Bumblebees, cavities, nest material and conflict with birds
In temperate forests, birds and bees nest in natural tree cavities. Bumblebees are small insects that, unlike birds or mammals, are not physically strong enough or have the physical capabilities to excavate tunnels, cavities or carry nest material, although some species may be able to utilise material right next to the chosen nest site such a B. pascuorum. Therefore it would be advantageous to them if they could find a nest site that offered protection from the elements, was dry, concealed and had inside it a quantity of plant material as bedding. A cavity, hole in a tree, natural tree cavity, mammal nest or bird nest box, as found in many UK gardens, with bedding material, would to say the least, be very desirable for a nest seeking queen. It is well documented that bumblebees occupy various abandoned mammal nests.
Ground nesters or tree nesters
Many UK bumblebee queens nest in, on or near the ground surface, where mammalian nests would far outnumber natural tree cavities. Competition for such sites, between cavity nesting birds, e.g. great tit (Parus major) or blue tit (Cyanistes caeruleus) with some species of bumblebees, such as the aptly named, tree bumblebee, Bombus hypnorum, could easily occur. Parks and gardens where natural tree cavities may be scarce, would be ideal places for birds or bumblebee bees to nest. It is known that B.hypnorums do occupy abandoned birds nests in tree holes.
Bumblebees display visual warnings to deter predators, i.e. their colouration. They also back this up with a warning signal, their buzz, often heard by bumblebees when they defend their nest site or are attacked. If you still don’t get the point (!) then they have their sting. Predators soon learn either a prey item is distasteful, poisonous or harmful to themselves and once you have been stung by something, you would remember what it looked like, especially if you were about to eat it! Some birds have learnt how to deal with bumblebees stings and eat their insides out. One such UK bird is the great tit and under certain circumstance the blue tit may well eat them as well, although predation by these birds is not very common.
My wildlife garden
This year, 2013 was a rather odd year for me and bumblebee nests. Having moved house only a few years ago, in 2009 the garden needed a lot of work doing to attract wildlife. I have placed all of my bird boxes, bumblebee nest box along the mostly ivy clad back fence with the bird feeder near the study window, so at once glance I can see them all. Over the past few years I have had a either a great tit or blue tit nest box hanging in a tree each year. I exchange the tit boxes, one year blue tit the other great tit nest box in the same tree. Each year the appropriate sized hole has attracted the appropriate tit. Both species nesting in the same garden in their respective nests. I also had 2 wren nest boxes in the garden and another more generalist nest box hanging from the brick wall of my garage, overlooking the garden. All of the used nest boxes are throughly cleaned every autumn and contents removed, then replaced for the winter months for use by winter roosting birds.
Supply of nesting material
As is usual in spring, I place outside, a ground bird table on top of a disused concrete bird bath. On the ground table I place moss from the lawn, bits of dried grass, kapok and other soft materials which is used by great tits, blue tits, robins and blackbirds every year. It is rather satisfying to see it especially in the blue and great tit nest boxes, their nests being easy to find! It is usual for them to start off gradually and as the weather warms up, the nest gathering activity increases.
Busy birds making nests
Although rather late this year, both the great tit box in the tree and the blue tit nest box on the garden fence had birds making nests in them, using the material from the ground table feeder, which is easily viewed from my study, so I can see them. I regularly top it up, as required. I check them to see how the nest is taking shape. When building their nests they deposit the nest material where it is needed and then leave. They rarely stay in the nest box when building the nest. As usual this year, I saw both species going in and out with material over several days, then poor weather would terminate this practice. Warmer weather would resume the activity. After a few days of warmer weather late in the spring, I noticed the birds were not entering the nests boxes. In fact there was not as much blue tit activity as was usual. There are always ‘battles’ between the great tits and blue tits, busy chasing each other from their respective nest boxes or domineering the feeder, especially by the great tits who appear to simply want to chase the blue tits away, visit the feeder in order to do so and then not even feed! I did not suspect they were incubating either as when they incubate the male usually enters with food for his mate.
Nest material gathering great tits
This particular morning, early as I always rise early, I saw the great tits carry fresh material from the ground feeding table to the nest box on the garage wall. I thought this strange and would look at the nest later to see what was going on as I had watched them over the last couple of days doing the same.
