Frogs hop into spring

It often surprises me how seemingly unfussy frogs are with their spawning grounds. I have seen them in road ditches in Scotland and even taking to an old ceramic toilet buried and filled in a previous garden of mine. On the corner of our village road is a rather sad, shallow pond – or more accurately a large muddy puddle choked with leaf detritus, rubbish and even occasionally the odd fridge. Earlier this month however, ‘Top Town Pond’, as it is called locally(1), was choked by something very different and far more welcome - by frogs making their annual frenzied return and all the more obvious in the few inches of water.

So what makes them choose what seems at face value to be a less than attractive location for their spring romance and productivity? The first evidence that I have noted is that there are always small fish present, even in the height of summer when you might expect this pond to dry out. According to locals the pond is fed by continually by a spring from the nearby Dumble, “a stream which has formed a deep wide channel in the clay that is quite out of proportion to the amount of water normally carried”(1). So although the pond more than halves in volume in hot weather, it never completely dries out making it a safe haven for tadpoles to complete their aquatic life cycle. Another factor is the age of the pond - Many amphibians are loyal to their birthplace, potentially using a number of sensory mechanisms to return each year, such as; odours of ponds, landmarks, the positions of sun, moon and stars, and the earth's magnetic field (2). This pond has certainly been there for a long term, and indeed perhaps its presence determined the location of the Pinfold itself as in times past it served to quench the thirst of stray cattle that would be temporarily placed there awaiting their owners to reclaim them(1). Of course the dramatic decline in ponds over recent decades has meant that our amphibians have had to become less fussy – why else would they use my old toilet!

The pond has now returned to relative calm whilst the clumps of abandoned jellied eggs slowly warm in the rising spring temperatures. In a few weeks however the shallow waters will be churning again to movement of black tadpole shoals overshadowing the resident minnows.

(1) The Westhorpe Dumble Heritage Trail (see http://www.newark-sherwooddc.gov.uk/ppimageupload/Image81741.PDF) (2) Sinsch, U. (1990) Migration and orientation in anuran amphibians. Ethology Ecology & Evolution, 2 (1): 65 - 79

Blackcap warming to English winters

During a recent visit to my parents in Ledbury, Herefordshire, I was delighted to see the distinctive Blackcap (Sylvia atricapilla) frequently feeding from their birdtable. This warbler is probably the easiest to identify with distinctive skull caps, black in males and a chestnut brown in females. Like many other warblers, the Blackcap is a summer migrant to Britain. However since the 1960’s it has been increasingly seen staying over during the winter, particularly in southern England - I have never seen this species where I live in Nottinghamshire. Why have a growing proportion of Blackcaps decided not to migrate during the harsher winter conditions?

Migration clearly requires a high cost to the ‘traveller’, in terms of energy and ‘in-flight’ hazards. If the benefits of staying put over winter outweigh those of migration, you might predict that some would be tempted to stay. It would appear that the Blackcap with more eclectic tastes than other warblers more reliant on insects, has taken advantage of the growing bounty found on English birdtables. It has also been proposed that it is also a good example of how some wildlife is responding to climate change and warmer British winters, which might well lead eventually to complete residency as temperatures continue to rise (Pulido & Berthold). So, although many households welcome this addition to their gardens in winter, its increasing presence may also be a warning signal of continued climate change and less welcome impacts on other wildlife.

I guess it won’t be long before the Blackcap will start to turn up more frequently at birdtables in the Midlands and further North.

Pulido, F. and Berthold, P. (2010) Current selection for lower migratory activity will drive the evolution of residency in a migratory bird population. PNAS, 107 (16): 7341-7346

This antisocial poisonous plant clone is not for sale

I took a stroll in our local woodland yesterday and was surprised to see how much had changed in a couple of weeks. Everywhere new green vegetation is pushing through as the snowdrops fade. Most notable are the Lord’s and Ladies (Arum maculatum) and Dog’s Mercury (Mercurialis perennis). Interestingly both of these species are reputed to be poisonous to animals, perhaps defending themselves as early emergers from the onslaught of grazing. However for Dog’s Mercury the evidence appears limited and contradictory. Watson (1998) describes suspected poisoning in cows, but such reports are rare and there are reports of animals happily grazing on the plants such as Muntjac deer. Interestingly it is also used in remedies for medicinal purposes, such as the ointment, ‘Wound-Care’, used to help accelerate wound healing (Weleda, 2009).

Dog’s Mercury is dioecious (=two forms) with clearly different male and female plants, in particular the floral parts (the plants in the image are male, showing catkin like spikes emerging from leaf axils - Rose, 2006). However this species expands mainly asexually by vegetative propagation, with rhizomes extending underground and sending up frequent aerial shoots. This produces large single sex clonal stands which appear to remain quite distinct, rather than mixing with adjacent ones (Wilson, 1968 – cited in Jefferson, 2008). Have a look and observe that most patches are distinctly male or female. Improved light conditions (such as canopy openings in woodlands) appear to favour male plants (Vandepitte, 2009b) which may exaggerate their separation from females.

Although it is a widespread and common plant in woods and shady places, its distribution appears to be limited by a strong affinity to ancient woods in Britain (Peterken & Game, 1981). There is also evidence of local declines through factors such as increasing deer browsing (Hall, et al. 2004), coppicing and other disturbance that opens up woodland canopies, bringing increased competition from other plant species. So with poor mobility and growing threats, it is probably declining gradually in parallel with the loss of older and precious ancient woodland (Grimes et al, 2007). So please look again at this apparent modest plant and see it as an indicator of the health and heritage of our woodlands which should not be put up for sale to the highest bidder.

Hall, J.E., Kirby, K.J & Whitbread, A.M. (revised 2004) National vegetation classification field guide to woodland. Joint Nature Conservation Committee.
Grime, J.P., Hodgson, J.G. & Hunt, R. (2007) Comparative Plant Ecology: A Functional Approach to Common British Species, 2nd ed. Colvend, UK: Castlepoint Press.
Jefferson, R.G. (2008) Biological flora of the British Isles: Mercurialis perennis L. Journal of Ecology, 96: 386-412
Peterken, G.F. and Game, M. (1981) Historical Factors Affecting the Distribution of Mercurialis perennis in Central Lincolnshire. Journal of Ecology, 69 (3): 781-796.
Rose,F (2006) The Wild Flower Key – How to identify wild flowers trees and shrubs in Britain and Ireland. London: Penguin Books Ltd
Vandepitte, K., Roldán-Ruiz, I., Leus, L., Jacquemyn, H. and Honnay, O. (2009b) Canopy closure shapes clonal diversity and fine-scale genetic structure in the dioecious understorey perennial Mercurialis perennis. Journal of Ecology, 97:404–414
Watson, P.J. (1998) Suspected dog’s mercury (Mercurialis perennis) poisoning in cattle. Veterinary Record, 142 (5): 116–117.
Wilson, J.F. (1968) The control of density in some woodland plants. PhD Thesis, University of Lancaster, Lancaster, UK.
Weleda (2009) Wound-Care [online]. http://usa.weleda.com/our-products/shop/wound-care.aspx [Accessed December 17th 2009]