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Loch Lomond and The Trossachs National Park

Weekly Nature Watch

Weekly Nature Watch 28 June 2019

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Although we've only just passed Midsummer' Eve, already there is a slight falling away in the volume of bird song, a gradual dampening down. 

For many, the frantic nature of their summer breeding season is coming to an end with new families now up and flying.  Many adult birds will, I'm sure, be relieved that they can at last see light at the end of this particular tunnel.  Once we reach the end of June and July begins to dawn, the frenetic nature of their lives in their drive to produce the next generation calms.  During these next few days and months, there will be a chance for them to draw a breath and prepare themselves for the next phase in their lives, at which time many will enter their main moult of the year.

The process of replacing plumage is an on-going process but now as we enter the second part of summer, a major moult and a renewal of feathers is undertaken by most birds.  Some birds become flightless during this process, whilst others, as they cast their flight feathers, are to some degree debilitated and are thus more vulnerable to attack by predators.  Hence singing, by and large, is off the agenda.  Birds that are handicapped by this major loss of plumage certainly don't want to advertise their presence and thus fall largely silent.  I don't know how many times I have heard visitors to our landscape during July and August, commenting that there seems to be a lack of birds.  However, the birds are there, albeit noticeably in reduced numbers these days, but we don't hear too many of them once they begin to shed their feathers.

There was, commonly, one notable exception to this rule in the colourful shape of yellowhammers.  Being prolific breeders, often nurturing a third brood during those late summer months, they were often the lone songsters during July and into August, their 'little bit of bread but no cheese' ditty echoing from many of our otherwise relatively silent hedgerows.  However, as I recently reported, their numbers are plummeting and I haven't heard them in this locality for at least a couple of years.  Instead of removing hedges, better management of these vital wildlife corridors could help to restore the balance.  Indeed, it can be argued that we need a landscape, which is less stringently manicured and managed and where some weeds are allowed to grow, before this sad decline in yellowhammers and other farmland birds is likely to be halted and reversed.

However, there are other birds which are still deeply embroiled in the business of nurturing young.  The ospreys will continue to feed their new generation at least until late July or early August and of course so too will the swallows and martins.  There has been a decrease in the number of both these wonderfully athletic summer migrants this year and especially so in the case of house martins.  I understand that the weather over the Continent was particularly stormy at the time these birds were heading north on their spring migration.  Thus, some may have perished whereas others might have been seriously delayed during their northerly passage.  My own observations suggest that many of the martins that are here were unusually late in arriving.

House martins, especially, do try to produce three broods of young during their summer sojourn with us.  However, I suspect that many of them this year will have to be satisfied with just two broods, as a late arrival reduces the time they have to raise and nurture multiple broods. It must be assumed that their vulnerability during migration is high if they need to produce three broods every year in order to maintain their numbers.  Swallows too, journeying some six thousand miles all the way from Soutn Africa, must also suffer losses and indeed we do know that the crossing of the massive Sahara Desert, accounts for a fair number of them.  The other negative factor may be connected with the serious downturn in insect populations recorded both here and across Europe.  Both swallows and martins depend entirely on insects and so this shortage is bound to affect them.

The speed at which different birds moult is very much related to how and where they spend their winter.  In other words, those that are migratory must moult at a faster rate than those that are sedentary because they have to be well prepared for their epic journeys.  For instance, blackcaps take around thirty-five days to complete their moult, although increasingly these wee warblers seem to be opting to spend winter in the southern reaches of Britain. Will this mean I wonder, that gradually blackcaps will take longer to moult than is the case now?  Short distance migrants like redpolls for example, take longer, something like fifty days to complete their moult.  Compared to this relatively rapid moult, resident songbirds such as thrushes and blackbirds, destined to remain here for the winter, do not need to hasten the process.  Having no migratory deadline to meet, they may take 80-90 days to fully complete their moult.

In contrast, some like garden warblers, swallows and perhaps surprisingly, cuckoos, will not moult until they have completed their migration to their wintering grounds in Africa and indeed the process can be prolonged in some cases, lasting most of the winter.  Unusually, willow warblers moult twice a year, possibly because their lifestyle and breeding habits mean they spend a great deal of time making their way through thick vegetation, which takes a toll on their feathers.

However, it is the water-based birds that really take their time moulting.  Ducks and grebes for instance, shed all their flight feather at once and so actually become totally incapable of flight for several weeks.  Therefore, you will see them skulking about in reed-beds and the like during this time when they are obviously more vulnerable.  And of course. many of them also have the option of diving to evade attack.  Many years ago I certainly remember watching a couple of goldeneye which were being pursued close to the loch by a sparrowhawk, descend quickly to the water's surface and immediately dive leaving their pursuer utterly baffled by their sudden disappearance.

Male ducks - the drakes - also go into an eclipse moult at this time, emerging in plumage which is as dull as that of the females, making them more inconspicuous.  Indeed it is easy to get the feeling that all the drakes have disappeared after midsummer as they don't regain their full colours until October.  Our commonest duck, the mallard, very clearly demonstrates the difference between the duck and drake.  The drake is attractively colourful with its bottle-green head, white collare and purplish brown breast, its back greying brown, whereas the duck is very much a plain Jane, with mottled brown plumage.  Her one concession to colour is her blue wing flashes.

The drake needs to be colourful to sucessfully compete with other drakes and attract a mate.  In other words, he is the 'waddling wonder-kid' but the duck, nesting as she does on the ground, needs therefore to be well camouflaged and discreet.  However, as in almost all species, it is that 'plain Jane' of a duck, who ultimately makes the choice of mate.  Therefore, when breeding time comes along, he has to be at his best, but when he moults he too needs to be camouflaged and discreet.

So its time for new sets of clothes, a matter of urgency for those destined to launch themselves on epic migratory journeys but perhaps a matter of personal pride for year-long residents like those familiar mallards!

Any natural place contains an infinite reservoir of information, and therefore the potential for inexhaustible new discoveries.

Richard Louv, Last Child in the Woods