A rough calculation

May 12th, 2013

I find by a rough calculation from Bering’s data that the longi­tude resulting from his itinerary from Tobolsk to Okhotsk is 77° 36′ E. The distance in a straight line is about 2,390 miles, but by the route Bering traveled the distance is a little more than 3,746 miles. The longitude in Bering’s List of Positions is 76° 07′, which differs from the pedometric measurement by 1° 29′ (or about 45 miles). On Bering’s map, Okhotsk is located in longitude 74° 30′ E. of Tobolsk, while the most modern observa­tions for Okhotsk put it in 142° 40′ E. of Greenwich or 75° 40′ E. of Tobolsk. So that Bering’s pedometric measuretent was nearly 60 miles in excess ; his revised table (as corrected by the eclipse ?) 27 miles in excess ; and his map about 30 miles in error in the opposite direction. These discrepancies show the inexact­ness of the methods then in vogue and also that the pedometric method was not very much worse than the others in its results.

ship2Although there are several typographic or other errors in his table of itinerary which render exact comparisons impossible, it may be said that the error of the pedometric method, including the passage by sea from Okhotsk to Kamchatka, averages about two degrees or sixty geographical miles. In the cases of Okhotsk and Bolsheretsk the error is one of excess ; in the case of the cape at the mouth of the Kamchatka river and of the turning point of the expedition north of the apartmentsapart holiday rentals, the result is too small by about the same amount.

That his chart and his revised list of positions should differ as they do, is quite as likely the result of the careless way in which the minutiae of such work were generally regarded at that day, as to any difference of date, or of intentional modification.

To conclude our review of the instrumental means and methods then in use, it may be said that the compasses in use at that day were comparatively roughly made and more or less inaccurate. The variation was determined in a given latitude by the azimuth of the Polestar or the sun at setting observed by means of sights attached to the rim of the compass, which was a method accurate enough for the general purposes of navigation. The distance run was measured on shipboard by the log which was in about the same form and perfection as at present, being a very ancient invention.

The survey of a general coast-line was made by compass bear­ings on prominent points, repeated from successive stations, the distances of the ship’s course being determined by the log and the courses by compass, with corrections for current and the varia­tion. The lines thus obtained were checked by latitude observa­tions made with Davis’ backstaff when the weather permitted.

Apart from any of the methods mentioned it seems to have been overlooked that Bering might have corrected the longitudes of the N.E. Siberian coast by the ordinary dead reckoning kept on board his vessel, provided he started by adopting the longitude for the southern part of Kamchatka peninsula which was in com­mon use on many of the charts of his day.

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The Family Life of the Pink-Backed Pelican

October 15th, 2012

Within seven to ten days of hatching the change was enormous. The nestlings no longer needed to be brooded all day as they were now covered by a white down and had grown to the size of a duck. They sat or stood in the nest while the parent stood guard on a branch above. The parent occupied the time preening its feathers, or it just tucked its head between its shoulders and went to sleep. Occasionally it threw its head in the air, opened its beak and tautened the great pouch until you could see every vein.

By about 7.30 each morning all the adults except those with young chicks had gone off to the lake to fish. As the morning wore on the young pelicans became more and more noisy as their hunger increased, and they stood eagerly watching for their parents. The pouches below their beaks pulsated with ripples of light as the sun shone through the translucent skin, while they thrust forward their heads in a begging action accompanied by a sound suggestive of snarling and groaning. At the height of the breeding-season, when there were several hundred young birds, this guttural snarling sound was tremendous. It could be heard far off as you approached the pelicanry and was intermingled with a clacking sound made by birds tossing their heads in the air and smacking their great beaks shut. Sometimes, on arrival back at the nest, birds would also clap their beaks along that of their mate. Apart from this clapping noise we never heard any sound uttered by the adult pelicans. The snarling came entirely from the young birds and reached its height towards midday when the parents began to return from Lake Victoria.