Nest material gathering by blue tits
Later that morning I caught a glimpse of a female blue tit carry away some nesting material. I expected to watch it go into the blue tit nest box, which is only 3 feet away as I had watched over the past few days, but not over the past 2-3 days. But it did nt. It flew off in the direction of a small copse. I though this was unusual and a rather risky action for this bird to undertake. Right above its head was a blue tit nest which had a pair of resident blue tits in it having adopted it. To enter so close to this nest box was risky. She could easily have been attacked by the resident pair. Obviously I felt she would be aware of the risk and decided to take it. She obviously knew where the bedding material was. I suspected she had observed it some time ago when perhaps visiting the garden feeders earlier in the year. I have two male of robins often fighting sometimes viciously in my garden as I think my garden fence forms the boundary between two territories. So another bird from another pair not nesting in my garden is not unusual. I thought it was simply another female from another pair gathering material for a nearby nest, who had chanced her arm!
Great tit nest box, nest abandoned.
I have never had in any of my gardens two pair of great tits nesting. The gardens are simply too small. I found it strange as I watched, through one of my casual glances in the study, the great tits were building another nest inside the bird box on the garage wall, (which failed) about 12 feet away and in full view of the nest box that they had been building their nest in. Birds were carrying material in from early morning over a couple of days or so, much more intensely than usual as usually they start off and gradually gather material and as warmer weather starts this activity increases. The afternoon of the morning I saw the blue tit gathering nest materials as described above I checked out the great tit nest box, by removing the front cover of the Schwegler box. I wanted to see what was happening inside the now abandoned nest box. Obviously there was a reason for this. I assumed it was the same great tits, I had observed earlier over the past, taking nest materials and making their nest in the great tit box, although I cannot state that as fact! Upon opening the front of the nest, I found a complete bird nest inside. Why had they simply wasted time and energy on a nest then suddenly abandon it, to start afresh a few feet away? I left the nest inside the box. Nest morning they were still gathering material for the new nest.
Blue tit nest box, nest abandoned
I open the front of the nest box, looked inside and found a fully formed nest with one very cold egg inside it. I replaced the front and left it in situ. It too had been abandoned. Why? Cats and grey squirrels are regular visitors and I thought perhaps they had ‘spooked’ the birds, causing them to abandon them. I have had nest boxes for over 35 + years and am aware that they may lay one egg a day leave the nest and come back later, usually in the morning to lay another egg. They time their egg laying to the weather and their incubation to the flush of oak leaves. Occasionally I have found a single egg in a blue tit nest and it has been either abandoned perhaps one partner has been killed by one means or another or abandoned because a lack of food or some other reason. This year has been odd. I then remembered the blue tit earlier that morning. Was this the same female that had built her nest in this nest box and she was now frantically building another nest nearby using the nest material that she knew was there? Why both nests apparently abandoned at the same time? Both species have nested in the same garden simultaneously every year with cats and squirrels present.
Again at this time the wren boxes were not being used, although they were rather low down, in case bumblebees were attracted to them.
‘Baited’ nest boxes
I left both bird boxes with their nests in situ with contents inside, pondering what to do with them and why the birds had deserted. Early the next morning, I opened blue tit nest box, it was still cold and no new egg had been laid. I moved it complete with nest and egg to an adjoining wooden fence which was completely clear of any vegetation growing on it and easily viewed from the fence it had just been removed from to fence just a few yards away. The new site was a site I had placed it and where a few years ago B. lapidarius had nested in it. To see if I could attract bumblebees to both nest boxes I placed my bumblebee ‘baited’ bedding material that I now use for all my bumblebee nest boxes. I simply placed it on top of the nests and egg. The great tit box and nest in were left were they had been placed originally. I also added bumblebee ‘baited’ bedding material to one of the Schwegler wren nest boxes, moving it a little higher up the fence to see if I could attract bumblebees. B. pratorum had used it in the past so I put it in the same location.
Great tit nest box, new occupant
Later that morning I had a quick glance from my desk and watched intently as I saw a B. hypnorum queen going into the great tit nest box (which had not been moved) with pollen on her legs. She knew exactly where the nest entrance was, no inspection before hand, no orientation flight, just flew straight in. This to me implies that she had started to nest already and was gathering pollen to stock pile for her newly established nest. I cannot think of any other plausible explanation. I was simply lucky to look up at the right time. She may have been out foraging, when I removed the nest front as there was no warning buzz when I tapped the nest box. I did not disturb the bird nesting material, just added to it.Knowing this I made more frequent observations of this new activity in that nest box. She made several trip that day and over a few days. A few days laters I waited for the queen in the great tit nest box to leave and found a queen B. hypnorum dead inside. This nest is now very busy with workers.
