Keep an eye out for our smallest mouse

The winter months provide an ideal opportunity for collecting information on the distribution of Britain’s smallest species of rodent. Weighing just six grams when fully grown, the diminutive harvest mouse is rarely seen alive and many of the records that I receive, as county mammal recorder, relate to individuals taken by pet cats. The harvest mouse is the only British mouse to build a nest of woven grass leaves well above ground level and it is these nests that can be found by careful searching during the winter months. Two types of nest are built: a breeding nest (up to ten centimetres in diameter) and a smaller non-breeding one. Both are spherical in shape and composed of grass leaves, carefully woven together from living material by the female. There is no obvious entrance hole in a fresh nest and the female may enter and leave by forcing her way through the weave. After the female has abandoned the young, usually at around 15 days of age, they will continue to use the nest for several more days. During this time, obvious entrance holes may develop as the nest receives something of a battering from the young.

As the vegetation dies back in winter, harvest mice abandon the stalk zone in which they have spent the summer searching for insects and seeds, and move down to ground level where they use runs made by other small mammal species. Here they may build temporary non-breeding nests in the base of tussocks. A few years ago, I spent time studying small mammals in an area of wet meadow and it was only during the winter months that I tended to catch harvest mice in my live-traps, positioned at ground level. These russet-coloured mice are ideally suited to a life in the stalk zone and are equipped with a semi-prehensile tail, which they wrap around stalks to steady themselves as they move through the vegetation.

Because harvest mice need long vegetation, it is worth searching for their nests in areas of rough grassland, alongside the base of hedgerows or ditches and in reed beds. The well-constructed nests often last well into the winter and careful searching of clumps of cocksfoot grass can prove rewarding. Anne Brewster, who has been recording the presence of harvest mice around her village since 1976, has now found the species to be widespread locally. The species is probably more widespread within Norfolk than the records gathered to date would suggest. So, why not check out a few likely sites in your area and let me know if you find any abandoned nests. As county mammal recorder I am keen to improve our understanding of this often overlooked species.

A scatter of winter thrushes

It was wonderfully bright and crisp the other morning, as I explored the fields around Harling. Mobile tit flocks were much in evidence within the small patches of woodland, while great spotted woodpeckers could be heard drumming in the distance.  Near to the Dower House at West Harling I came across a mixed flock of birds that was feeding on an area of overwinter stubble. The flock was not overly large but was spread out over a reasonable area and, as I scanned across it with my binoculars, I was able to pick out a number of different species. Brightly coloured yellowhammers stood out against the stubble, foraging alongside less obvious greenfinches and the occasional chaffinch. Starlings shuffled about with a busy action, searching for food, among similarly sized redwings and larger fieldfares.

The fieldfare is one of my favourite birds, with a gait and pose similar to a mistle thrush but marked more distinctively. The bold, grey head and rump contrast with a rich chestnut brown back, dark wings and a black tail. These wary birds often stand with the neck and head held high, the wings drooped at their side and the tail held horizontally. They have a rapid, almost bounding gait and, when disturbed, they will take to the top of the nearest tree. The redwing is much smaller and more subtly marked than its larger relative. Slightly smaller than a song thrush, the redwing is darker in colour and has a distinctive white stripe above the eye (known as the supercilium). The chest has dark streaks, rather than spots, and the underwing is smudged rufous-orange.

Both species are winter visitors, arriving in autumn from breeding grounds that stretch across Fennoscandia and east into Russia. Arable fields containing permanent pasture and stubble are favoured and the birds feed on earthworms, snails and other invertebrates taken from the surface of the soil. In early winter, fruits and berries feature prominently in their diet but stocks are usually exhausted before the year’s end. Redwings, in particular, struggle during cold weather and will make nomadic movements to escape the worst of the cold. In some years, individuals will venture into gardens in search of food. Although more robust, Fieldfares may also visit gardens to feed on windfall apples.

This flock was one of few that I have seen this winter and there seem to be fewer around this year. It will only be a number of weeks until these wonderful birds begin to depart, though some may linger through into May and occasional birds have summered here in previous years. While their departure heralds the arrival of spring, it will be a shame to see them go.

Looking for wintering bugs

The other morning seemed suitably inviting to get out and about in search of overwintering bugs. Insects can seem a bit thin on the ground during the winter months but, if you know where to look, there are plenty to be found. I made my way to one of my favourite patches, armed with a stout stick, a pooter and a large white net. A pooter is a rather ingenious bit of kit that can best be described as a mini-hoover, with which you can suck up small insects into an observation pot. I started by working my way along the edge of a reedbed, stopping every few feet to position the net low down and to then tap the vegetation above the net with the stick. A fairly firm tap is usually sufficient to dislodge any insects and spiders that have chosen to overwinter in the vegetation. The white of the net enables you to spot those insects that are dislodged as they crawl around amid the bits of plant material that have also been dislodged. Within ten minutes or so I had several dozen individuals crawling around in the net: at least three different species of spider, two species of beetle, a caterpillar and various heteropteran bugs. Many of these were very small – one of the beetles was about the size of a pinhead – and most would need to be examined back at home under the binocular microscope before I would know what they were.


