BCT Artificial Light and Wildlife Symposium 2014

The Artificial Lighting and Wildlife conference was held in London on the 20th and 21st of March 2014. It’s scope included effects on a range of wildlife but, being sponsored by BCT, bats were a key focus. Full details of the symposium can be found here. This is a short piece I wrote up for the local bat group but I’ve added in the references and a couple of illustrative photographs below!

Artificial lighting is ubiquitous and almost universally accepted – we have street lights for crime prevention and traffic safety; architectural lighting of statues and churches; lighting of industrial sites to allow work to continue 24/7; and light spill from inside houses. Three scary facts which illustrate this are:

#1 Artificial lighting increases globally at a rate of 6% per year;
#2 There are 7.4m street lights in the UK and;
#3 20% of UK energy expenditure goes on lighting.

Variations on this photograph - a satellite image of the earth at night showing the extent of artificial lighting - was the most widely used photograph throughout various talks and rightly so - it serves to show just what an impact we have on the natural environment.
Variations on this photograph – a satellite image of the earth at night showing the extent of artificial lighting – were the most widely used photograph throughout various talks and rightly so – it serves to show just what an impact we have on the natural environment. Photo copyright: NASA

Most bat workers will know of research, such as Emma Stone‘s work in Bristol, which shows that slower flying species such as horseshoe, long-eared and myotis bats tend to avoid light and that lighting their commuting routes can cause severance. Much of the interesting new research at the symposium came from Holland; Herman Limpens looked at whether there are more ‘bat friendly’ lighting spectra and found that amber light caused much less avoidance than white or green light on bats commuting along a dark canal corridor. This was also borne out in analysis of Irish monitoring surveys which found much lower levels of Daubenton’s activity at lit waterway locations. Fiona Matthews from Exeter University put paired static detectors in light and dark locations in a 2km radius around greater horseshoe roosts and found much higher activity levels were recorded in the dark.

Bats can be disturbed when roost entrances are lit: the Life at Night project changed the lighting regimes of churches in Slovenia and achieved significant improvements in both emergence time – horseshoe bats left earlier – and consistency – bats left over a much shorter time period. Kamiel Spoelstra from the Netherlands Institute of Ecology found pipistrelle occupancy rates of boxes to be significantly reduced under white and red light treatments compared with dark.

The ubiquitous Illuminated Church – the subject of the Life at Night talk (photograph from the Life at Night Project Website http://www.lifeatnight.si/en/)

But the picture is not that simple; some species such as pipistrelles and Leisler’s are actually attracted to streetlight. Their speed makes them less susceptible to predators and anybody who has undertaken moth trapping will know that moths gather at light sources, especially attracted to shorter wavelength and UV light. A fascinating talk by Andrew Wakefield from the University of Bristol added a further dimension to this – he found that the avoidance behaviour usually exhibited by moths in response to a bat echolocation call – a change of course or a power-dive where they drop to the ground – is reduced by 60% under lit conditions making them a much easier prey for bats.

The impact of lighting upon invertebrates was widely discussed; for example it was found that larger moths with larger eyes are most attracted to shorter wavelength light and they are drawn in at 6x levels compared with longer wavelength light. This attraction is well known but the implications are rarely considered; Matt Shardlow of Buglife estimated that a third of interactions between moths and light sources would prove fatal to the insects through exhaustion, collision, heat or predation.

The influence which lighting can have upon the relationships between species was a trend which came out in a number of the talks – the impact then can be considered positive or negative, depending upon your perspective. Parasitoid rates on moth eggs were much higher under lit conditions as the diurnal parasitoid gains the advantage. Redshank increase their foraging in lit areas, favouring the redshank (perhaps?). Similarly, a Leisler’s bat can forage more efficiently, but to the detriment of the moths which are preyed upon. Lighting at night disturbs and disrupts the natural rhythms, dynamics and ecological signals.

A peacock butterfly seeking out a dark place to hibernate.
A peacock butterfly seeking out a dark place to hibernate.

One of the last talks of the symposium was from Kate Harrington who found evidence for in-combination effects of artificial light and artificial noise on bats – as the two are so often associated such as from traffic along well-lit roads, the potential for this to modify the natural environment more severely is significant.

Several talks discussed the importance of good design in lighting schemes for new developments – light only where it is required, light as low as required and design cut-offs and cowls to avoid unwanted light-spill onto surrounding habitats. The project along the Thames at Richmond is an excellent example of this – this video shows how the lights respond to pedestrians so that they feel they are walking in a pool of lights whilst all around remains dark. The importance of maintaining dark corridors was also an important part of the London 2012 park design.

The copper beech outside the Guildhall on the High Street in Grantham showing the extent to which lighting is a normal and accepted component of our villages, towns and cities.
The copper beech outside the Guildhall on the High Street in Grantham showing the extent to which lighting is a normal and accepted component of our villages, towns and cities.

But new designs are only going to reduce future problems – as I walked back from Grantham station after the conference I was shocked to see the level of light-spill onto hedges, trees, the River Witham and other suitable foraging and commuting habitat. I had never appreciated how much of an effect our lighting of the environment would have upon the species we share it with. BCT will be putting up the videos of the talks and presentations in due course so keep an eye out for the news of their arrival!