Blue tit nest box, new occupant
Then within a day or two of moving the box, just a few feet from its original site, with nothing else along the wooden fence to obscure it, I saw a B. hypnorum queen enter the ‘baited’ blue tit nest box. She also went straight in and knew where the entrance hole was. I watched confident that she was busy establishing her nest due to her regular pollen laden trips over the next few days. But nearing the end of May, I saw nor heard any activity from this nest box by the queen.
I removed the front to see a small hole in the bedding material. Two days of observing no nest box queen activity or buzzing upon tapping, I removed the front and found the nest had been abandoned, complete with an empty honey pot and sealed cells, containing bee larvae. Likely she had died for some reason or other.
Upon opening the cells I found bumblebee larvae.
Wren nest box, new occupant
A short time later, I decided to check out the Schwegler wren box I had also ‘baited’ with bumblebee having not seen any activity there, particularly as the weather was not so good. and I was rather busy with other things. After receiving no response from the ‘precautionary tap’ on the nest box, I lifted the nest box from its hook, lay it on the ground, opened the top lid and gently moved the bedding. Then and only then did I hear the buzz and an angry B. hypnorum queen started to emerge from underneath the bedding! This may well have been because she was at a certain stage in her own nesting process and decided to remain silent. The top was quickly re positioned and secured and left on the lawn for her to settle down, to be positioned in the same place a short time later. This nest is now thriving, producing numerous workers. I have had B. pratorum use this particular nest box in the past.
Beside the above queens, I attracted 3 other queens into ground nest boxes, with only one surviving. Details to follow.
Bombus hypnorum new to UK
B. hypnorum was first reported in the summer of 2001, near the village of Landford, on the northern fringes of the New Forest. As the specimen was brightly coloured, with little or no obvious hair loss and little damage to its wings, researchers concluded that there was little evidence that it had flown across the Channel. In other words it was simply too healthy looking to have made such an arduous and dangerous journey. That being the case it was presumed that it was a resident bumblebee. At that time researchers could not decide whether the bee came from an established colony or through being imported deliberately from Europe and used in a greenhouse. At that time researchers concluded that this was one of the species of bumblebee that was capable and most likely to become established in the UK. They were right! It had previously been described as showing ‘a stronger preference for areas inhabited by man than the remaining Scandinavian Bombus spp’. Right again! Another researcher considered that it had become more abundant in Belgium and Germany during the twentieth century, possibly as a result of increasing urbanisation. Goulson’s studies found that in England, gardens were shown to be a stronghold for other bumblebee species, e.g. B. terrestris. How right they all were! They also conclude however that there was no reason to believe that it will do any harm, for example by competing with native British species, since it was already an established European species. This may be true for bumblebee species, however it may now not be true for other species of wildlife, such as blue and great tits. Something that then would simply have not been considered.
Its range from the Kola Peninsular in Arctic Russia and continental Europe, from Landford UK to my garden in a relatively short time. A massive UK expansion range. It is strongly associated with parks and gardens. I do not know how it actually arrived here, possibly by flying over the channel in numbers? Now they are in Iceland. A queen was first sighted August 2008 and by 2010 was far more widespread and in 2013 is still increasing its range there. Can they fly such a distance, where they introduced or did they possibly come by air transport or ship. They do not know.
Why abandon nests and egg?
I felt something had spooked the birds and it was not the cats or squirrels. I strongly suspected that the B. hypnorum queens had something to do with the birds abandoning their nests. They have never abandoned them in the past nor has any B. hypnorum nested in exactly the same boxes before that had been in use by birds. If you think about it, being inside a dark nest box, with a loud buzzing sound, which birds may have encountered for themselves in the wild and then having the nesting material vibrating underneath you may well be scary to a nesting bird! Besides, do our resident UK birds recognise it as a bumblebee, if so which bumblebee. Would B. hypnorum have a different tone or pitch that the birds did not instantly recognise? Being an obvious bumblebee buzz sound that was not recognisable, how big was it, would it attack and sting? Should they be more wary of it?
Bumblebee queens eject birds from nests
Researchers recently studied how some species of bumblebees buzzed inside bird occupied nest boxes in order to steal a birds nest, describing it as a form of kleptoparasitism. It is known that some prey items use warning signals which predators recognise and steer away from prey that by experience they have found to be distasteful or poisonous thereby avoiding them, (aposematic warnings). Indeed bumblebees use their visual colourings and auditory buzz noise to deter attack on themselves and their nest. Here inside a dark nest box, visual warning are not visible. Was the buzz from a prey item or a food item? Great tits are known predators of bumblebees and under certain circumstances, blue tits may also predate upon bumblebees. In my scenario, we may well have potential predators of bumblebees, scared from their nests by their bumblebee prey.
