Wednesday, 30 May 2012

Nesting course

The Hindhead Commons in the Surrey Hills are where I cut my teeth as a young naturalist. This weekend I am back here, helping to lead one of the BTO's Nest Recording Courses. The courses provide the opportunity for people to develop or refine the skills needed to find and monitor bird nests for this key scheme providing information on breeding success and productivity.

Scrubby heathland can be a hot, dusty and difficult place to work but it holds some very special birds, including Tree Pipit and Woodlark. These two species can be a challenge for the nest recorder, wary around the nest and usually nesting in wide areas of uniform habitat. This means watching from a distance when off-nest birds return (visits to the nest can be 40 minutes or more apart, even when feeding chicks) in the hope of pinning down the nest location.

Woodlark nesting habitat in Surrey
With the Woodlark listed as a protected species we are operating under a Schedule 1 licence. The nest itself is placed on the ground, often in heather or other low vegetation, and it is essential to watch where you put your feet and to make sure that you do not damage the vegetation as you move around. The Woodlark pair that we are watching a feeding under the shade of a solitary tree, taking their time and giving no indication that they might have young in a nearby nest. Finally, after just under an hour of patient watching, they take to the air and head a hundred metres east, the lead bird (invariably the female) dropping down into a patch of light vegetation. Over the next 10 minutes we watch her walk towards what we hope will be the nest, though she often disappears from the sight. The important thing is that she is carrying food, as is her mate who has also landed nearby.

There is a crucial moment where she reappears from behind a tussock without the food she was carrying, a decent indication that she has visited a nest and fed chicks. We give it a few more moments and then walk towards the point. One of the difficulties of watching birds back is that distances are foreshortened and two tussocks which might seem close together turn out to be many feet apart. With Tony watching for a different angle, we are able to narrow the search down to a few feet of heather. Even so, the nest is well hidden (see below).

Woodlark nest - can't you see it?
 It is then a case of carefully working through the vegetation to reveal the nest itself and the young Woodlarks within. You would think that the adults would have to make visits more frequently, but such is the abundance of prey in this good weather that a few early morning feeds have packed in plenty of food and the adults can now be more laid back in their approach. These young a too young to ring but Tony will return in a few days.

Woodlark nest with young

Saturday, 26 May 2012

The Land of the Rabbit

You often encounter rabbits when you are out and about in the Norfolk countryside. The dry, free-draining soils of the Brecks are particularly well suited to their needs and it is no surprise that I see so many rabbits on my travels. There is a long history of the rabbit in the area and it would be fair to say that the rabbit has shaped the Breckland landscape and, at times, driven its economic fortunes.

Breckland was once a centre for the production of rabbits, with huge warrens maintained on many of the estates and an industry producing felt that continued through into the 1950s (and the arrival of myxomatosis). The rabbits arrived soon after the Norman Conquest and the light soils of Breckland, although poor for crops, were ideally suited to these burrowing lagomorphs. Initially many of the warrens were operated by landowners but from the 15th Century most were leased to professional warreners. Their legacy can be seen in some of the local place names, for example Thetford Warren, and in the ruined lodges that once housed the warreners.

Needless to say, many rabbits escaped from their warrens and damaged both crops and the landscape, altering vast tracts of land with their burrowing habits. The scale of the rabbit’s impact can be seen in the writing of the time. Gilpin had called Breckland ‘the land of the rabbit’ and the fifth Earl of Albemarle, also writing in the 1800s, described the Breckland region as ‘a mere rabbit warren’, noting that it still went by the name of ‘the holely [Holy] land.’ Walk across a large and long established warren today and you soon learn how difficult the going can be; with each step you run the risk of sinking a leg into a tunnel and turning an ankle.

Over time the rabbit industry gradually faded, as farmers enlightened by new agricultural practices came to regard the rearing of rabbits as a wasteful and damaging practice. The rabbit continues to make a living in Breckland; sometimes it is cast as a villain, eating farmland crops, and sometimes as a useful tool for conservation, maintaining the short Breckland turf that favours rare insects and birds like the stone curlew. One of the best places to sit and watch rabbits is the Norfolk Wildlife Trust reserve at East Wretham. I find that watching rabbits changes your attitude towards them. To see their social interactions or watch their response to a passing stoat shifts them away from the image of a brown blur bolting for cover to a creature of interest and worthy of study. I am certain that the rabbit will continue to play a role in our countryside for generations to come.

Friday, 25 May 2012

Looking out for bees

On the warming days of spring one becomes aware of the increasing numbers of insects that are on the wing. While a month or so ago it will have been the large queen bumblebees that caught the eye, now many other species can be seen. In the garden, early nectar sources like lungwort, bugle, dandelion and ground ivy are worth watching; more widely, it is the blossom of blackthorn, hawthorn and apple that are worth a glance.

