Harvest mouse remains overlooked

The other day a friend was telling me about a recent encounter with some harvest mice, his first sighting of these overlooked mammals in thirty-odd years of watching wildlife. Two of these tiny creatures were clinging to some reeds in an area that had been inundated with floodwater and he was struck by their small size and by the delicate way in which they used their tails to secure their hold on the reeds.

The harvest mouse is a mammal that I know well, having once kept and successfully bred them in captivity. They are amazing creatures, far more delicate than their larger relatives (like wood mouse, which I have also kept in captivity) and with a lot of charisma. It is difficult to know how common they are across the county, their small size and arboreal habits make them difficult to trap using conventional live traps, and I suspect that they are easily overlooked. Most records will either come from cat owners, whose pet has delivered an unfortunate harvest mouse to its owner, or from those who encounter the cricket ball-sized nest in a field margin or reedbed setting. Other records come from the pellets cast by hunting owls.

At this time of the year harvest mice may still be giving birth, the first births beginning in late June and the last extending into October or beyond. Cold wet weather at this time of the year can be a particular problem. The nest into which the young are born is up to 10cm across and woven into the vegetation. The young mice will use the nest for 2-3 weeks, the female abandoning them at 16 days if she is pregnant with her next litter, and the nest then becomes increasingly battered as the youngsters explore their growing world and gain independence.

I used to find harvest mice would enter my live traps, set for field voles on a wet meadow, from November through into March, suggesting that at this time of the year they spent more time on the ground. It was always a thrill to see the russet-orange of a harvest mouse drop into the polythene bag into which I emptied the contents of any trap that had been triggered. Once released on a stem their agility could be appreciated and, if I sat very still, they would sometimes sit and groom, balanced by tail and a single foot alongside the vertical tube of plant stem. It was these encounters that probably made the harvest mouse my favourite mammal, topping even the dormice that I had studied in Sussex several decades ago. It’s been a while since I saw a harvest mouse so maybe I should go looking for one.

Our engaging little owl

Despite its small size the little owl boasts a big personality, much of it expressed through the piercing yellow eyes with their black ‘eyeliner’ rims. This owl can be seen across the county, though it is rather thinly distributed compared to its status in certain other counties. To see one on a walk or while out birdwatching is, therefore, a real treat. Sometimes the bird may be flushed from some unseen perch, flying away with a deeply undulating flight. On other occasions the owl will remain perched, watching intently and occasionally bobbing its head in comedic fashion. These pronounced head movements are a feature of owls more widely. Known as motion parallax, the movements artificially change to the location of an object being viewed on the owl’s retina, something that increases the owl’s ability to estimate the location, distance and motion of an object.

The presence of the little owl in Norfolk owes its origins to introductions that took place during the 1800s, the owl successfully established in Northamptonshire and, later, other counties. A few Norfolk records pre-date these introductions and probably refer to genuine vagrants, arriving on the coast after a long sea crossing. In 1862, for example, one was found on a fishing smack 10 miles off Yarmouth. Birds first bred here in the early 1900s and by the 1930s the species was commonly noted breeding across the county.

Little owls seem to do well on the large Norfolk shooting estates. Not long after the little owl became established here concerns were expressed that it might take gamebirds and their chicks. However, a detailed study by Alice Hibbert-Ware at the BTO revealed the diet to be dominated by invertebrates and small mammals, suggesting that the owl was a beneficial addition to our avifauna. Nevertheless, on some shooting estates the little owl remained the unfortunate victim of traps set for other birds of prey.

Although it is not unusual to see little owls during the day, they are essentially crepuscular in nature. Activity peaks in the hours immediately after dusk and again just before dawn, matching the period when favoured prey are most active. Hunting from a perch is a favourite means of locating large beetles, small mammals and earthworms, the owl dropping onto its prey with a short flight. Sometimes the owl will hunt while on the ground and may run short distances to grab at an unsuspecting worm or other delicacy. They can be very adaptable however. A pair living on an offshore island specialised in taking storm petrels from their burrows, much to the consternation of the warden. Even he was struck by their personality, solving the problem by relocating the birds to the mainland.