Dead bumblebee on toothpick
In their experiments, researchers used a dead bumblebee, affixed onto a toothpick,q itself affixed to a small modified speaker. They completely buried the speaker in the nest material and left the bumblebee partially visible and inserted a camera to watch the bird reactions as they emitted the warning buzz from the speaker inside the nest. Cameras were also installed and hand reared tits were used. Basically the hand reared birds paid no attention to the bumblebee or its buzz. They concluded that the reared birds had never come across bumblebees and their defensive strategies so were unaware of any danger. To be stung you would remember what stung you!
They later studied the results in the field using wild subjects, with the dead bumblebee device and monitored birds inside nest boxes that had attracted wild queen bumblebees. The results were very different. Here the nesting wild birds, with wild bumblebee queens/bee device inside became distressed upon hearing the buzz and often flew out of the nest, many abandoned it. For a control they used common bird songs and the incubating birds were less stressed and did not abandon the nest.
Recorded sounds of bumblebees buzzing were played to the birds when they were incubating or feeding their young. They found that after placing the dead bee inside a nesting great tits nest, and playing the bumblebee warning buzz, the birds were prevented from continuing with their nesting activities and abandoned the nest, as did the birds with live wild bumblebees in the nest box. This demonstrated that the aposematic signals may not only be beneficial just to deter predators but also beneficial in securing a much prized resource, i.e. the nest box and bedding material.
Other ousting by bumblebees on birds
In Turkey, Rasmont el al, found that a bumblebee, Bombus niveatus vorticosus, ousted common restarts, (Phoenicurus phoenicurus) by invading their nests, then by continually rearranging the bedding, sometimes covering the bird eggs or even the chicks, to the obvious annoyance of the birds. The birds seemed to be considerably disturbed by the activity and the bees presence. So much so that they deserted the nests, eggs or chicks without putting up any fight at all.
B. hypnorum strategy
This strategy to steal a birds nest, a form of kleptoparasitism, is rather risky for the bumblebee and takes some planning. It reminds me of a cuckoo bumblebee, if she enters a nest when there are too few or too many workers in the nest, she runs the risk of being overpowered by the workers or there not being enough workers to tend her own offspring after she was killed the resident queen. When a B.hypnorum queen enters a bird nest box and a bird is present, the likelihood of being spotted coming through the entrance hole could end up with her being killed, then presumably eaten. She would have to wait until the birds were not present. She would also have to time it so there was enough bedding material for her to make use of herself, to make the risk worthwhile. Plus the fact that the more bedding inside the nest, would offer her more protection from being detected. I would imagine she takes a quick sneak view of the nest and if the bird is present, she remembers the site and flies away to return and revisit. When there is enough material for her use and if the birds are not present she enters the nest box and buries herself underneath the bedding material. Upon arrival of the female bird who enters the nest to either incubate or start egg laying, the bird is spooked by the possibly unrecognisable sound of an otherwise familiar warning sound of a bumblebee. Each time a bird returns to the nest, she is met by this buzzing and vibrating of the nest material from underneath her body. The B. hypnorum keeps concealed and remains still and silent, until she is confident that the bird has not returned, by not hearing the bird in the nest and not having the nest material moved, adjusted etc., by the soon to be evicted nest builder. Then and only then can she start the establishment of her own nest. This may have been the case with the now successful, wren nest box nest, when I removed the lid and moved the bedding inside it.
In my case, which appears to support the research undertaken by Jablonski, did the bees scare the birds away? It certainly is possible having found the Jablonski work, something I had never heard of before. Neither have many others. I suspect it was highly likely in the great tit case. No electric buzzers needed! It could also have been possible in the blue tit case. Seeing a pair of blue tits regularly, several times a day at my feeder chipping away at sunflower hearts then carrying them in the direction of the copse I saw the female fly when she carried the nesting material makes me more likely to believe their nest was abandoned. These bees did ensure that for the first time since moving here, no blue tits or great tits had successful nests in my garden. The B. hypnorums may well have succeeded over their predators. The great tit nest failed, (above). Unfortunately I cannot say whether the great tits died in the new nest because of a late spring, moving nest sites or whether or not another B. hypnorum moved into the nest box, as I cannot identify what the dead insects or cocoons are. It certainly is possible.
