to the increased incidence of disease or the effect of a ‘false spring’, causing butterflies to emerge too early only to be decimated by a return to cooler temperatures.
Warm temperatures are not all bad for butterflies though, as they will benefit from hot temperatures over the summer months when they are in their adult form and resources are plentiful. However, if populations crash more frequently than they expand, these extreme weather events could threaten UK butterflies.
The spider orchid (Ophrys sphegodes).
Photo: Jacinta Iluch Valero via Flickr [Creative Commons]

Changes in seasonal timing are also knocking the relationships between plants and animals out of sync, including the delicate balance between plants and pollinators. Thiscan be detrimental to the balance of entire ecosystems. An elegant study carried out by scientists from Kew and the University of East Anglia found that earlier springs brought about by rising temperatures are affecting the relationship between a rare spider orchid (Ophrys sphegodesand its sole pollinator, the solitary miner bee (Andrena nigroaenea).   

This particular orchid has a flower that resembles and smells like a female miner bee and it uses this deceit in order to lure the male miner bee in. The male attempts to mate with the flower and by doing so, pollinates the flower. The plant has evolved to flower at the same time as the male bees emerge, but before the females do.
What the researchers discovered, by looking at the data set going back to 1848, was that rising temperatures are causing the relationship between orchid and bee to break down. Although rising temperatures cause both the bee to emerge and the orchid to flower earlier, the effect on the bees is much more pronounced. The male bees emerge much earlier and the orchids now flower as the female bees emerge. This means the males are not “pseudocopulating” with the flower because the real thing is already available and so the rare spider orchid is having fewer pollinations.
However bleak this picture may seem, plants and animals do have the ability to adjust to seasonal changes caused by climate change, it is just whether they can adapt quickly enough for these intricate ecological relationships to remain intact.
Helen Roberts is a trained landscape architect with a background in plant sciences. She is a probationary member of the Garden Media Guild and a regular contributor to the University of Bristol Botanic Garden blog.


References

Bristol is buzzing, how the city is helping pollinators

By Helen Roberts

There has been a substantial amount of press coverage recently on the plight of our pollinators. They are now less abundant and widespread than they were in the 1950s. A number of threats are responsible, including habitat loss, disease, extreme weather, climate change and pesticide use.
A swathe of flowers for pollinators bring a
lot of cheeriness on a grey autumn day on
Horfield Common, Bristol.
Photo credit: Nicola Temple
There is not one smoking gun among these threats, but rather the combination that has endangered some species in the UK. Loss of wild flower rich habitat (due to intensive agriculture, industrialisation and urbanisation) escalates the effect of disease, extreme weather, climate change and pesticide use. Without food or shelter, pollinators are more vulnerable.

 Whilst visiting the University of Bristol Botanic Garden this autumn, I noticed the abundance of pollinators busily visiting many different flowers from the orchid look-a-like flower of Impatiens tinctoria to the swathes of Rudbeckia sp. and Verbena bonariensis. This year saw the 6th year of the University of Bristol Botanic Garden hosting the Bee and Pollination Festival in September. The Community Ecology Group from Bristol’s School of Biological Sciences was exhibiting and promoting their research as well as the exciting Get Bristol Buzzing initiative.
To find out more about pollinator research at the University, I met up with Dr Katherine Baldock, a Natural Environment Research Council Knowledge Exchange Fellow from the School of Biological Sciences and the Cabot Institute, to discuss the group’s work.
“Most people know that pollinators are important, but quite often don’t know what to do to help them, “ explained Katherine. “And this is where our research at the University comes into play”.
The aim of Katherine’s fellowship is to improve the value of the UK’s urban areas for pollinators by working with various stakeholders, such as city councils, conservation practitioners and the landscape industry. 

Translating science into solutions

NERC KE Fellow Dr Katherine Baldock.
Photo credit: Nicola Temple.

Up until 2014, Katherine worked on the Urban PollinatorsProject, which is researching insect pollinators and the plants they forage on in urban habitats.
Building upon research from this project and her current Fellowship, Katherine and her Bristol colleagues have contributed to the development of  a Greater Bristol Pollinator Strategy(2015-2020). The University research group has teamed up with Bristol CityCouncil, the Avon Wildlife Trust, Friends of the Earth Bristol, Buglife, SouthGloucestershire Council and the University of the West of England to implement this with the aim of protecting existing habitat and increasing pollinator habitat in the Greater Bristol area.
The group is also raising awareness of the importance of pollinators to a wide-ranging audience within the city and further afield. This is the first local pollinator strategy within the UK and follows closely in the wake of the Department for Environment, Food and Rural Affairs’ National Pollinator Strategy launched in 2014. It will help to promote aspects of the national strategy relevant to urban areas and hopefully set a precedent for the development of other local pollinator strategies throughout the UK.
The local pollinator strategy outlines actions that will help fulfill the strategy aims, including:
·         formation of a Local Pollinator Forum intended to share knowledge and best practice,
·         establishment of a joined-up approach to pollinator conservation by linking projects through the Get Bristol Buzzing initiative,

·         working with the public in local areas to explain actions they can take as individuals.

“Urban green spaces are important corridors for wildlife and help to provide linkages across the country”, explained Katherine. I envisaged a series of insect aerial motorways linking the whole of the UK, invisible threads connecting countryside, urban fringe and city centres.

