Archive for the ‘Harvest from the environment’ Category

Feeding the Song Birds

February 28, 2014

Things that healthy birds do not need – beware what is put on the bird table!

The advice being passed down to the bird loving public, often takes no account of the biology of the birds!

Birds are like humans, they will flock to eat stuff that is really bad for them.  Research work over the past 50 years on bird rearing agrees with me, and demonstrates that a diet of fat results in increased deposits of internal fat especially around the gonads.  This problem is made worse by the fact that the body uses fat as a storage organ, it is in the fat that any chemical pesticides that don’t kill the birds outright, will end up.  This reduces fertility in all species, and so will lead to a further decline in song bird populations.

If you think about it, the only birds that kill fat animals or birds, or that you see on ‘road kill’ are the raptors and corvids.  These are not normally the birds that you want to attract to your bird table as they have a habit of killing the smaller song birds.  Likewise, our birds do not naturally crack open nuts for the very simple reason that the only nuts native to this country are hazelnuts and pine nuts.  The former are so hard that only squirrels and mice can get into them; whereas the latter are eaten by the Crossbills – whose beaks are specially adapted to winkling the pine nuts out of the pine cones.  The little Goldcrests and Firecrests that also breed and shelter in coniferous forest, are feeding on aphids, springtails, small flies, grubs, and pollen, but not the nuts that they could never reach!

For a healthy song bird population, try to give your garden birds more of the foods that grow naturally in this country.  Remember too that very few, if any, birds are complete vegetarians.  They do eat small grains, seeds and berries in the autumn, but for most of the year, they feed on whatever insects, worms and grubs that they can find, supplemented by a peck or two of annual herbs e.g. dandelion leaves.  So in the winter, supplement their natural food with small grains etc; but better still, do all you can to promote small insects, bugs, spiders, worms and fresh leaf growth e.g. of dandelions etc.  These are all really good for the birds in this country, and will not cause them to lay down unnatural fat around their internal organs.

The other thing that is needed by over-wintering birds is natural cover.  Dense thickets of brambles are excellent, providing both cover and insects; while standing under our line of Lawson cypress trees at my own home on a winter’s evening, revealed the song birds’ favourite spot.  They would congregate up in the branches under the thick evergreen cover of the conifers and chirp away, warm and dry.  Yesterday, visiting a friend in Taunton, I was horrified to see that the Somerset CC had been busy removing a bramble thicket along an area that they had designated as wildlife habitat beside the River Tone – so much for their knowledge of wildlife.  Plus of course, they have removed the possibility of the thousands of humans in the area being able to pick blackberries that are not wrapped in plastic containers, and to actually make their own blackberry and apple jam.  The wild eaters of the blackberries are mostly little field mice, while the birds feast on the spiders and flies that are also attracted to the fruit!


Ivy – Hell Bent or Heaven Sent

August 24, 2011

Written as a blog in response to a letter by Lt Col Paul French (Rtd.) in the Daily Telegraph of Monday 28th March 2011.

Most of us who love trees for their timber and role in the landscape, regard Ivy as a foe.  The wild variety in the UK is named Hedera helix, though from its growth pattern it would be more aptly named Hedera rete i.e. Ivy net.  However, there are three views of  ivy: that of the tree; that of the birds, bats, insects and fungi that live in and on it; and that of humans and the browsing animals.  In past centuries: before the reign of plastic, huge human populations and high wages; all trees, farmland, woodland and forestry, were cared for by the humans who worked the land.  Ivy was left to grow only on those trees that were already misshapen, or of a species whose timber was not considered to be useful.  Even then Ivy was controlled by deer and cattle that were permitted to seek the shelter of the woods in winter, where they kept down the undergrowth.  Their grazing kept the glades open so that Wild Garlic and Bluebells could get enough sunshine to grow and flower ahead of the herbs and thin grasses in the spring.