This new species of bumblebee must be looked upon my profession researchers as a huge opportunity to undertake some new areas of research facilitated by this bumblebees arrival here. Areas of research they could not undertake because it is so new. As this bumblebee occupies a fairly unique niche and is new to the UK as regards UK bumblebees, a key factor to study here would be, not only its affect on other bumblebees or the crops it may pollinate, but its potential affect on other wildlife, in particular cavity nesting birds, in urban areas as this bee favours such areas. It definitely affected birds in my garden. Does it share the same pests as our native bees, or does it aggressively defend its nest against all pests or predators. How are pests dealt with by these bumblebees on the continent? Will they ever become a problem for wildlife or humans? The strategy as described above, offers many different and novel ways to test new theories……. I have a video of males performing, for want of a better term, as ‘swarming dance’ outside each of the two active B. hypnorum nest boxes, opening up another area of research!!!……if only I was younger!!
“All my articles and videos, available free, are funded by my teaching and sales of award winning bumblebee nest boxes, solitary bee boxes, and wormeries. Please help by spreading the word and forwarding this link to your friends and colleagues. http://nurturing-nature.co.uk Thank you” George Pilkington
Feed back re this article
This article has been particularly noticed with considerable and interesting feedback obtained. Of particular note is the debate caused by differing perspectives on the observations I made about the behaviour of bumblebees. One perspective was that my observations were not valid scientific research that used a scientific methodology that would be used in scientific field trials or laboratory work undertaken by research agencies or universities. I would, in the first instance, have to agree with this perspective. However the purpose of my article was to communicate the observations I made which in the future I hope would be followed up by an extended scientific investigation by myself or others.
The article was written based upon my own natural history observations in my own garden. The observations in fact came about by accident at a particular moment in time. Of course there was no hypothesis to prove or disprove. No theory to prove or disprove or a methodology to follow. The article was not intended to withstand the scrutiny and rigours of a set scientific method. The article was simply me, an ‘amateur’ nature watcher, writing an account of an incident that happened in my own garden, over a few days observations, with a little investigation and research as to what happened and a possible answer as to why it may have happened., a piece of natural history writngs. Something that has been done by ‘amateur’s for hundreds of years. Just my curiosity as why, two birds nest both with fresh bedding material, (not old bird nest material), which to me appeared to be abandoned, one definitely (great tit) and one probably (blue tit).Why both nest boxes were used immediately by one species of bumblebee, with a queen being killed in one in one and another using a bird nest free bird box,(Schwegler wren box) making 4 queens of one species all using bird boxes.
The next step is, for myself or others, to further my initial observations and hopefully at some time in the future be subjected to rigorous scientific scrutiny using a valid scientific methodology. I would be particularly pleased if my observations are progressed in the future. I welcome the debate stimulated by this article and look forward to further points of view in the future.
Refs. Besides my own photographs, observations and experiences:
Benton, T (2006) “Bumblebees’ Harper Collins Publisher, London
Goulson, D. ( 2010). “Bumblebees behaviour, ecology and conservation” Oxford University Press, Oxford.
Goulson, D and Williams, P, (2001), ” Bombus Hypnorum, A new British Bumblebee” Br. J.Ent. Nat.Hist.
Down load it here
Jablonski, P G et al (2013), “Waring signals confer advantage to prey in competition with predators:bumblebeessteal nests from insectivorous birds”. Behavioral Ecology and Sociobiology.
Download it here…. DOI 10.1007/s00265-013-1553-2
Rasmont, P, et al, (2008), ” Ousting of the Common redstart (Aves: Turdidae: Phoenicurus phoenicurus) from its nests by the bumblebee Bombus niveatus vorticosus”, Ann.soc.entomol. Fr.(n.s) 44 (2) : 251-255
Olafsson , E. (2010 updated May 2013) Rauðhumla – Bombus hypnorum (Linnaeus, 1758) (Google translated) http://www.ni.is/poddur/gardur/poddur/nr/1244
With thanks to Stuart Roberts, BWARS, for the redstart information.
For more information and to help save bumblebees join the Bumblebee Conservation Trust.
You can download a detailed B. hypnorum information sheet here from the Bumblebee Conservation Trust written by Clive Hill
For those of you interested in garden birds,the BTO Garden Bird Watch scheme may be of interest