The bee link-up

The Get Bristol Buzzing initiative is doing just that, as one of its strategic aims with the local pollinator strategy for 2016-2020, is to “Map pollinator habitat and identify target sites that allow habitat networks and stepping stones to be created to enable pollinators to move through urban areas”.
Katherine talked about how engaging the public at ground level was really important to Get Bristol Buzzing. The initiative is the pollinator component of My Wild City, a project whose vision is for people in Bristol to help transform spaces into a city-wide nature reserve. A number of interactive maps have been created that allow people to add what they have been doing in their area to help wildlife. The Get Buzzing initiative will feed into these maps.
Kath said, “The fact that you can add yourselves onto a map makes the Get Buzzing Initiative really visually appealing to people and much more personal.”

So, what can you do at home to help urban pollinators?

·         Plant for pollinators. Think about what plants you have in your garden. Could you change the planting or improve on it to make it more attractive to pollinators? Think about growing species that have nectar and pollen rich flowers and let your lawn grow longer to allow plants to flower.
·         Avoid pesticides. Most gardeners like their plants to remain pest free but avoid the temptation to use pesticides and accept the fact that you will lose some plants to pests. Instead try to encourage wildlife that will devour those pests or cultivate plants that will deter pests. 
·         Provide habitat. As pollinators need a home, you can always make your own nest boxes if you want to give your pollinating visitors a helping hand by drilling holes in a log or by bundling up lengths of hollow sticks such as bamboo. Visit the Botanic Garden’s bee hotel for inspiration!
“Setting aside a wild bit of garden can help pollinators by providing food, but provides nesting sites too”, remarked Katherine.

Additional information:

·         The Urban Pollinators Project was recently listed as one of the top 10 ground-breaking research projects in the Daily Telegraph. Read more.

·         Results from this research have recently been published in the Proceedings of the Royal Society B with more publications in press. A list of publications can be found here.

·         You can read more about Dr Katherine Baldock and the Urban Pollinators Project on page 7 of the 2015 edition of the Cabot Institute’s magazine.

Green roofs part II: lofty havens for wildlife

By Helen Roberts

The green roof industry has been aided over the past few years by an unlikely character. The black redstart (Phoenicurus ochruros), a robin-sized bird of strange habits, has not only helped draw attention to the green roof industry, it has advanced development of green roof design.
The black redstart is unusual in its call, looks and ecological preferences. Its song starts with a hurried warble followed by a sound similar to that of scrunching of a bag of marbles. Males have a fiery red tail and the species has a propensity to hang out in industrial places.
Within the urban environment, brownfield sites can be rich in biodiversity and can be lost when they are developed. The story of the black redstart is inextricably linked to that of humans and urban centres. Black redstart population numbers have fluctuated in the urban environment due to human activity, and this is where the story of the black redstart has impacted the green roof industry in a positive way.
During and after the Second World War the black redstart population soared because bombsites provided a habitat that closely replicated their preferred habitat found on the scree slopes of the Alps. With redevelopment of areas of London, however, populations declined. Other cities also saw a drop in numbers as a result of development.

Laban Dance Centre in London.
Credit: rucativava,
CC-BY-SA-2.0, via Wikimedia Commons

Deptford Creek in London, an area that was earmarked for development, was important for its populations of black redstarts. The developers were pushed by wildlife groups to provide suitable habitat for the birds through the implementation of green roofs. This truly innovative solution to mitigate the decline in black restart populations led to the development of green roofs designed specifically for black redstarts. The rubbleroof of the Laban Dance Centre in London, installed in 2000, was the first of these in the UK. Rubble roofs, such as the Laban Dance Centre’s, replicate the features of a brownfield site and often incorporate materials from the original site. They have a mix of aggregate materials such as crushed brick and concrete, stones and boulders. The Laban Dance Centre roof also incorporates features such as logs and sand boxes in order to study nesting bees. It has been monitored since 2002 and a number of rare invertebrates have been recordedusing the habitat.
Numerous studies have shown that green roofs help support several Red Data book invertebrates and UK Biodiversity Action Plan species such as the brown-banded carder bee (Bombus humilis) and the nationally scarce Bombardier beetle (Brachinus crepitans) and that these green roof conditions can be replicated at other sites.

The right plants for the right roof

Incorporating the right plant species in to the design of a green roof is important for achieving biodiversity objectives. Simple sedum matting has been shown to have little ecological benefit for invertebrates, though they do provide sources of food for foraging bees in summer.
A truly exemplar green roof that is rich in plant species is the Moos Filtration Plant in Zurich, which cleans all the water for the inhabitants of Zurich. Yet, this green roof came about by chance as there was no original intention to create a green roof as part of the building design. When the filtration plant was built, the multiple roofs were covered in exposed waterproofing which subsequently caused the water below the roof deck to become polluted with bacteria due to high temperatures during the first summer. In order to moderate the temperature of
the roofs, a 5cm sand and gravel layer was laid down followed by a layer 15-20cm deep of local meadow topsoil. This soil was teeming with flower and grass seed and it became a flourishing 30,000m2 meadow. Today these expansive roofs provide habitat for 175 species of plants, many of which are rare and endangered at a local and national level, including 14 species of orchid. The roofs now have special protection under Swiss nature conservation laws.
 

Due to the pressures of habitat loss through urbanisation, it is becoming increasingly important for biodiversity to be retained. If land is lost at the ground level through building, then green roofs help provide stepping stones above for wildlife and can provide valuable habitat for flora and fauna that would not ever be found on a conventional roof.