Saturday, 30 March 2013

Going Native

The global transportation of goods has a long history. As we have moved around the planet so we have transported with us many different plants and animals, introducing them to new regions. Some have been taken unwittingly, stowing away on ships, in timber or in foodstuffs; others have been deliberately introduced to remind us of home.

Within the UK we have seen countless examples where introduced species have gone on to become a problem within the wider countryside; American mink, signal crayfish and Japanese knotweed all spring to mind. There are, however, many instances where an introduced species has simply filled a vacant niche and established itself without having any impact on other species. One of the most interesting aspects of the debate about these introduced species has been the extent to which something is considered native or introduced. Some of the creatures that were deliberately introduced many centuries ago are considered as natives, while recent colonists arriving unaided are sometimes treated as unwelcome invaders.

Our own perceptions of particular species cloud the debate and we even see conservation practitioners arguing with each other about whether or not a species should be controlled. The ruddy duck privides a good example. This species was introduced to Britain by the Wildfowl and Wetlands Trust in the 1950s, when individuals escaped from Slimbridge. An expanding population saw individuals move into Europe, where they came into contact with the related white-headed duck, a globally-threatened species. The solution seemed simple enough, cull the ruddy ducks to save the white-headed duck, but there was stiff opposition from many quarters, including from birdwatchers who liked seeing these birds here in Britain. The West Midlands Bird Club, for which the ruddy duck was a special species, even managed to smuggle a subtle image of the species into their new logo once the ducks profile switched to that of unwanted alien.

For other species the problem comes from uncertainty over whether it is native or not. Our slowly expanding eagle owl population almost certainly stems from aviary escapes and deliberate releases. There is, however, a very small possibility that an Eagle Owl from elsewhere in Europe might reach our shores. This uncertainty is used by some as an argument against culling the pairs breeding here now, even though some bird carry the jesses that reveal their captive origins. You might wonder if it really matters; you might even argue that it is better to accept that our activities will result in introductions and that conservation money is better spent elsewhere. Perhaps the most pragmatic solution would be to remove definitely introduced species as soon as they appear, accepting that other species may be too well established now to manage effectively.

Friday, 29 March 2013

What's going on in the shrubbery?

The dunnocks are much in evidence in the garden at the moment, with plenty of song and display. Known to some readers as the hedge sparrow, the dunnock isn’t a sparrow at all but it does like the cover afforded by hedges and other shrubbery so this sometimes-used name is not completely wrong. The dunnock is an often-overlooked bird, perhaps because of its skulking habits or maybe because of its rather drab appearance and superficial similarity to the more familiar house sparrow. Despite this, the dunnock is a particularly engaging bird with a fascinating private life.

As with many other familiar garden birds, the dunnock maintains a breeding territory that is advertised through song. The song itself is rather melodic and is comprised of a series of sweet-sounding phrases, well worth listening out for. Although most dunnock pairs are monogamous, with one male and one female paired together, some indulge in rather more complicated living arrangements. Instances of polyandry (one female with two males) are rather common, as is polygyny (one male with two or more females) and there are even occasions where two or three males may form a relationship with three or four females. It is thought that such complex relationships develop because male and female dunnocks maintain their own, largely independent, territories during the breeding season. Male territories tend to be larger, so each male territory may overlap with several females.

Instances where two males appear to share a territory are also fairly common, with one male (the alpha male) dominant over the other (the beta male). Although both males may mate with the resident female, the alpha male gets the greater share of the matings. The two males will work together to defend the territory against other males, with both birds singing and displaying when faced with potential rivals.

Such complex relationships have also given rise to some interesting courtship behaviour. Prior to mating the female dunnock will crouch before her partner, quivering her body and lifting her tail. This prompts the male to peck at the female’s cloaca (which is associated with her sexual organs). The repeated pecking causes the cloaca to enlarge and this is then followed by a series of pumping movements by the female which serve to eject some of the sperm from any previous mating. It is thought that this ejection of sperm increases the chances that the current male will sire a greater proportion of the offspring. Such behaviour surprises many people and may even be enough to make them blush, especially if they have asked the question as to why dunnocks may sometimes peck each others’ behinds! It is surprising what goes on in our gardens!