One of the spiders was familiar to me. Its elongated body and the way in which it held its legs – two pairs of legs fully extended forwards of the body and the other two pairs fully extended backwards – made it look like a fragment of grass stem. This was one of the two species of Tibellus spider known from the county. The pale straw colouration of these spiders helps them to perch inconspicuously on dried vegetation and ambush passing insects. Identification of this spider would definitely need a microscope, so subtle are the differences between the two species.


One species that would not need to be taken home for identification was a brownish-green bug, which had dropped into the net as I tapped a gorse bush. This was the aptly named gorse shieldbug, readily identifiable by its appearance and by the forward-pointing spine on its underside. As you might expect, it derives its name from an association with gorse and from the modified wings covering its back that give the appearance of a shield. Overwintering adults are brown in colour but come summer they turn a beautiful yellow-green. It had been a worthwhile visit, with a few more species to add to the list of those recorded from the site.

A late winter spectacle

As I have noted before, the long winter nights can cause problems for small birds and a number of species are known to roost communally to reduce heat loss. Such roosts can provide a spectacle for the winter birdwatcher, as tens, hundreds or even thousands of individuals congregate at favoured sites. Many readers will know of the huge starling roosts that may form at this time of the year but how many are aware of the roosts of pied wagtails or reed buntings that form each night throughout the winter months? Pied wagtails may gather to roost on large buildings, especially on some of the county’s larger supermarkets, and their loud ‘chis-ick’ calls fill the late afternoon air as individuals arrive from scattered feeding sites just before dusk. These congregations provide an ideal opportunity for teams of licensed bird ringers to catch and ring large numbers of birds, helping researchers to understand more about bird movements and survival.


Last Sunday afternoon, I was part of a team catching and ringing pied wagtails and reed buntings at a small roost in southwest Norfolk. The roost was in a reedbed, an ideal place to spend the night perched above open water and safe from predators, and the site has been used over a number of winters, although not always by the same species. A couple of winters ago, there were large numbers of starlings using the site. This winter there are very few starlings but fairly good numbers of wagtails and buntings. We arrived to set up our nets at two-o’clock and, once erected, all we had to do was wait for the arrival of the birds. Periodic checks of the nets during the intervening time revealed a number of wrens, all of which were local birds that had been caught at the site during previous summer sessions. Wrens often move into reedbeds during winter because this is one of the best places to find the invertebrates on which to feed.


As dusk approached, wagtails and buntings began to arrive. Parties of wagtails gathered together and wheeled about the sky calling, a spectacle that lasted for half an hour or so. The numbers of birds increased and then groups of individuals dropped down into the reeds, with some ending up in our nets. Quickly and efficiently our team removed birds from the nets and processed them, noting down details of wing length, weight and age (not an easy thing to discern in a pied wagtail) before letting them go so they could return to the roost. Other members of the team had, by this stage, packed away the nets and we were left listening to the occasional shuffles of birds moving to favoured positions in the reeds.

Pigeons feast on ivy berries

The end wall of my garden is hidden beneath a mass of ivy. Arising from a single trunk, whose girth far exceeds that of my thigh, the ivy has spread nearly thirty feet, bushing up and out along the wall. Over recent weeks the ivy has become the favoured dining location for the local woodpigeons, which have come to feast on the unripe berries. The antics of these birds are a delight to watch and I have been surprised by their agility. Individuals clamber about among the foliage, sometimes bracing themselves with half-open wings and stretching head down to reach more distant fruits. They rarely seem to over-balance but do, on occasion, appear less than dignified in their posture.


A hungry woodpigeon will fill its crop with a very large meal, eating up to 450 berries in a sitting, and will follow this with a long period of rest and digestion. Individuals that have had their fill loaf about in the tall trees beyond the end of the garden, sitting high and alert to occasional forays by the local sparrowhawk. It is during late winter that woodpigeons typically turn to ivy. The berries are nutritious and have an especially high fat content. Interestingly, when ripe, they are known to be moderately poisonous to mammals and at least some birds, if eaten in any quantity. It is not clear if the woodpigeon is immune to the toxins or whether it is able to deal with them by being particularly careful in how it treats the fruit once eaten. Perhaps the berries contain fewer toxins when unripe. The berries are an important stopgap, a food that is available at a time when other favoured foods have become scarce. Certainly, the pigeons seem to move onto ivy berries earlier in years when the autumn beechmast crop has been poor. 


