Friday, 22 July 2011

Barn Owls have a mixed season

It is great to be out ringing Barn Owls again. I have worked on Barn Owls for nearly 20 years and I have yet to get tired of the summer round of nest box checks and ringing sessions. Admittedly, it can be a messy business. Barn Owl nests are not the most hygienic of places; the young have a tendency to poo on you and the birds sometimes carry flat-flies, unpleasant parasites that seem ever willing to jump ship and lodge themselves somewhere about your person! I’ll never forget one summer evening where, sitting in a pub with friends after a day of ringing Barn Owls, a flat-fly emerged from a friend’s hair, buzzed around the table and then landed on the blonde sat at the neighbouring table. She didn’t notice it and my friend was too embarrassed to tell her!

Barn Owl site in Lincolnshire
It appears to have been something of a mixed season for the Barn owls this year, with many pairs on two chicks and others just scraping the three that is the national average for brood size at fledging. Conditions elsewhere are better, with fours and a single five but without any of the larger broods that you tend to see most years. Some indication of food availability can be seen from the cache of small mammal prey items that is often present at the nest. The best of those seen the other day had seven Field Voles and three Water Voles, the latter an uncommon food item these days (primarily because the Water Vole population is not what it once was). The presence of a slowly meandering river within fifty metres of the nest box explained why these particular owls had been able to find the Water Voles so readily.

Prey caches across the sites were not too bad, perhaps suggesting that it might have been earlier in the season that the owls were struggling to find food. We know that the condition of the adults going through the winter will influence their chances of breeding the following year and it is possible that clutches sizes were below average this spring.
Young Barn Owl
Barn Owls have a strategy for coping with the unpredictable nature of their food supply. They incubate the eggs from when the first is laid. This means that each egg hatches roughly two days before the next one, producing a brood of chicks whose ages can vary by up to two weeks. Since the young compete for food, it is only when the oldest chicks have had their fill that the youngest get theirs. If times are hard then the youngest chicks will die, leaving the remaining chicks with a greater chance of survival. Nature can be cruel but is always resourceful.

New Bumblebee puts in an appearance

The bumblebees are one of those groups that I have never entirely got to grips with. Given their appearance, with their bands of colour, you might expect them to be rather easy to identify. This, however, is not the case, as some species pairs can look surprisingly similar. This is compounded by the fact that some of the species have different colour forms and all of the species tend to be on the move for most of the time. The key to identifying bumblebees is to invest in a handnet and a large plastic tube in which the bee can be place so you can look at it with a hand lens. I push a small tissue into the pot, gently confining the bee to the end of the tube where I can then see all of the key features.

The other important thing when it comes to identifying bumblebees is to determine the sex and caste of the individual you are looking at; is it a queen, a male or a worker (the latter being absent in the so-called Cuckoo bumblebees)? Telling males from females takes a bit of practice. Although not entirely reliable, male bumblebees usually have some pale hairs on the face, while those of the female are usually black. More reliable, however, are differences in the antennae; females have longer antennae, made up of 13 segments, while the shorter antennae of the males have twelve. A final thing to look at is the shape of the tip of the abdomen. In males this is rather blunt and round, containing the reproductive apparatus, while in females it contains the sting and is more pointed.

The different bumblebees can be grouped according to some basic colour patterns, the colour and positioning of which are the key feature to examine. However, the resulting groupings often contain more than one species (often a single common one and several rarer species) and then you have to look at other features. One of the easiest species to identify, at least in my experience, is the Tree Bumblebee. This species sports a ginger-brown unbanded thorax, a mainly black abdomen and a white tail. Judging by the number I see foraging on the plants at work, I reckon we have one or more healthy colonies nearby and I occasionally get them in the garden at home as well.

The Tree Bumblebee is a very recent colonist, first recorded in the UK in 2001 when an individual was found in Wiltshire. Since then it has spread across much of southern England, where it often nests above ground, sometimes favouring nest boxes erected for birds. Daughter queens are on the wing at the moment so do keep a look out for them.