Viewed from the tree’s perspective it is definitely a devil.
The creeping stems of Ivy are coated on one side with tiny suction rootlets that enable it to climb up the trunk and cling to the bark of  the tree.  Generally it does not attack until a young sapling has become too inflexible to fling off the unwanted guest as it bends in
the wind.  Then, when after several years the trunk has lost its whippy characteristic, and is suitably firm and steady, the Ivy colonizes.  Unless it is broken off by humans or browsers, ivy grows steadily upwards branching as it goes, until it reaches a level at
which the branches are still whippy enough to shake off the tendrils for the time being.

Like all evergreen species, although it does not shed its leaves seasonally, they gradually age and drop off.  They then cause even more trouble: by lodging in the angles of the boughs, and with other leaves they rot down leaving a black leaf mould that in turn plays host to epiphytes – mosses, nettles and ferns.  The bark beneath then starts to rot, thus weakening the branch, and allowing the rot to penetrate the heart wood of the tree.  The living Ivy leaves also cause problems by sheltering the bark from the rain, and the ‘rootlets’ absorb any water running down the surface of the bark.  This leaves the bark dry, brittle, and cracked so that it is easily penetrated by insects and fungal spores.  These often carry diseases, both bacterial and viral, which are, in turn, transported into the sap that runs in the living layers just beneath the bark.  In this way pathogens can be carried up into the leaves of the canopy or down into the root system.

Worse still Ivy keeps its leaves throughout the winter, thus adding weight to the branches and extra surface area to catch the winds.

The ivy here has climbed nearly to the top of the birch tree and the weight of its leaves is slowly pulling the tree over.

Slow felling of a Birch by Ivy

  This at a time of year when our deciduous trees have shut down and shed their leaves, thus protecting themselves not only from the cold, but also from damage by winter storms.  In a young sapling the situation is not so serious, as it is often both strong and flexible enough to carry the extra leaf area without cracking; especially so since the ivy is young too and equally flexible, but the story is very different for the older tree.  Veteran trees often have ivy stems of over 6cms diameter half buried in their bark; and these vast old creepers add substantially to the weight to be carried by the branches, made even more fragile by the lack of moving sap during the winter months.

The result is very visible damage.  Some unlucky trees are completely thrown and partially up-rooted; some escape; but most veteran trees suffer the breaking of large boughs and even smaller branches in the crown of the tree.  These breaks leave scars that not only spoil the visual shape of the tree, but may also unbalance the tree, making it more susceptible to wind damage in the future; not to mention the increased risk of disease entering the broken timber via rain and spores.  All this damage hastens the slow demise of the tree.  However . . . .

Viewed from the denizens of the tree the story is very different; for everything, that the tree could be expected to regard as negative, is positive to them.  In fact the more the tree is damaged, the better the better it becomes for them.  Though as it disintegrates, they will all have to move on, starting with the birds and insects and ending with the decomposers growing on the rotting wood.  This is the way that it has always been.

In regions where there are no convenient conifers, ivy-laden trees provide some of the only safe shelter for small birds throughout the winter months; besides providing an every ready larder of spiders, flies, beetles, millipedes and mites throughout the year.  Bats too, can be found sheltering under the ivy during the summer; though it is possible that they are really looking for suitable warm sheltered holes to use for winter hibernation.  As for the rest: the birds’ living larder and the fungal spores; the ivy provides warmth, shelter and nice little cracks in the bark with good access to sap – an ideal growth medium for the fungi and any pathogenic bacteria and viruses spread by the insects.  Finally . . . .

Viewed from the requirements of humans and browsers the story becomes split.

On the ‘Up side’, the latter seem to regard Ivy as we would a tasty herb.  However, it is probable that their actions are related to self medication, as Ivy is a known anthelmintic that has been used as such in the past.  Animals may not be able to read books, yet many seem to either know or learn that certain ‘herbs’ are beneficial when eaten in small quantities.  So long as the plant is bitter they don’t exceed the safe dose; it is only when the plant is sweet, either alive or when dead e.g. Ragwort, that they over eat and poison themselves.

Humans too have used Ivy leaves as a medicine for thousands of years; though now-a-days its use is limited to external applications because of unpleasant side effects and its ability to destroy red blood cells if imbibed in excess.   However, externally the leaves still provide a useful herbal poultice for leg ulcers, enlarged glands, painful joints and other pains that can be reached from the outside!