pelican

We could distinguish the birds coming from the lake from those just soaring round the sky for the pleasure of flight, for the former came in at a great height. They would first be seen as specks in the sky and then appear to roll over—rather like the victory roll of Air Force pilots returning from a successful mission—and come down in a long sweeping spiral. They never landed right on the nest, but alighted on a branch a little distance off and stayed there for some minutes in the most tantalizing fashion while their young got frantic with hunger. Although we could not differentiate between individual birds, the offspring could always recognize their parents as they flew in. I think that the parent during this interval may be regurgitating the fish, for they do not bring it in the pouch as we expected, but in the crop.

pelican

Suddenly the parent would drop down to the nest and the most exciting part of the day began. The very young chicks just ate up scraps of fish dropped by the adult onto the nest, but within thirteen days they fed direct from the parent’s crop. Leaning back on its rump, with immature wings agitatedly flapping to keep its balance, the chick would reach right up into the parent’s pouch. The parent then stretched its head for­ward so that the youngster could push its beak and head well down the long neck into the gullet. It was a great struggle. All that could be seen of the young bird was a pair of moving wings and its stern. As it emerged the parent shook its head as though glad to be rid of the hungry beak.

pink pelican

This was the only meal of the day and there was quiet for several hours afterwards as the replete chicks and fledglings sat stolidly digesting the fish. Sometimes a large fish would stay for half an hour or more bulging part-way down the chick’s neck until it was finally absorbed. Fish dropped on the ground below the tree weighed three-quarters to one pound.

William Congreve, writing in 1695, is more correct in his observation, ‘What, wouldst thou have me turn pelican, and feed thee out of my own vitals?’, than Mr D. L. Merritt in his poem:

A wonderful bird is the pelican;

His bill can hold more than his belican.

He can take in his beak

Food enough for a week;

But I’m damned if I see how the helican!

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The Life of Pelicans

October 10th, 2012

It seems that the pelicans will continue to use the same breeding-site year after year providing they are not disturbed. This was borne out by the remains of an old nest on one of the fig trees which we used as an observation-point. It was easily climbable and I asked one of the Luo why pelicans no longer nested there. He told me that the last time a nest had been built the eggs had been stolen–not, he emphasized, by any local people—and no pelicans had nested there since.

pink pelican

In East Africa, where there is little change of seasons and no appreciable difference in the length of daylight to regulate the breeding-cycle, birds are often much less ordered in their nesting-habits than in the more temperate countries, where one can say within ten or fourteen days at what time of the year birds of a particular specieswill all start to nest. Here some birds breed in almost any month of the year, while others con­fine themselves to the short rains (November—December) or the long rains (April—June). These pelicans only breed once a year, during the short rains; but the other two records refer to breeding in May, during the long rains, on the Tana River, and in August, between the long and the short rains, at Lamu on the coast.Our observations were greatly helped by the fact that some pelicans in the colony started laying as much as two months later than others. Consequently, on a single visit we might see newly hatched chicks, naked and helpless; active down-covered nestlings, raucously calling for food; and fully fledged youngsters stretching wings to a span of five feet or more in prepara­tion for their first attempts at flight. On December 28, when the platform and the ladders leading up to it were finally completed, one of the three pelicans in direct view had just hatched her clutch of three eggs and the other two were still incubating. On our second visit on January 10 a second lot, two only, had hatched out. As their newly born nakedness had already been covered by white down we estimated that they were about seven days old. But the third clutch did not hatch until the end of January; by then the neighbouring youngsters, a month old, were as big as adult geese. Some of the earlier families on the main tree had already flown.

pink pelican

The pelican incubating the third clutch pre­sented one of our first problems, for we never saw it leave the nest over the period of six to seven hours during which we watched, and I never saw its mate bring any food. The problem was solved on a later visit when my wife was with me and noticed an adult pelican arrive and do a very quick change with the incubating bird, who then flew off towards Lake Victoria while its mate carried on incubating. In the excitement of photographing the feeding of the young pelicans in the other two families I had each time missed this quiet but quick change-over. There is no difference in colour or size between the sexes. The three nests were loosely made of sticks precariously placed along one branch. Two were touching, while the third was perhaps two feet away. There seemed little to keep them in place but the body of the brooding bird. Yet there they remained intact for an incubation period which we estimated to be about thirty-five days, followed by a further sixty days minimum during which the young birds remained on, or near, the nest. The periods which I quote have all had to be estimated to the nearest few days as each visit to the pelicanry entailed a return journey of more than a hundred miles over rough roads. Our observations were therefore made over three months, during which we visited the pelicans every twelve to fourteen days.

pink pelican

For the first few days of the nestlings’ life they peeped out only occasionally from beneath their brooding parent. They fed on scraps of fish which the adult dribbled onto the nest as she stood over them. After they had eaten their fill she would pick up any food that remained on the nest, but we could not determine whether she kept it in her gullet for a future meal for the chicks or consumed it herself.