Thursday, 21 July 2011

Nesting season nears its end for most

It feels as if we are on the home straight as far as our nest monitoring is concerned and, as is usual by this time of the year, we are all starting to flag a bit. It has been something of a broken season for me, with less time in the field because of work pulling together a field guide to monitoring nests. Mind you, my involvement with the book has also enabled me to see nests that have been new to me. It has also been a fantastic opportunity to learn from the real experts in this field, discovering the tips and tricks that can help you pin down the location of a nest so that you can then monitor its progress and complete a nest record card. The information contained on these cards is used by the BTO ( to inform conservation practitioners and Government as to the changing fortunes of our breeding birds.

As such, it was good to be back out in the reed beds over the weekend, to see the progress of our Reed Warblers and to marvel at just how lush and tall the beds had become. Many of the warbler nests now contained bright-eyed chicks, soon to fledge ahead of their journey south to Africa. Others contained newly laid eggs, with a handful of birds laying a second clutch in the same nest as their first but with others building anew. A couple of pairs had combined the two approaches, building their new nest on the top of the old to make a bizarre looking tower, woven between the reed stems.

One of the nests I checked on Saturday contained a young Cuckoo that we’d ringed earlier in the month. This Cuckoo was close to fledging, and sat on the rim of the nest, dwarfing the now flimsy construction that had once housed it. Alert, the chick turned to face me and opened its bill to reveal a vivid orange gape, a super signal to its foster parents to feed it with insect prey. I suspect that the brightness of the gape served another function, perhaps to warn off potential predators.

The one downside of working the reed beds this late in the season is the presence of a growing army of horse flies. They linger along the margins of the pools, most often where there is some damp and dappled shade; they soon discover any exposed flesh or, for that matter, any flesh protected only by a thin piece of material. My interest in insects means that I can still marvel at their jewel-coloured eyes, even when some of them manage to bite me. It has been a long season but a good one.

The be-witching hour

We are huddled around a moth trap on the southern margins of Thetford well after midnight, yet there is still the drone of traffic on the road to Bury. It has been a steady night so far, with a good mix of species in reasonable numbers, each drawn to the bright mercury vapour light of our traps. A low purr hints at the portable generator that provides us with the power needed for the traps, but it will only be when the fuel runs out that we become wholly aware of its intrusion into the still night. By that stage, dawn will not be far away and the passing traffic long ceased.

The strength of the light makes the darkness beyond all the more intense, our night vision gone. Moths buzz past our ears, occasionally blundering into us, pulled in by the light. You get a sense of the size of the moths as they approach, the more robust species trailing a whirr of heavy wings. We have with us some folk who are new to mothing and they are soon astounded by the colour and diversity of the moths on show. While the pink and ochre of an Elephant Hawkmoth creates a stir, it is the size of a Pine Hawkmoth that draws the most comment. This smart, but rather neutrally toned, species is a common catch in the Brecks at this time of the year, but this was not always the case.

The Pine Hawkmoth favours areas of open or mixed pine forest and is most strongly associated with the dry heaths and poor soils which have been devoted to timber production. It is the spread of these plantations that has really benefited the species. A century ago it would have been a rare vagrant here, but now Norfolk is well within its core range, a range that extends west into Dorset and north to Yorkshire. As its name suggests, the larvae of this impressive moth feed on pine trees, favouring the needles of Scots Pine. When small, the larvae lie along the length of a needle, relying on this slender camouflage for protection. They grow in a rather sluggish manner, becoming more conspicuous, before later descending to the ground where they overwinter as pupae under a carpet of moss or needles.

Adults are on the wing from May through into early August and are attracted to both light and to sweetly scented flowers. The females are initially reluctant to fly and remain on the trunks of trees where they await a male who will pair with them. The males, however, are more mobile and it is these that you tend to see in the traps.

Tuesday, 19 July 2011

A right royal colour

On hot sunny days it feels as if high summer reigns throughout the brecks. Areas of flowering grasses creep with the short buzzing calls of grasshoppers and the longer, high-pitched reels of bush-crickets. Stands of deep green bracken and a backdrop of brooding conifers create flat blocks of colour against which the yellow-greens of Dyer’s Rocket Reseda luteola and the soft purples of Vipers’ Bugloss Echium vulgare stand out as highlights.