Thursday, 28 March 2013

Changing times for dragonflies

Last summer was, by just about every measure, a poor one for our wildlife. Bird populations took a hit from a poor breeding season, butterflies were notable by their absence and many of our invertebrates fared badly under the cold and wet conditions. Such poor summers are, one would hope, the exception rather than the rule, so there is the opportunity for things to bounce back if they have a better breeding season this year. It is important, however, to view such short-term impacts against the long-term pattern of a changing climate and increasing pressures on the land. Some species will benefit from a changing climate but others will lose out and there is already evidence of differences in how well particular species, or groups of species, are likely to fare.

As a group, dragonflies appear to be doing well and they may be one of the winners from a changing climate. A number of species are expanding their breeding range northwards across Britain and others are in the process of colonising our region. Species like the small red-eyed damselfly, which first reached Britain in 1999, are now well established and spreading. The southern emerald damselfly, which exhibited a major influx at Winterton last September and which has been recorded from the site in six of the last 13 years, was noted egg-laying here in 2012. It has already bred at sites elsewhere in south-east England, most notably at Cliffe in Kent. The willow emerald is another recent colonist, now established across parts of Norfolk and Suffolk.

There are several other dragonflies that reach our shores from time to time, originating from populations breeding elsewhere in Europe and often far to the south. Such arrivals underline the dispersal powers of these often robust insects and the pattern of migration exhibited by some species. A good example of this comes in the form of two Suffolk records of large white-faced darter from 2012. This species has a relatively southern range compared to related species, and most populations tend to be rather small. An unexpected and rather large movement of this (and related species) was noted in 2012, with individuals recorded from sites across north-west Europe, including the British records from Dunwich Heath and Landguard. Such movements are likely to result from a good emergence, coupled with favourable weather conditions, that deliver individuals to areas beyond their normal range. If individuals arrive in good numbers at sites where suitable habitat is available then there is a chance that breeding may take place and the species become established. Under a changing climate, warmer conditions in Britain may further favour the establishment of more species with a formerly southern distribution, so it is very much a case of watch this space.

Wednesday, 27 March 2013

In pursuit of spring

The other weekend, a series of meetings and a conference took me south through the Chilterns, west to Reading and beyond. Any journey south that is made at this time of the year has the lure of spring about it. Spring is more advanced on the south coast than here in East Anglia; the buds more strongly swollen and the spring flowers further into bloom. It feels as if you are passing through time, rather than space.

Driving through mixed arable land, I passed many a clump of trees that hosted a rookery, with birds in attendance and standing sentinel over nesting attempts that already well underway. Skirting further south I drove through Gilbert White’s Selborne, dominated by its beech hanger and the surrounding downs. On another day I would have stopped here, walked the zig-zag path up the hanger or tacked across the fields towards Noar Hill. There is a strong sense of history in this landscape, the feeling that it has not changed quite so much as to now be unrecognisable to its former inhabitants.

The poet and writer Edward Thomas made a not dissimilar journey almost exactly a century ago. Heading west out of London with his bicycle, Thomas set out ‘In Pursuit of Spring’ documenting the landscape, its people and its sense of place. Although sometimes portrayed as a piece of nature writing, Thomas’s book is, in reality, something rather different. The wildlife described in his account is not central to the text. Instead it is part of the backdrop, contributing to the sense of landscape and place, working its part alongside names marked on the gravestones of the churchyards visited or the character of the buildings that sit within the folds of countryside that are passed.

Thomas’s journey is also a personal one and through his words you can discover something of the man and his reactions to a landscape that was undergoing a period of change. There are passages where Thomas laments what has been lost, something that I suspect is common to most writers on landscape, but these are balanced by moments where the joy of being at one with the landscape pushes through strongly. Landscape has this amazing ability to take hold of us and to lift our spirits. For me the sight of these springtime rookeries is a case in point; they are so characteristic of spring in the south of England, reflecting the wider landscape within which they sit. To see such a rookery can transport me immediately back to my childhood, delivering me to a landscape that skirts the downs and which appears timeless in its associations. This remains the landscape of Edward Thomas and those writing before him.