Many of our smaller bees are easily overlooked, not just because of their small size but also because they can prove quite a challenge when it comes to identification. As with the majority of insects these small bees usually lack an English name, a further factor hindering their accessibility to a wider audience.

One of the biggest groups is made up of the 67 or so species that belong to the genus Andrena. These are solitary bees that nest in the ground, hence the common name of ‘mining bee’ sometimes used to describe them. Each female has her own nest, accessed via a tunnel and from which radiate several lateral burrows. Each of these short burrows ends with a nest cell, or small cluster of nest cells, lined with a wax-like substance and holding an egg. Each cell also carries its own ball of pollen, which will provision the larva that emerges from the egg. Many of the Andrena species are rare or have a restricted distribution, but a few are widespread and may be encountered across a range of habitats. Andrena bicolor, for example, is a common species that can often be found nectaring at bramble. It has two broods each year, the first active from March until early June and the second, which is a smaller brood, on the wing from late June through into August.

As is the case with many solitary bees, the nest of Andrena bicolor is sometimes lost to kleptoparasitism (literally, parasitism by theft). In this case, it is another species of small bee that enters the nest chamber and deposits its own egg. The resulting larva kills the egg or larva of the host with its large, sickle-shaped jaws, before eating the ball of pollen.

Other solitary bees are larger in size, approaching the size of a honeybee, and more accessible to the casual observer. Some can be identified from a photograph, perhaps posted on the i-spot website, while others may require a specimen to be sent to an expert. It is possible, however, to identify many species down to the family or genus level, something that might spur you on to get better acquainted with this group of insects. There are even courses to help you improve your identification skills.

Thursday, 24 May 2012

The hazards of migration

The hazards of migration were brought home to me the other day by a photograph that had been sent in to our offices. The photograph showed a large number of swallows and house martins, all huddled on the narrow ledges of a building. These birds, newly arrived in the west country, had flown into bad weather and so had sought what little shelter they could find in order to sit out the heavy rain that was falling.

More widely this spring, we have seen birds held up on migration by poor weather in the Mediterranean. A blocking weather system had halted the migratory journey and forced the birds to sit out the bad weather, while using up vital reserves. At least one of the BTO’s satellite-tagged cuckoos seems likely to have succumbed to the weather. It was charted heading North on its spring migration but ran into bad weather in southern Spain; there it stayed, the signal from the tag suggesting that the bird had died.

You might think that migration was a fairly routine affair for birds, like swallows and martins, able to feed as they went along. Research suggests that even these species have to fatten up ahead of their migration, taking on reserves to help get them across barriers like the English Channel, the Mediterranean and the Sahara Desert, where feeding opportunities are presumably scarce. It is harder still for those species that do not feed on the wing and which have to stop-over to take on more ‘fuel’ at various points along their route. These ‘stop-over’ sites are important and many will be used on a traditional basis. For example, two of the BTO’s cuckoos, taking an easterly route, stopped at the Po Delta in Northern Italy on their way south. This suggests that we should look in more detail at the region to establish its role as a stop-over site for cuckoos and other migrants.

Even when the birds reach their destination they may face problems. There is a pressure to arrive early on the breeding grounds in order to get the best territories, but if you arrive too early then the weather may prove unsuitable and you may die. This year, the cold and wet spring has caught many birds out and even resident species, like tits, seem to be struggling. This time last year, we had large numbers of reed warblers and whitethroats on well-advanced nesting attempts; this year they have only just started to get going. Of course, it is only at the end of the year that we will really know just how poor the season has been. Until then, it is fingers’ crossed for some better weather.  

Wednesday, 23 May 2012

Living below ground

When you think of blue tits and great tits you tend to think of familiar garden visitors, species attracted to bird tables and wooden nest boxes placed on the trunk of some garden shrub or small tree. Of course, many more of these birds make a living in the wider countryside, feeding on defoliating caterpillars in woodland and nesting in natural cavities.

Within woodland, natural cavities occur in many shapes and sizes, and only some of these will prove suitable for hole-nesting birds like the tits. There can be competition for natural cavities and it is perhaps unsurprising to discover that great tits will oust blue tits from suitable cavities and that, in turn, blue tits will oust coal tits, such is the dominance hierarchy that exists. The size of the entrance hole and the location of the cavity influence the degree of competition, largely because of the size differences between the three species. Being the smallest of the three, the coal tit can use cavities with a small entrance hole, cavities into which the other two species cannot squeeze. In particular, coal tits will use those cavities that occur low down, often no more than a narrow slit opening up into something a little larger within. Great tits require the largest entrance hole and blue tits fall in the middle.