Ivy is not the only winter food that woodpigeons have learnt to utilise. They have also taken to oil seed rape in a big way and the introduction of this crop has made a big difference to our woodpigeon population. Historically, under farming regimes with over-winter stubbles followed by the spring sowing of cereals, the lack of suitable food between January and March was known to be the controlling factor behind woodpigeon population change. Many woodpigeons would starve during this period and the population would be kept in check. With the introduction of this new crop, the brake halting population growth has been removed allowing our woodpigeon population to expand in the manner that it has over the last ten years. This may be one of the reasons why so many woodpigeons seem to descend on my garden at this time of the year.

Are Norfolk's deer becoming a problem?

There has been quite a bit of discussion over recent months about the numbers of deer within the county. This has been part of a wider debate about deer numbers nationally and concerns have been expressed about the impact that they might be having on forestry and farming interests, other wildlife (by damaging woodland vegetation) and through collisions with motor vehicles. Just last week, there was an article on the subject in one of our local newspapers. The debate is an interesting one, particularly so for me in my role as County Mammal Recorder, and it raises a number of important issues centred around the interaction between humans and the other wildlife with which we share the countryside. 


Introduced species, such as muntjac and Chinese water deer, seem to be doing very well within the county and both species have increased in numbers and range over the last few years. Drive along any of the roads through Thetford Forest on a summer evening and you will see several dozen muntjac grazing on the verge during the course of your journey. These small, dog-sized, deer are surprisingly solid and any collision with a motorcar is likely to be damaging to both parties.


Research has demonstrated that at high densities, deer populations damage deciduous woodland by preventing natural regeneration and by removing much of the ground flora. This, in turn, reduces opportunities for other wildlife and is thought to be one of the reasons for the declines seen in a number of woodland bird species. Experiments using deer fences to exclude deer from small blocks within woodland show just how pronounced the impact of deer grazing can be. 


There may be good ecological and commercial reasons for the numbers of deer to be controlled and control through shooting has been an important component of forest management within the county for many decades. As with any control programme, it is important to know how many individuals there are in an area in order that a suitable level of control can be established. In the case of deer this can be something of a problem. Deer populations are not easy to monitor, in part because of their secretive nature, but also because populations may range over large areas. Traditional methods of monitoring mammals, such as recording field signs like tracks and droppings, are not always readily applicable to deer and require a high degree of skill on the part of the observer. Having said this, efforts are being made to build up a more complete picture of the number of deer in our region and various organisations are working together, through the Deer Initiative, to improve our understanding of these wonderful animals.

Worrying decline of much-loved bird

The largest and most majestic of our breeding finches, the hawfinch, is a now an increasingly rare delight for the Norfolk birdwatcher. With its cinnamon and chestnut plumage, black bib and extremely stout beak, this wonderful bird is one of the real gems of the bird world. Unfortunately, its elusive and secretive nature, coupled with an alarming decline in breeding numbers, make this a difficult bird to see, especially during the breeding season. It is during the winter then, that it is well worth visiting one of the handful of sites which support small wintering flocks. Within Norfolk, Barnham Cross Common and Lynford Arboretum, both in the west of the county, are the most reliable sites. However, even here the birds can be difficult to see. 


During the winter months, the hawfinch feeds on the fruits and seeds of various trees, favouring those of hornbeam, field maple and cherry. The bird uses its stout bill and very well developed facial muscles to crush open cherry stones. The stone is held within the bill, balanced on four horny pads attached to the inside of the upper and lower mandibles, and the bird then applies a crushing pressure reported to be more than 1,000 times greater than its own body weight! This ability is reflected in the bird’s Latin name of ‘Coccothraustes’, which derives from two Greek words meaning ‘a kernal’ and ‘I break into pieces’. The power of the bill, coupled with an aggressive nature, is probably the reason behind the rather peculiar courtship display of this species. The display is highly ritualised and involves a large number of submissive gestures and a very cautious approach on the part of the male.


The Hawfinch has a very patchy distribution in Britain and the most important populations are now located outside of Norfolk. These populations have declined, possibly because of changes in the quality of favoured woodland habitats, increased competition for food and nest predation by introduced grey squirrels. During the 1970s and early 1980s large flocks would be fairly commonplace in winter but flocks in excess of 10 birds are now most unusual. This pattern can be seen in Norfolk. In the winter of 1974/75 a flock of some 183 birds was present at East Wretham but by 1986 very few birds were using the site. Numbers at the Lynford and Barnham Cross Common sites are also far smaller than they once were – both in single figures. For how much longer will we hang onto these wonderful birds? However, there is one piece of encouraging news. Following a tree planting campaign, numbers have been increasing on the Dutch polders. Perhaps the hawfinch may benefit from similar schemes here in East Anglia.