Tuesday, 26 March 2013

A rare glimpse of Fallow Deer

The sight of three fallow deer in the forest the other morning was my first encounter with these elegant creatures for many months. Of the four species of deer to inhabit this part of the forest, the fallow is the one that I see least often; roe and Muntjac provide almost daily sightings and I probably stumble across the red deer once or twice a month. This suggests that the fallow either occur at low density in this particular area or, more likely, they are occasional visitors from elsewhere.

The sighting comes in the week after the launch of a report highlighting that there are too many deer in our forests, their numbers having increased to a point where they are damaging the nature of the woodland ecosystem. A particular problem comes from the browsing of the ground and shrub flora, to the extent that many of our woodlands now show a clear ‘browse line’ below which few plants are able to grow. This has knock-on effects for our insects, small mammals and ground-nesting birds. Increasing deer numbers have, for example, been linked to the loss of breeding Nightingales from many of our woods.

Fallow is the most widespread of the British deer species, being present on a number of offshore islands and most of the mainland – though it is absent from our uplands. A form of fallow deer was present in Britain historically but this became extinct following the last glaciation. The species was then introduced by the Normans and hunted in the 2,000 plus deer parks and hunting forests that were established from the 11th to 14th centuries. Over time the fallow deer colonised the wider landscape, later becoming the deer of choice in most of the landscape parks associated with our larger stately homes.

Although woodland is an important habitat for fallow deer, providing winter food and year-round cover, these particular animals tend to feed in more open situations. Forest rides, woodland edges and grassland habitats are well-used. Some populations thrive within our more arable landscapes, feeding on crops and margins and resting up in small woodlots. That fallow deer are grazers rather than browsers is very evident when you watch them in a parkland setting like Holkham.

I tend to think of the local fallow deer as being part of the forest, much like the roe and red deer that are more truly native. In reality they are the result of deliberate introduction, a species added to the landscape for our own ends. We have always managed our fallow populations and this is something that will need to continue if we are to limit their impact on the woodlands systems with which they are associated.

Monday, 25 March 2013

Breckland speedwells

Breckland, the sandy district that straddles the Norfolk/Suffolk borderlands around Thetford, is the British counterpart to the steppes of Eastern Europe; or rather it was, before much of it was covered with conifers and ‘improved’ for agriculture. Hot, dry summers and cold winters with late frosts typify the area and shape the community of plants that the light Breckland soils support. A number of these plants are nationally rare, squeezed into the margins by our activities. Others are now described as ‘nationally extinct.’

A feature often shared by these plants, other than their rarity, is their small size. These are the sorts of plants that you have to get down on your hands and knees to see, perhaps using a magnifying glass to truly appreciate their delicate beauty. Some have been known to plant enthusiasts for centuries but others are more recent discoveries, previously overlooked. Fingered speedwell, for example, was discovered at Thetford in the 1600s by Thomas Willisell but Breckland speedwell was not discovered until 1933, when J E Lousley and A W Graveson stumbled across an unknown plant near a track at Tuddenham Gallops. The chosen name of Breckland speedwell was, perhaps, a little unfortunate as the species was later found growing in Oxfordshire. Today these two speedwells remain rare plants, still to be found on disturbed ground in the Thetford housing estate that now covers one of their former sites. I suspect that many of the householders may been maintaining these fragile populations in their flowerbeds where they are overlooked as ‘weeds’. If only they knew.

Not all of Breckland’s rare plants are small. The military orchid is large and showy and it is amazing to think that it remained overlooked, growing quietly in a chalk pit near Mildenhall until 1954 when it was discovered by Mrs M Southwell. The military orchid occurs as a native at just two other sites within Britain, making the colony at Mildenhall of great importance.

At the time that many of Breckland’s rare plants were being discovered there were many other species that would have been viewed as being common and widespread. Some of these are species that we would now regard as rare, their populations having undergone massive decline as a result of changes in land management, notably land drainage and the intensification of agriculture. Species like tower mustard, fine-leaved sandwort and corn chamomile have all suffered at our hands. There is a glimmer of hope for some of these plants, however, with the prospect of seeds sitting dormant within the soil, waiting for the ground to be disturbed and their chance to germinate. Others have been introduced to nature reserve sites, where management can be directed towards their needs.