Help to find out about birds and berries

It is at this time of the year that I start to see migrant thrushes, newly arrived and busy feeding on the abundance of berries and other fruits that adorn the county’s hedgerows. Berries provide a ready meal for blackbirds, song thrushes and redwings – the latter not arriving in numbers until later into the year – and in return the birds disperse the plant’s seeds into new areas.

Follow the progress of the berries through the winter and you’ll discover that some seem to last longer than others, perhaps because they ripen later or because they are less favoured and are only used when other fruits have been stripped. In some cases, a berry-bearing shrub may be defended by a mistle thrush or fieldfare seeking to secure a food reserve for future use. Whatever the reason, the seasonality of berry availability is likely to be important, influencing where birds feed and when. Taken to an extreme in a species like waxwing, individual birds may range of vast distances to find an area where berries are plentiful.

The interaction between birds and berries is something that has attracted the interest of the BTO, who are running a study this winter to look at how thrushes make use of the berries to be found within our gardens. Some of these garden berries may be native in origin, others introduced and some will be domesticated varieties of wild species. Since berry colour can provide an honest signal to birds of the nutritional value of a particular berry, it is possible that some of the varieties we have selectively bred to produce a particular berry colour (e.g. pink or white) may now be unattractive to the birds. Birds may also preferentially select native fruits over non-native ones, or vice versa – the selection influenced by availability and/or the timing of fruit production.

In order to examine these questions the BTO has asked for our help. By making simple observations of berry availability and of berry use, we can provide the information needed to better understand the relationships that exists between plants and the birds that disperse their seeds. If, for example, non-native plants are favoured over native ones, then this might give them an increased opportunity to become established more widely across the countryside. Could we expect to see Cotoneaster and Pyracantha becoming established in our woodlands and hedgerows? The work should also provide better guidance as to which shrubs to plant for the benefit of our wintering thrushes and other berry-eating birds.

To find out more and to receive a free guide to berries, write to Birds and Garden Berries, BTO, The Nunnery, Thetford, IP24 2PU or email gbw@bto.org.

In search of thunder

The chances are that you will be familiar with ‘thunderflies’, those tiny dark insects that are most evident during the muggy warmth of hot, late summer days. Look around the framed pictures in your house and you might even spot the body of one that has insinuated itself behind the glass of a treasured picture. You might have swallowed more than one if a keen cyclist or jogger, or had one get caught in your eye while out on a walk. For their size, these diminutive insects can be disproportionately annoying! But how much do you really know about them? Did you know, for example, that they belong to an order of insects known as Thysanoptera (which means ‘fringed wings’) or that they are commonly called thrips? If you did, then were you aware that the singular of ‘thrips’ is ‘thrips’ and that there is no such thing as a ‘thrip’?

Size matters when it comes to our interest in insects; size and economic value. We humans rarely take much of an interest in something as small and seemingly insignificant as thrips, unless it happens to impact on our way of life. Thrips, and there are somewhere in the order of 150 species known from Britain, include species that are pests of agricultural products, from glasshouse crops to cereals, peas and even onions. Some feed on plant leaves, their populations sometimes reaching levels where severe damage is caused to the plant, which may become stunted and turn yellow. The damage occurs because the thrips suck out the liquid contents of the leaf cells, occasionally inadvertently introducing a damaging virus to the plant in the process. Others feed on flowers, extracting the contents of pollen grains, or feed on fungi, often out of view beneath rotting bark.

Those most commonly encountered in the field tend to be the ones that feed on flowers. The dark adults often stand out against the brightly-coloured background of the flower. Earlier in the year you may have noticed black thrips on ox-eye daisy. These are likely to have been feeding, mating or egg-laying, the eggs deposited into the florets. At this time of the year, look on heather or bell heather for other species.

While you should be able to be able to recognise a thrips for what it is, taking the identification further (to family or species level) is particularly challenging. A high-powered microscope is essential, together with an identification key and hours of patience. It is perhaps better then to appreciate them in a generic sort of way, as tiny insects whose countless numbers are testament to a successful way of life. You might even come to admire the success of such a tiny creature.

