Late Summer Survey

Late Summer - or Early Autumn?   25th September 2018 was fine and clear after a cool night, no wind and dry although the last rain was only two days ago. Bank side trees still held plenty of fruits and the base of the bat flyway hedge revealed much activity. Hazels still carried most of their leaves but were getting bare on top, providing lookout perches for small birds. The river was fast-flowing after the recent rain, with crowds of 'Mayfly-type' midges hovering above the water in the still sunlit air.

Rosa canina rose-hips are prolific this year

Under an old oak - a cracking sound from overhead, then a thud as another acorn falls onto the dry ground, hitting leaves as it falls from a branch high in the canopy. Some of the old Field Maples have a more advanced leaf-fall, but each tree is different from the others of the same species, as the locations vary in this diverse landscape. This is true for the old oaks as well. A sudden breeze ruffles the leaves and the thudding of falling acorns increases - another bonanza autumn for small mammals and nut-eating birds. With more rain, the ground will soon be soft enough for them to start 'caching' supplies for the winter.

A month on from the previous record and robins have doubled in numbers, (26)  all of them singing loudly now, although there seemed to be fewer wrens (9) only one or two singing but those seen were clearly visible on low branches,  hedge bases or river banks. There are usually very few dunnocks visible but today 10 were seen in various locations, several singing but most were probably this year's juveniles, warming up, preening and chasing each other. They have done well with no summer floods to wash away nests this year. Given the right habitat they won't move far away.

Fast-moving blue tits  (about 40) were seen, mainly in mixed 'roaming flocks' together with other small birds following each other from tree-to-tree. Great tits (28) join in but there are always small groups which seem to inhabit the same choice location all year, mostly in sheltered places amongst large roots and branches. Coal tits too (2) mostly keep to their own groups.

Most migrant warblers have left the country for the winter but 2 blackcaps were seen and 3 chiffchaffs, all singing very short songs or making contact calls from the blackthorn thickets.

There were no signs of any migrant thrushes at this stage - far too early perhaps  - but bad weather in the north east will soon drive them over to us, when the wind direction is right. At present 12 blackbirds (thankfully now moulted into adult or new plumage) were seen, foraging on the ground or amongst the Blackthorn, together with 2 of our resident song thrushes. In the same thickets, two bullfinches were seen, probably a pair, the male calling very softly The only other finches seen today were house sparrows (about 50) in the best (warmest) locations in the sun on blackthorn thickets, on the river bank after bathing and amongst the warm brambles, some of which were still bearing Blackberries.

Hawthorn Berries awaiting the arrival of hungry migrant thrushes.

At this time of the year, with such rapid changes in weather, day length and food availability, birds cannot be expected to appear in the usual places. A good example today was the appearance of 2 goldcrests working their way along the bank in the company of blue tits and great tits amongst a rich variety of deciduous trees - a long way away from their usual conifers, whilst calls revealed 2 siskins then a group of 9 long-tailed tits following each other along the river willows which were rapidly losing their leaves.

At several different locations, a total of 6 nuthatches were calling and foraging in the old Oaks and Ash trees on the river banks, the time for establishing territories had started early, the young ones needing to find suitable nesting places by the time winter arrives. A great-spotted woodpecker was calling, flying into an old Ash.  Jays were as noisy as usual, (2) objecting to the presence of magpies (9) in the oaks whilst wood pigeons stared down on them, unmoved. More wood pigeons were seen foraging or flying across. (18 total) Four carrion crows were also present in the oaks, selecting topmost perches to call from and 3 collared doves, one calling softly. were in an Ash tree.

Looking down at the river, a moorhen was slowly paddling in a quiet meander when a kingfisher flashed past low over the water. Along the Arun, upstream where the water was flowing clear and fast, 2 grey wagtails were seen and heard, then two restless juveniles perching together on a thin branch across the river, flying out across the water onto the muddy flat bank then flying back to their branch again (total 4). They repeated this many times, snatching at low-flying insects. 

Starlings were resting today in their day roost, quietly whistling and singing in the sun. (about 20)

and 4 herring gulls were seen flyng across.

Masters of the sky today were the Common Buzzards, 6 in total. At first one was seen flying leisurely overhead, then 4 more were seen circling each other, calling and drifting with the wind, in a group. The last one appeared on the horizon, with a group of house martins foraging for flies lower down.

The house martins appeared as a group (at least 20 at any one time) then moved off and other groups moved in over the river course feeding on the aerial insects,  low over the oaks, hazels, willows, maples and thickets, then up higher then swooping down again. They were present here for the rest of the day,

probably making their way slowly south.