I have always liked the bugloss, providing, as it does, a richness of colour at a time when other plants are coming to the end of their flowering season. I like the tenacious way in which it brings life from the dry, sandy Breckland soils. It is a plant that does well here, the features that made it unpopular with arable farmers now help it to eek out a living on this poor ground. Vipers’ Bugloss is a member of the borage family, with roughly hairy stems that make the plant prickly to the touch and a deep taproot that makes it difficult to uproot; no wonder the local farmers gave it the name ‘Devil’s Guts’. The plant was formerly a serious arable weed here, a reputation that it has carried with it to other countries, notably Australia and New Zealand, where it has been introduced. Although I have seen it referred to as ‘Paterson’s Curse’ by an Australian, this local name should really be applied to the closely related Purple Vipers’ Bugloss Echium plantagineum, a species introduced to Australia from the Mediterranean.

The name ‘Vipers’ Bugloss’ is something that has also attracted me to this plant. The ‘bugloss’ part of the name as its roots in the Greek ‘bous’ (an ox) and ‘glossa’ (a tongue), a reference to the shape and rough texture of the leaves. The ‘Vipers’ part of the name probably comes from the Roman physician and writer Diosconides who knew the plant (or more likely knew E. plantagineum) as ‘echis’ (viper or snake). Diosconides noted that the plant could be used as a treatment for a snake bite. This is a form of sympathetic medicine, where something that superficially resembles the cause of a problem can be used to treat it. The seeds of Vipers’ Bugloss resemble the heads of tiny snakes. In fact, the resemblance of the plant to a snake goes wider than this, as Richard Mabey so beautifully describes in Flora Britannica; ‘… sprays of flowers that spiral up the stem are half-coiled; the long red stamens protrude from the mouths of blue and purple flowers like tongues; the fruits resemble adders’ heads…’ To me, this description captures the essence of this plant and its place in my affections.

The most yellow of yellows

I have never been entirely comfortable in the Fens, something that I attribute to growing up within the comforting, verdant growth of the Surrey Weald, with its rich deciduous woodland and shortened horizons. There is just so much sky in the Fens, a great expanse of space that stretches on above; it is this that makes me feel exposed. The Fens are, however, part of my annual calendar, a place to visit in winter for the herds of swans and in the summer for Corn Buntings, Barn Owls and Yellow Wagtails.

It is a Yellow Wagtail that has caught my eye this morning; a sharp flight call alerting me to this cracking summer visitor. These arable lands, with their rich soils and dividing lodes and ditches, seem to suit this bird and here, just inland from the Lincolnshire coast, is one of their remaining strongholds. The Yellow Wagtail Motacilla flava has a massive breeding range, one that extends east across Europe and into Russia to reach Alaska beyond. Many different races occur across this huge breeding range, with ours the most striking of all; it is Motacilla flava flavissima, the most yellow of yellows.

Yellow Wagtails arrive from late March, with most appearing in April or May and with a few birds straggling in during the first week of June. I sometimes encounter them on passage, stopping over on bits of damp grassland. The breeding grounds tend to be in areas of wet grassland but arable landscapes (and crops) are also used. The drainage of favoured sites may be one reason for the decline in numbers that has been seen here over recent decades. This may not be the whole of the story, however, because there has also been a contraction in the breeding range, with the species disappearing from much of the southwest and north of Britain.

I see several Yellow Wagtails during the course of the day, with some carrying food into suitable nesting cover. These are wary birds, the adults feeding the young rapidly to avoid attracting unwanted attention to the nest. A calling pair, alarming with the characteristic sree sripp sripp a sure sign that there is a nest with young nearby. I sometimes get calls and emails from observers convinced they have seen a Yellow Wagtail in their garden. Many of these calls come in the winter, when the Yellow Wagtails will be on their wintering grounds in Africa. What these observers have seen will be a Grey Wagtail, a species that not only breeds across Norfolk but may also winter here. While Grey Wagtails do sport some yellow on their plumage, it does not compare to the resplendent tones of an adult Yellow Wagtail.