Carnage at Long pool

In the morning, as expected, we failed to locate the lions again but, driving over a small bridge nearby we found about twenty marabou storks (Leptoptilos crumenifer) congregated by a pond of green stagnant water. That was all that remained from the stream that flows there during the rainy season. As soon as we stopped they slowly moved away to what they considered to be a safe distance from us, away from the water. We moved off to a bend in the dry riverbed to watch them undisturbed. As soon as we withdrew they returned to the pool and resumed their activity.

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The first group of marabou storks we saw.

The storks were feeding on stranded fish, probably catfish judging by the frequent rises they made to breath on the surface, opportunity immediately taken up by the storks that would rush towards the water movement ready to snap one up. We left them undisturbed and continued with our drive. A couple of hours later when we returned they were gone but there were still fish there. The African sharptooth catfish (Clarias gariepinus) are special in that they can bury themselves in the mud when the water evaporates and they can also survive in muddy water as they have a special breathing system that they can use in addition to their normal gills.

However, I am sure that despite their toughness the catfish days were numbered as the next rains will only come in December if the rains are good, far too late for them. At that time the ground would be bone dry. It was surprising that the marabous had abandoned what looked like easy food but we are used to Nature’s ways!

We soon forgot about the storks as we continued with our quest for new sightings. Our hopes of finding the lions seemed to revive when we found their fresh footprints. Judging that they had been left there during the early morning we tracked them for a long while, trying to guess what their aim was, only to lose them when they moved away from the road. Following lions on foot through the bush and without an experienced ranger is not recommended so we decided to leave them alone. As it happened, they eluded us for the rest of the trip.

We normally do not see large elephant herds at Mana Pools. Some family groups come together at the height of the dry season while staying near the river. At the time of our visit, although the rains had not been abundant, there was still water inland and the elephant population was still spread out all over the park. The few elephants we saw were the usual resident bulls that seem to hang around the shores of the Zambezi. It was one of these that we found that morning and we derived entertainment watching it stretch for the apple-ring acacia branches and leaves. The pods, their favourite food later on in the dry season, were still small and immature so they were not the elephants’ target at the moment.

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A bull elephant stretches to feed under the special Mana Pools light.

Returning to camp at about eleven, we saw a large number of yellow-billed storks (Mycteria ibis) in one of the smaller segments of Long pool that usually dries up during the dry season. There was clearly something special going on that attracted such large number of birds so we decided to go and have a look. Getting closer we saw that there were also African spoonbills (Platalea alba), a few herons and also a few marabou storks. “So here they are”, I thought while stopping the car to get closer on foot.

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We saw a large number of storks congregated at Long pool.

The pool was full of birds and it appeared that mostly the yellow-billed storks were -again- catching other shoal of stranded fish.

They seemed to be alternatively “driving” the fish towards one of the narrow and shallow ends of the pond and, once there, they would pounce on their victims. Both the yellow-billed and the marabous seemed to be on the same wavelength and after fish. The few African spoonbills present, however, continued wading in their usual fashion as individuals and they did not seem to take any notice of the other birds.

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The yellow-billed storks chasing the fish in a coordinated fashion.

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Marabous waiting for the right time to join in.

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African spoonbill.

At first we assumed that the prey were catfish as we had seen earlier at the small bridge and on other occasions in Kenya (Maasai Mara) and Mozambique (Gorongosa). We soon saw, however, that this time the victims were silvery fish of 5 to 15 cm that were being picked in large numbers by the birds. Whether they were immature Chessa (Distichodus schenga) or Nkupe (Distichodus mossambicus) both common inhabitants of the lower Zambezi, or perhaps some other small fish I could not be sure. It was interesting to note that, as the pool was dry last year, the fish must have come in during the wet season through a connection between the pool and the Zambezi.

The yellow-billed storks outnumbered the marabous about 10:1 and they strode in groups following what looked like a cooperative fishing strategy. They would wade together towards one end of the pool driving the fish in front of them and then they will pick them from the reduced area they had created. They fished in their usual fashion; by placing their half open bills inside the water and snapping them shut when feeling a touch through a very fast reflex. They frequently caught fish but if they missed they would do a short chase that soon ended with or without a fish being caught and back to their feeding posture.

While this would take place, the marabous watched like smartly dressed supervisors. The moment the fish were trapped they would lose their bogus formality and join in the feeding frenzy with gusto! They would jump or fly in spreading their wings to make room for themselves submerging their heads under water to catch the fish. Often their feeding enthusiasm would be such that they would plunge almost totally in pursuit of the fish. Many of them had their gular sacs[1] inflated and probably their pouches full of fish. Many of them were also flashing a bright red bubble-like sack at the back of their necks, probably a consequence of their excited condition!

Although we witnessed the occasional confrontation between the two stork species, these were minor incidents and we saw no physical contact.

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A brief stand-off or “don’t step on my toes”

Conversely, there was a lot of interaction among the yellow-billed storks in the form of bill clattering, chasing and jumping facing each other. Occasionally the opponents would interlock their beaks as if involved in some kind of courtship. All these encounters were of short duration and the temporary “rivals” quickly got back to feeding. The grey immature yellow-billed storks congregated at the periphery of the pond, not taking part of the adults’ activities but trying their fishing technique as best they could where there were clearly less fish and I did not witnessed any catch.

While the collective fishing took place, a pair of fish eagles, perched on a tall dead tree, watched the storks attentively. They called regularly and, from time to time, they would swoop down among the alarmed storks and, at least once, one of them managed to snatch a fish although we could not see if it caught it itself or it robbed it from one of the fishing storks.

 

The following video gives a dynamic view of what we witnessed.

Note: I recommend that you watch it first as it is and then you use the cog wheel at the bottom right corner of the screen to slow it down and see things with more detail.

 

 

[1] Later, reading about marabous, I learnt that the large sacks that hang under their heads are not crops but gular sacs. The latter are cooling devices as well as used for displaying purposes.

Note added on 3 July 2016. One of the pictures above shows what I thought was a confrontation between a Marabou and a Yellow-billed stork. I saw that the Marabou was rather indifferent but I thought it was because of its size. However, looking at the picture again, I realized that the Yellow-billed stork was swallowing a fish! Additionally, the fish looks like a young Tilapia so the birds may have been feeding on these rather than on the other possible species I mentioned. Bushsnob

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