Toads much in evidence

Even though I have had little time to spend working in the garden this summer, I seem to have seen the resident toads more frequently than in previous years. Last thing at night I have often come across one on the gravel path that snakes its way up the garden. Sometimes one can be seen on the patio, where it attracts the passing interest of the dogs and, occasionally, one appears outside the back door causing my heart to skip a beat as I almost tread on its vulnerable form.

The toads have never bred in the garden, the pond perhaps too small and dominated by other amphibians, whose tadpoles would out-compete those of a toad, but they have been ever-present since we moved in here more than a decade ago. There are larger ponds in nearby gardens and these may be the source of the smaller toads that are seen from time to time in the garden, for it is the larger individuals that are most often encountered. The largest of these may well be females, the bigger of the two sexes. The two sexes are fairly similar in appearance, though the warts are less prominent on the female and the toes of the front legs more delicate. Mature males develop characteristic pads on their inner toes during the breeding season, these being used to grip the female.

Common toads are terrestrial in habits for most of the year and seem well adapted to life on land. The garden almost certainly holds sufficient prey to support several toads and I suspect that our resident population is, judging by the sizes encountered, a mixture of immature and mature individuals – maturity is reached three or more years of age in females and two or more in the males. One particular individual must hide up near the shed, for it is often seen here during early evening. Although the background colour of her skin (I think of this particular toad as a female) changes with the light, from dull olive green to a warmer green-brown, she has a characteristically-shaped black splodge behind her right eye. The most colourful feature is the eye, a black horizontal pupil bordered by a yellow-orange iris, which darkens where it meets the horizontal to create a three-dimensional effect and the illusion that the top part of the iris is jutting out like a baseball cap.

Seen close-up, best accomplished by lying prone on the ground next to the toad, the delicate pattern of the warts can also be seen, as can the paratoid glands, positioned behind the eyes. It is from these that the toad can release its foul-tasting toxin. Little wonder the dogs leave them well alone.

Tottering along the water's edge

A scatter of showers has been passing through all morning, some skirting the surrounding hills but others rolling overhead to deliver waves of heavy, slanting rain. With each approaching shower the wind lifts, white tufts are created on the now rippling water and wading birds are buffeted as they halt their southward journeys to feed from the gleaming mud. I am in Rutland and this particular lagoon provides one of the few opportunities in the county for passing waders to stopover and feed. There’s also a good chance of osprey and an even better chance of hobby.

Tucked, as I am, into the corner of a distant hide I have only occasional company. There is none of the blokey banter than can plague birdwatching trips to more popular sites, with the endless ramblings of those keen to tell you what they have seen at other sites and in other countries. I can enjoy the birds alone, selfishly undisturbed. Out front, hirundines rake the air, while terns drop to pluck food from the water’s surface and dunlin and snipe haunt the margins. Two Egyptian geese look wildly out of place, perched on one of the osprey nest platforms, but perhaps this scene is closer to that of their Africa homeland than the ornamental lakes and stately home backdrops of their adopted Norfolk stronghold.

A brief, ringing call alerts me to the presence of a greenshank. Scanning with my binoculars I catch sight of the bird as it flies in to land just 20 metres distant, the spear-tip of white that extends from the rump up the back, bright against the darkening sky. The bird moves across the mud, tottering on exaggerated legs and with head facing into the wind. Every now and then it tacks left or right, head still down and forward, buffeted but never unbalanced.

The greenshank is a passage visitor to Rutland, perhaps from breeding grounds in northern Britain or, more likely, from further afield. This is a species of lonely uplands and forested marshes, a bird that moves south from late summer onwards, wintering in southern Britain, Continental Europe and on into Africa. Most of those passing through eastern England will have begun their journey in Scandinavia and be heading for West Africa. The earliest of the birds to be on the move will have been underway in late July but pasage will continue into November, making this a protracted period of autumn migration. I am sure that I will catch up with more of these elegant birds as the year tips towards it end but for now this individual has my full attention. It is a wonderful bird, understated and quietly elegant.