Red-eared Terrapin in Grantham Canal

I had something of a surprise when out walking along the Grantham Canal at the weekend. A friend posted a cracking photograph of a mink on twitter (and now on her blog which you can read here) which was seen along the stretch between Harlaxton and Denton. This is a non-native species and can cause serious damage to the ecosystem through their predation on native species of fish, birds and water vole. However, it is argued that, as these are all food sources for the native otter, the non-native mink is filling a currently vacant ecological niche for a semi-aquatic carnivorous mammal in our waterways. Whilst the grey squirrel competed with the native red in a similar way to the detriment of the reds, there is good evidence to suggest that the re-colonisation of a watercourse by otters will lead to the displacement of the smaller mink and so the native species would win out in the end. Whilst we wait, and hope, for otter to continue their spread through our native watercourses, the mink could be seen as its understudy. They can however cause serious problems in some locations, especially where they prey upon the eggs of sensitive bird species, and eradication programmes are in place in a number of locations to remove them. I have only once seen a mink along the canal, on the stretch by Woolesthorpe some years ago, and was keen to see another.

I was scanning the edge of the canal as we walked along and was taken aback to see a completely different non-native species instead – a red-eared terrapin (Trechemys scripta elegans) basking out of the water on a log! This individual was around 30-40cm which is adult sized. These reptiles, originally from the Americas, were popular pets in the 1980’s and 1990’s following the Teenage Mutant Ninja Turtles on childrens’ TV. They tended to out-grow their confinements and many of the more irresponsible owners simply released them into the wild. They can live for several decades and so this specimen could have been in the canal for a long period of time. The sale of these species does continue however so it could be a more recent arrival.

Red eared terrpin in British canal - Grantham Canal, Lincolnshire, UK

The terrapins feed on aquatic invertebrates and amphibians and so, like the mink, are a cause for concern in British waterways. Whilst the mink is quite able to breed and spread throughout the UK, there is less concern about the terrapins at present – they require around 100 days of >27 degrees or 60 days of >30 degrees for the eggs to successfully hatch and the young to develop which is rarely achieved in a British summer. This puts the terrapin into a different category to the mink – whilst they are not desirable, they are at least naturally controlled by the climate and they should not increase under their own steam. This means that there is not currently a requirement to control them in the wild; rather better controls on the sale of these species should ensure that they do not continue to be a problem once the individuals at large have died out naturally. That said, increased temperatures as a result of climate change could see this whole situation change! A juvenile was spotted Regent’s Canal in London last year and this caused concern that they might have found conditions warm enough to breed in our unusually hot summer.

The individual spotted in Grantham canal may even be the only one present – if no others were released alongside it. There is a record of an European Pond Turtle in the canal from 2006 which may be a misidentification of the same individual I saw, or it could be that this non-native species is also present along the waterway.

Next time you are walking along the canal, keep an eye and you might just spot something unexpected!

Willow flowers (or Vegetable Goslings)

Willows (Salix genus) are one of the earliest flowering tree species in the UK and are a fantastic nectar source for early pollinators such as bumblebees and butterflies. These trees are dioecious which means that there are separate male and female trees which can be distinguished by their flowers. Another more commonly known example of a dioecious tree would be the holly – only the female trees bear the red berries. One of the traditional names for willow flowers was ‘vegetable goslings’ which seems a perfect description to me!

Male willow flowers
Male willow flowers – the bright yellow pollen is on the end of the stamens and this brushes onto the pollinators when the come to drink from the nectar.

The flowers are quite unusual when compared with a simple flower such as a buttercup which follows the classic textbook diagram. Willow flowers are catkins – these are spikes of numerous tiny flowers rather than each catkin representing a single flower. Each of the yellow-tipped spikes in the male flower is one of the stamens and there are generally two or more of these to each individual flower within the catkin – the number varies with species. The same is true, although less easily illustrated, for the female flowers which have two or more stigmas per flower.

Female willow flowers
Female willow flowers – these are much less showy and do not have the yellow pollen of the male flowers. They also provide nectar to attract pollinators with the hope that the previous flower visited will be a male willow of the same species and thus the pollen will be transferred and the female flower fertilised.

The male and female flowers appear at the same time in order that the pollen from the male flowers is able to fertilise the female flowers. The flowers are quite different from one another in appearance and, side by side, it would be easy to assume that a male and a female willow tree were two different species.

Development of male willow flowers
Development of male willow flowers. On the left you can see the red outer scale to the bud which breaks and the catkin emerges from beneath. The first flowers on the catkin begin to open – the red tipped stamens can be seen. The yellow pollen then begins to be produced and finally the bumblebee comes to drink from the nectar and incidentally collect the pollen whilst doing so. This is an early bumblebee (Bombus pratorum) and the willow species is Salix x laestadiana which is a hybrid of goat willow and downy willow.

The willow flowers are an excellent source of nectar for early pollinating species, such as queen bumblebees which have emerged from hibernation and are establishing nests, or the early Nymphalidae butterflies which hibernate through the winter.

Small tortoiseshell butterfly on female willow flower
Small tortoiseshell (Aglaise urticae) butterfly on female willow flower. Note the presence of the nectar source in the centre of the catkin whilst the yellow-tipped stigma is higher. The stigma is where the pollen must reach in order to fertilise the female flower and this design encourages successful pollination which is an incidental rather than intentional act on the part of the pollinator which is only interested in a free feed!
Unidentified solitary wasp on female willow flower
Unidentified solitary wasp on female willow flower – any ID tips would be most welcome! This demonstrates the effectiveness of the design of the female flower – see how the wasp must bend low into the flower to reach the nectar source, so bringing its body (which will hopefully be dusted with pollen from a male flower) into contact with the female stigma.