This oak is completely encased in ivy, only the dead branches remain sticking out above the luxuriant growth.

Ivy engulfs its prey - a veteran oak dies

On the ‘Down side’ humans have always grown trees, not only because of their beauty, but also because of their many uses: for food and the energy to cook it; for medicines; for timber with which to make houses, tools, and all the plethora of things that are necessary for a good quality of life; and for ashes to make lye for soap making.  So overall, anything that affects the health of trees qualifies as a devil rather than an angel from the point of view of humans.

But that is not the full story and Ivy too has its uses.  Perhaps the solution is: to remove ivy* from all straight trunked trees and those that are suitable for structural or ornamental timber; then remove it from 25 – 50 percent of the remaining trees.  25% of trees with ivy is quite sufficient in our heavily treed areas e.g. Dorset and Devon; but in areas where trees are more scarce e.g. Northumberland then 50% of the remaining trees with ivy might be acceptable.  Let common sense prevail, and preferably prevent  our non-governmental public bodies and allied groups from removing all our conifers on the grounds that they are not native, or that their English names fail to suggest that they should live south of the border e.g. Scots Pine (Pinus sylvestris) which is prevalent right across Europe from North to South.  To my certain knowledge trees are totally unaware of geographical boundaries – unless they coincide with environmental attributes such as climate, aspect, rainfall and altitude!  However, the conifers do provide very good protection from inclement weather for wildlife and particularly for small birds, many of whom crowded into our group of Lawson Cypresses at dusk on a winters evening, and provided a chirrupy sort of concert for any who cared to stand under and listen!

*Ivy removal is simple.  Pull the small stems off young trees using fingers, before they become established.  For older, thick stems of ivy use a saw, billhook or chopper, to cut and remove a 5cm/2 inch segment from the base of the trunk.  Try to avoid damaging the bark where possible; but a little damage to a small piece of bark is preferable to much the much greater damage caused by the ivy.

Thoughts on Hugh’s Fish Fight

February 1, 2011

I have just signed Hugh Fearnley-Whittingstall’s petition to stop dead by-catch being thrown back into the sea. But pausing to think about this part of the catch, I realize that there are actually many problems associated with removing it from the marine environment.

Of course the real answer is not to take by-catch; nor to over fill the nets when bringing them to the surface. Having been out on a university research trawler in the 1990s, I am fully aware that the sonar scans and computer information from other boats  mean that the species of fish in a shoal, and its precise size, is known as the trawler approaches the region; and thus well in advance of the net being released in the first place.  Bottom trawls are a very different ‘kettle of fish’.

The number of fish that will die depends on several factors, amongst which, the way that they control buoyancy is probably the most important (see “Buoyancy Matters” end of this note).  Fish that cannot, or are slow to dive are the ones that become prey to the wake hugging gulls.  Those that have lost the ability to control their buoyancy, gradually sink through the water column, becoming dinner for scavengers on their journey to the bottom.  Other fish, krill, copepods and indeed bacteria and algae would normally expect to benefit from the extra nutrients that are thus released into the marine ecosystem – after all most marine organisms live and die in the sea.  If the by-catch came from the sea floor, then providing that they are still alive and don’t get caught by a gull, they don’t usually have swim bladders and will slowly drift down, be reunited with their food source and will survive the experience; though even for them the sudden pressure change may be a problem.  But normally, the ecosystem in which trawled fish live, is sustained by a rich mixed food source that contains some photosynthetic organisms and so moves up and down within the surface layers, stimulated by light and dark at the surface.  For these pelagic fish, it is the speed with which the trawl comes up to the surface and is hauled aboard that is the problem.  If it happened slowly enough most swimbladders could adjust, but too fast and they burst.  They can also become disconcerted when released to the surface and this may help to explain their slowness in swimming back down to their home level.  From the gulls’ point of view, the slower the better; as this allows them to attack the fish in the bag.  From the fishermen’s point of view, the faster the better; as this allows them to get the whole catch on board in an undamaged state – the customers tend to dislike battered fish with speared chunks taken out of their sides!  Arguably the seabirds do not rely on an abundance of fish deposited on the surface by a boat.  This happens naturally when prey species are hunted by faster hunters e.g. tuna who drive the shoals to the surface and coincidentally into the beaks of the gulls.  The only real problem here is that, without the trawler, these fish would probably have lived to see another day and even spawn, before becoming dinner for other marine inhabitants.