Butterflies still present were Speckled Woods and Large Whites with strong-flying dragonflies  -Brown Hawkers, a Migrant Hawker and inquisitive Southern Hawkers.

The conditions were so good that a bat survey was also done the same evening, during which an impressive Noctule bat (amongst many others) was detected and seen before the light went.
(see previous post below).

Bats and Birds

More on bats - but first the birds:

 Several days later and more fine weather, another look at bats.  Tuesday 25th September was another fine day. House Martins were circling in groups over the river, with varying but large numbers seen all morning, then more again towards evening when the air cooled.

The reason they were visiting the river was clear - abundant food was available in insect form, concentrated over the water.

The House Martins will be migrating soon and large numbers were already being seen on the south coast. Those seen today would soon be joining the migration as the hours of daylight diminish fast.

Dappled sun and shade on the warm river water and bank-side mud  brought out the insects

which could be seen low over the surface and high in the air over the river course.

House Martins quickly picked up the clouds of insects  over the tree canopies and were flying high and low following them. They won't go hungry on autumn migration this year, at least for the first few days.

What is good for house martins is also good for bats. Day-flying insects gave way to night-flying insects in large numbers. Covering the adjacent stretch of the river,  at dusk the sky was still bright in the west, as before, and bright enough to see bats flying rapidly, erratically across from one large oak to another, diving low over my head then up into the canopies, they can change direction much faster than birds - they are flying with their fingers - an exhausting process which means a continuous supply of food is needed. Common Pipistrelle and Soprano Pipistrelle bats were in the majority but Natterer's bats could be heard too. The bat detector was detecting numerous comings and goings in the dark of the trees. Echolocation was used as well as eyesight at first. It was clear that most bats were emerging from local tree cavity roosts and starting to forage immediately. Moving out from the tree margin however onto the short sterile grass of the recreation field at first no bats could be detected under the clear sky - but taking just a few steps closer to the overhanging trees bats were soon picked up. One or two were even audible flying across the corner, taking a short cut.

A large bat was seen to fly downwards over tree canopies from the evening sky, then very loud sounds on the bat detector  revealed that it was a Noctule, the largest bat encountered in this area.

After a slow start, bats seem to be doing well this year. They should survive in good numbers provided that their traditional roosts (both summer and winter) are protected - by conserving old trees in their natural state with holes and cracked branches and bark and natural understorey  vegetation with the local riverine ecology preserved. 

Bats need water as their unique physiology demands high levels of moisture intake from their insect food as well as the availability water in rivers, ponds or lakes.

Best for Bats

Tuesday 11th September was a fine day, with large clouds of small insects gathering over the river and river banks here and there, and larger insects crowding over bank-side vegetation where there were ripe fruits, with no wind to sweep them away. The evening sky was clear and bright and still light at 20.00 when the bat survey commenced after an impatient wait after the sunset at 19.19. Bats could still be seen by eye, silhouetted against the clear sky, for about 15 minutes but at 20.15 the sky was dark - plunging the riverside into darkness, time to use the bat detector.

Bright moonlight such as this, taken on 22nd July, can put bats off travelling and foraging - but on this night - 11th September, there was only a sliver of light, low over the horizon.

Starting at the base of the bat flyway hedge on the river bank, there were good numbers of Common Pipistrelle bats with some very obvious 'calls' (echolocation signals) from Soprano Pipistrelle bats interrupting them as their foraging flights crossed. Heading for a location where the river widens, some echolocation calls from Daubenton's bats were heard. Characteristically, initially the largest numbers of bats were in the vicinity of the very old riverbank oaks, with the earliest activity noted whilst it was still dusk, from bats emerging from their roosts in cracks  and holes in the old branches. These roosts may well have been used for hundreds of years where an oak could have been damaged by a storm and survived, as oaks do.

The timing has to be just right for recording the presence of bats using a bat detector, as most bats emerge from their roosts at dusk when they use their eyes to  forage, and we use ours to look up and see them darting amongst the tree branches. Later as it grows dark, they 'switch on' their echolocation ability which guides them, taking over from eyesight. Therefore we should not expect to 'hear' bats using a bat detector until it is dark. Bats make audible calls too, when communicating with other bats. 

Habitats that attract foraging  insects are best for bats - streams and rivers sheltered by vegetation with flowering and fruiting plants and sheltered woodland or wild fields and field margins. Bats, like birds and insects, are important pollinators too.