The other day we were out in the forest, leading a group of volunteers learning the art of nest recording, when we came across two good examples of natural cavities used by nesting tits. The first was a coal tit nest, placed deep into a ‘snag’ line, the row of conifer stumps that is pulled together when a block of commercial plantation is harvested. The parents were busy feeding the chicks, taking in food and carry off faecal sacks. These sacks keep the nest clean and remove tell-tale droppings that might give the nest location away to a predator.

The great tit nest was more unusual (at least for a great tit), the birds having found a cavity in an old tree stump that disappeared down below ground level. We only stumbled across the nest when the sitting female was flushed by our approach – great tits usually sit fairly tight when on the nest. In her absence we were able to use a boroscope – essentially a tiny camera on a long and flexible cable of the type used by plumbers – to peer into the darkness. There, on the small video screen, was the image of six eggs in a neat nest cup. This nest would be fairly secure from most predators, though it might be at risk from a weasel or from flooding but with luck it should survive.

Tuesday, 22 May 2012

A scream from above

I hear them from inside the house and feel a spark of excitement. In an instant I am out of the door and looking up at the dark, paynes grey-coloured sky. There they are, the curve of wings and the tiny streamlined bodies;­ the swifts are back. These are not the first swifts that I have seen this year but they are the ones that matter. These are the birds that will take up home in traditional sites along this urban street and these are the birds that will be ever present over the few short weeks that define our English summer. The swifts that I saw earlier in the year, hawking over flooded gravel pits on damp, overcast days, were transient pathfinder birds, passing through to breed somewhere else. It is ‘my’ swifts that matter and it is ‘my’ swifts that I await with such strong anticipation.

The hold that these summer visitors have over me is a relatively new thing; they are not a species with which I was closely associated in my rural childhood and it has only been since I moved into this small market town that they have come to mean so much. I think it is the coupling of their brief summer visitation with the knowledge that they have covered many thousands of miles, roaming over African landscapes, that creates a spell of great strength. They define my urban summer and when they leave and the sky falls silent, so I feel a sense of tremendous loss.

I know that I am not alone in the close connection that I feel with these birds. Phone calls and emails from worried friends, asking “where are the swifts; have they not arrived this year?”, tell me that others too wait anxiously for their arrival. The poet Ted Hughes captured this sense of nervous anticipation in one of his poems, delivering a great shout of relief once the birds appeared in the skies above his urban scene.

I like to imagine the journey that these tiny birds have made, to picture the different landscapes that they must have flown over, and the upward glances of those people who share ‘my’ swifts when they are elsewhere. The swifts spend so little time here that you might consider it wrong to think of them as ours, but they choose to make their homes here and to rear their chicks, so maybe it is a natural assertion to make.

Each morning, as I step out, I know I will glance up to the sky to check that the swifts are there, to take comfort in that knowledge and to hold it with me throughout the rest of the day. It feels good to have them home.

Monday, 21 May 2012

A solid lining

I can see the nest ahead of me, wedged between the flat panel of a fence and a horizontal limb of blackthorn. The nest itself is a melon-sized construction of moss, grass and dead leaves, the work of a blackbird or song thrush. It is only when I get to peer inside that I will be able to tell which of the two species is responsible for its construction. The problem for me, however, is that there is a thick stand of blackthorn between me and the nest, the branches characterised by long thorns which are quick to impale, the tips breaking off and leaving a painful reminder buried in your skin.

Having weighed up the situation, and keen to add this nest to the list of those thrush nests being monitored locally this year, I work out that I can crawl ‘commando style’ under the lowest branches and, with a good deal of care, get to my feet within a metre of so of the nest. Armed with a video borescope, of the sort used by plumbers to check the inside of narrow pipework, I should be able to get a view inside the nest.

In addition to being able to record the nest contents, I will be able to make a firm identification of the species involved. The eggs of blackbird and song thrush are different but equally useful is the difference in nest construction. In blackbird, the outer foundation of moss and grass is followed by a lining of mud to form a cup, inside which is a final layer of finer material. In song thrush, the foundation of moss is followed by a layer of rotten wood that has been smoothed and bonded with saliva. There is no further lining, the song thrush laying its eggs directly onto the avian ‘chipboard’ that it has created. It is thought that the solid lining may reduce the impact of nest parasites but if this is the case, why isn’t the behaviour more widespread? Surely, there must be some additional cost of dispensing with a soft lining.

Once in position, I extend the snake-like cable of the borescope, camera at its tip, and inch it through the thorns to a position just above the nest. The small video screen reveals four bright blue eggs on a smooth and solid lining; it is a song thrush after all and a valuable record for the BTO’s Nest Record Scheme. I reverse the process and slowly inch my way back out from under the tangle of vegetation, before making a note of the nest, its location and its contents. I’ll be back out this way in a week, when another check on the nest is due.