Sunday, 24 March 2013


Thanks to a web cam I’ve been able to keep an eye on a pair of tawny owls that has taken up residence in a nest box situated within a large suburban garden. This particular pair is somewhat early in its timing this year, well ahead of most other tawny owl pairs nesting in the UK. The female laid her first egg in mid-February, her second following a few days later on Saturday 16th. I know this because during the early days of laying she would vacate the box just as it was getting dark, presumably to hunt, preen and stretch her wings, leaving the eggs clearly visible in the bottom of the nest box.

While our familiar songbirds, like tits and finches, tend to lay one egg per day, tawny owls lay one egg every two to four days, a pattern seen in our other breeding owls. The interval may vary depending on the weather conditions and it is usually longer between the last two eggs than the first two. Tawny owls usually start to incubate with the first egg; this is different from tits and finches, which usually wait until the clutch is complete. This means that tawny owl chicks do not all hatch at the same time, but emerge over a number of days to leave a clear hierarchy of ages. This is what we biologists call asynchronous hatching.

Asynchronous hatching is thought to be an adaptation, allowing owls and other birds of prey (who also show this behaviour) to cope with years when food supplies are poor. If all of the young owlets were the same age and size, then a shortage of food would probably see the loss of the whole brood. Since older chicks always secure food first, a hierarchy of ages ensures that it is the youngest (and weakest) chick that succumbs first when times are tough. This acts to reduce the brood size downwards towards a level that is better supported by the resources that are actually available.

This may seem particularly cruel but, as a strategy to produce as many young as the conditions can support, it is a successful one for the owls to adopt. The strategy is even more obvious in the barn owl, where a larger clutch of eggs tends to be laid and the reduction in brood size can be more dramatic. Being born so early in the year may prove challenging for the young tawny owls. However, if they fledge from the nest successfully they should gain independence at about the time that the abundance of food reaches a decent level, supporting them as they learn to hunt and to fend for themselves.

Friday, 1 March 2013

Red in tooth and claw

There have been a few stories in the local press of late about the otters now re-established on our local rivers. These stories have centred on the loss of koi carp and other ‘ornamental’ fish from unprotected ponds in gardens that back onto the river. In each case, the owners’ anger is clearly voiced and directed towards the perceived villain of the piece, a marauding otter. One couple even went so far as to drain their pond and then blame the otter for the resulting loss of wildlife. Interestingly, since introduced fish have been shown to lower the wildlife value of a pond, the best thing to have done would have been to have left the pond fish-free and to watch the levels of invertebrate and amphibian diversity increase.

My reaction to such stories is one of frustration; how can people seek to place the blame elsewhere simply because they fail to understand that nature is ‘red in tooth and claw’? If you stock a small pond, lacking in cover, with lots of fish then of course it is going to prove attractive to a passing predator. If you are going to keep exotic fish in such an artificial manner, then the fault lies with you and you only have yourself to blame. 

Such stories underline one of the fundamental problems with human society in a wider context, namely that everything has to be about us. We find it incredibly difficult to accept that other creatures have an equal right to this planet and its resources. We take little interest in how our activities impact on other species but kick up a fuss when the boot ends up on the other foot. It is something of which we are all guilty, perhaps through the sprays we use on our vegetables to combat aphids and caterpillars, through to the intolerance of the wasps that nest in our roof spaces or the moss that seeks to grow within our lawns.

We need to engender a shift away from the narrow perspectives of our self-centred lifestyles and reconnect with the natural world in ways that ensure deeper, more long-lasting and respectful bonds. This is not going to be easy. Even our nature reserves – where much of our current connection with nature takes place – are flawed by the underlying sense that they are the only place where nature is allowed and that the nature to be found elsewhere is either fair game, in the wrong place or on the run.

Fortunately, the anger of the few that is directed at our otters is balanced by the positive engagement that others feel when they see these stunning creatures take back ownership of the rivers and ponds.