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The birds in lake Victoria

October 6th, 2012

TWELVE miles inland from the Kenya shore of Lake Victoria, Pink-backed pelicans come each year to breed. A hundred or more pairs make untidy nests along the branches of a tall tree—so tall that I have never been able to reach a spray of its leaves to have it identified.

The birds start to arrive in October. Once all suitable branches are occupied, late arrivals over­flow onto a nearby fig tree. In this we were lucky, for the fig was one of a group of three and the other two were sufficiently close to serve as vantage-points for photography. In each we built ladders up to a platform some sixty feet high. At this height we were roughly level with a group of three pelican families whose life and habits my wife and I observed and photographed over the next three months.

lake victoria pelican

Ordinary bird books, particularly those on African birds, contain little beyond a brief description of the Pink-backed pelican, its food and type of nest. They tell us that it is smaller than the White pelican; that it is peculiar to Africa and the adjacent islands; that it is a greyish-white bird with a distinctly wine-coloured back and rump; that it nests in trees, bushes or even on the ground, fishes singly or in parties, lays two to four pale blue or white chalky eggs, and that nothing is known of its call beyond clacking guttural conversation.

To these bare facts we wanted to add some detail. We wanted to know, among other things, how long the eggs were incubated; whether the cock bird incubated as well as the hen; how the incubating birds fed; how the young birds were fed and how often; the number of weeks the young remained in or, more correctly, on the nest; what calls the pelicans made; and why they chose this particular place.

lake victoria pelican

Pelicans, singly or in parties, are seen on most lakes in Kenya but there are only three other places in which breeding colonies are recorded, all of them several hundred miles away. The White pelican, Pelecanus onocrotalus, which is distributed over south-east Europe, Asia and Africa, is known to breed only on Lake Rudolf in northern Kenya. The Pink-backed pelican, Pelecanus rufescens, has been recorded as breeding only on the Tana River in eastern Kenya and at Lamu on the coast. But, though unrecorded, the colony of Pink-backed pelicans where we made our observations has been known for many years to government officers working in that part of the African Reserve; and the local inhabitants, the Luo, can remember no time when the birds did not nest in the big tree.

At first we found some confusion when discus­sing the birds, for the Luo spoke Kiswahili but used the Luo word mbusi, which in Kiswahili means goat, to describe the pelicans. In Kiswahili we were limited to mwari which, as well as mean­ing pelican, also refers to a boy or girl during initiation rites, a virgin, or a tongue of fire. Or we could use, as we usually did, the more cumber­some ‘kitchen-Swahili’ word which translates as `the bird-owner-of-the-very-big-beak’.

The Luo attached a mysterious significance to the presence of the birds each breeding season and we were told that the local Chief had planted some eucalyptus gum trees near the main tree as an alternative nesting place should the great tree ever die or be blown down.

lake victoria pelican

As the pelican’s diet is mainly fish, a nesting-site twelve miles inland meant a return journey of at least twenty-four miles for every bit of food brought to their young. Those that we saw fishing were mostly far out on Lake Victoria, so one can say that the return trip on average was much nearer thirty miles than twenty-four. Why over all these years had they used this site so far from their feeding-grounds? I can only assume that experience had shown this tree to be a safer breeding-place than any others nearer the lake. All this lakeside area is closely settled and there are few great trees left standing. This particular one had no branches lower than about twenty feet, so it was virtually unclimbable. More­over, in a hollow in the main trunk just below the lowest branches there was a great swarm of bees, which was probably as regular a feature as the pelicans. The African bee is a very fierce insect which regards attack as the best form of defence. I can think of no better protection.

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