Hugh Fearnley-Whittingstall is correct in that it is daft to throw dead fish/sea creatures back into the sea, in terms of human food.  However, if one brings the by-catch ashore, then another very real problem springs to mind, concerning what it is right to do with it i.e.  If the fishermen land this extra catch and sell it, then they are benefitting from the fish that they should not have caught in the first place!  With our huge population, it is difficult enough as it is to maintain fish stocks with enough adult fish, of mature size, to optimise breeding.  I fear that if the fishermen find that they can actually earn an income from the extra catch, then they will do so – after all the human population is now so huge that all that they catch will be eaten.  Unfortunately, the likely result is that even more species of fish and marine organisms will end up on the critical list.

Perhaps the answer is to ensure that any extra catch is taken into custody on the dock and distributed to local fishmongers for the cost of the distribution exercise only.  That would actually have the benefit of providing more jobs for humans, but then of course they would have to be paid out of the sale of the by-catch, with the result that they too would be hoping that the by-catch was as large as possible.  If the fishermen are fined, then they will simply dump the catch at sea as before!

It’s a difficult question.

Buoyancy Matters: Fish in general have a specific gravity of 1.07 and so will tend to sink in water, unless they keep swimming.  This is no problem for predator fish such as mackerel, sharks and indeed rays; but for those that feed in the plankton, neutral buoyancy is an advantage meaning they can stay at the same level as the plankton without having to expend extra energy on maintaining their level in the water column – plankton move up and down according to the light levels.  This neutral buoyancy is achieved by the presence of a swimbladder (air filled bladder) whose pressure can be adjusted to suit the feeding requirements.  Most young fish can adjust the volume of their swim bladders by actually swallowing air from the surface, and in some species this ability is retained in adulthood.  However, in many species of adult fish this duct closes and the volume is adjusted by the removal of gases from the blood.  Since most fish can survive out of water for a short while, provided that they are kept wet and cool; most are returned to the sea alive.  However, whether they will survive or not, depends on the factors mentioned above; plus whether the benthic species can survive the sudden decompression from several atmospheres up to the surface at an air pressure of only 1 atmosphere.  Some fish with swimbladders have been found at depths of over 4000m depth.  For each 10 metres of depth, the pressure increases by 1 atmosphere; so at a feeding depth of 100 metres the water exerts a pressure of 10 atmospheres.  This means that when these pelagic fish surface, the gas in a closed swimbladder expands 10 times and will definitely burst the organ before it reaches the surface.  Even a swimbladder that is connected to the mouth relies on the fish being able to burp out gas fast enough to avoid bursting the swimbladder.  Non-ducted swimbladders are filled with gas from the blood, which implies that their adjustment is normally slight/slow; and big changes in the volume of gas required would take a long time to achieve.

Once on the surface, another problem arises as the fish has to refill its swim bladder adjusting the fill to the increasing pressure as it moves back down.  If only the surface air were available, then obviously as the fish swam down this would be compressed leaving a very deflated swimbladder.  In turn this could cause displacement and abnormal compaction of the internal organs.

Apart from these problems, the swim bladder of some species contains the normal gas mixture of nitrogen, oxygen and carbon dioxide in ratios that differ not only from the air, but also from those in the water at their living depth.  Thus the ratio of nitrogen in a cod’s swimbladder may vary from 7.6% to 56% with associated percentages of oxygen of 76.6% and 30.1%; and carbon dioxide of 15.8% and 13.9%.  All this is managed by a specialized rete mirabile type structure of the supplying blood capillaries – a similar structure is used to cool the blood going to the feet of penguins and to warm the returning blood so that the core temperature is not affected unduly.  Nature is very good at re-using good ideas.