Of Fish Eagles and Mistaken Identities
Shiv Kapila— 21 July 2009 — in East Africa Project Share
My last two weeks in the field have proven both productive and interesting. The last eagle count has showed a relatively stable eagle population, but as the rains are conspicuously absent, the lake level is still decreasing and as a result, I’ve had to keep to open water in areas (particularly the north) and try to spot birds from (literally) miles away.
As well as the last count, I’ve also taken recordings of water clarity and distances of favoured fishing perches from the shore. These two variables have an obvious and sometimes substantial effect on fishing conditions. For example, in the north, the tree line is about 1.5 km away from the shore, and the Secchi disk (a pied disk used to measure water clarity) disappears from view only 3 cm from the surface making fishing harder than in the south, where in some places the tree line is at the shore, and the disk can be seen up to 30 cm down.
I also had the good fortune to have use of a car for a day–this was spent motoring around the lake’s perimeter looking for nests, and in the process I managed to meet most of the residents who own large tracts of land around the shore. Thankfully, all were very pleasant and gave me free passage as well as a few pointers as to the exact whereabouts of each nest–they aren’t as easy to find as one may think. In addition to tracking breeding progress, I’ve managed to find some eggshell fragments from Crescent Island. Tests on these fragments might be able show the effects and levels of DDT residues in the ecosystem and whether they affect fish eagle breeding on the lake. DDT is an insecticide, which was widely used in the 1970s, but as it takes a very long time to degrade and it may still be present and has the unfortunate effect of making eggshells thinner if present in high enough levels. Thinner eggshells mean they are much more fragile so they tend to crack and fracture at the slightest disturbance, lowering breeding success rates and consequently impacting entire populations.
Since I finished the counts earlier than I had previously anticipated, I managed to catch up on a few more hours of eagle observation. From the time I spent watching the birds in the best and worst habitats, I can see how each pair is affected by their respective habitat qualities-in poorer habitats, the eagles attempt more strikes, but with a lower success rate than their counterparts in better territories. As well as this, the pairs in poorer habitats spend far more time soaring–they have larger territories than in good habitat as they are less productive and so need to cover much more ground to defend their patches.
In the last couple of weeks the eagles have shown more interest in hippos than usual-during a four-hour observation stint of the most recently trapped eagle, one of the pair made a rather ambitious strike at a hippo’s head, probably mistaking a twirling ear for a crayfish tail. This strike was obviously unsuccessful! The hippo must have seen the eagle coming as it raised its head just before impact; as a result, the bird aborted during its approach and returned to its perch, presumably to recover its injured pride. On another occasion, whilst passing one of the many pods of hippos, I saw what I assumed to be a cormorant perched on one of their backs (they tend to do this), but as the boat got closer to the pod, it was clear that the bird was a fish eagle, using the hippo as a fishing perch. The hippo didn’t seem to mind. I think its exceptionally thick skin (the skin of a large hippo would weigh a ton by itself) meant the eagle could do no damage. A hilarious sight, but it aptly shows how much the eagles are struggling with the low lake level.
Closer to home; things have been just as restless. My Sunday afternoon coffee was interrupted by news of a snake feeding in the Elsamere grounds behind the dormitories. Thinking the snake would just be a grass snake eating a rat I ambled over slowly, camera in hand. Said snake and its meal were nowhere to be seen until, five minutes later, I heard a huge commotion 100 metres away. It turned out that the snake was in fact a 12-foot long python and its prey was a heavily pregnant goat. A snake this large would obviously pose a severe danger to people living in the town close by and so the python was moved to the nearby Oserian wildlife sanctuary (but not before its meal was interrupted and its quarry removed to be eaten by the villagers who found it) by the Oserian security guards.
Now that I've finished in the field, this blog will soon be closed, and now comes the arduous and tedious task of data entry and analysis before the big write-up. If I'm lucky, I will be able to do a follow-up study in a few months in Naivasha, so this may not be the last you hear from me...
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