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The Peregrine Fund Notes From The Field
Back after a break, Lake Naivasha’s woes continue.
Shiv Kapila — in East Africa Project    Share

After what seems like five very long months, I am back at Naivasha for another six-week stint (I have been here for four weeks, but regrettably, have fallen far behind on updating these blogs) looking at the lake’s fish eagles. The analysis and write up of the data I compiled when I was last here went very well, and I have since graduated and received an Msc. in Conservation. It’s come in good time too-I managed to leave London just as winter was setting in!

Although I am staying at the Elsamere Field Study Centre again and surrounded by familiar faces, much has changed here. For a start, I have decided to change boats-previously I was using a boat supplied by Oserian, a large flower farm bordering the lake, but owing to their water abstraction and how much damage is caused by their practices, I have opted to use a boat owned by a local tour guide. This boat has been leased to me at the same price but with none of the accompanying ethical dilemmas.

The effects of the (still) ongoing drought are devastatingly apparent. Even in the more stable, steeper shored areas of the lake, jetties have to be extended, large areas of shore are now lying exposed and huge tracts of Papyrus fringe have been stranded. The lake is in a sorry state. As a result of all of this the waters are saturated with sediment and the lake’s colour is now a deep orange, possibly from algal blooms due to eutrophication; the abundance of alkaline-loving lake birds such as Greater Flamingos, Pied Avocets and Cape Teals attest to this fact.

This, however, has proven to be a blessing in disguise to our fish eagles–even though the waters are shallow, opaque and further still from the treeline, inhibiting their ability to catch fish, the increase in waterfowl numbers has provided a bountiful food source for them. On numerous occasions I have stumbled on a freshly killed, recently eaten flamingo carcass while walking along the shoreline; enough food to supply a pair of eagles for a good few days.

At this time of year a lot of other migrants also appear on their southward journeys to warmer climes, though this is unrelated to the state of the lake, but something that happens annually. In the last month I have counted 27 different species of raptors, especially small falcons and kestrels, which are here in huge numbers.
One of the major changes has been the increase in juvenile birds since I was last here. I had observed some pairs incubating last time I was here and these offspring have now fledged, but still hang around in their parent’s territories. I have counted about 11 juveniles out of a population of 113 eagles in total, representing about 10% of birds. This is a marked improvement and no doubt their survival rates have been increased by the high water fowl numbers. Over the past month I’ve also been able to collect eggshells from underneath recently active nests. These will be sent to an ‘Oologist’ to determine if DDT residues could be blamed for breeding failures (This is unlikely as low levels, too low to have a significant impact, have been found in previous studies, but due to the feeding habits of introduced Common Carp, a fish species that now forms a large proportion of an eagle’s diet, which stir up sediment and hoover up any old Lead Shot (the area was hunted extensively for its waterfowl in colonial days) this may have changed). For the most part, breeding failures are as a result of predation, mostly by baboons and monkeys. A couple of eggshells I have collected were of eggs eaten by Vervet Monkeys, barely an hour before I got to that particular nest.

The lowering water levels and contracting shorelines also mean that there is more territorial tension between fish eagles. Their territories shrink as the circumference of the lake shrinks and so more territorial bouts occur.  A couple of weeks ago a pair in good habitat (the best territory in my opinion-dead Acacias bordering the lake, waterfowl in abundance and a fantastically built nest to boot) were replaced by a new, wandering pair. I saw the females of both pairs ‘talon-grapple’–in mid air they lock talons and play ‘chicken’–this often ends in the death of one or both birds if they let go too late and end up crashing to the ground or into the trees. In this case the female of the established pair plummeted into the Acacias (very thorny) and did not get up. I can only assume that her partner was killed in a similar fashion a few days later.  I haven’t seen either of them since and their juvenile is also missing, probably chased off by the incoming pair.

Another such incident happened about three weeks ago. Late one night I got a call about an injured bird down the road at a fishing village. I scrambled a lift to pick it up.  It turned out to be a female fish eagle in an area where it shouldn’t have been-each pair on either side of where I picked it up was complete and it was unclear where this one had come from. A quick scan for injuries yielded none (but it may have been attacked and brought down by an adjacent pair, left to struggle in the mud until it was picked up by a couple of considerate fishermen), but as the eagle was sopping wet and caked with mud, I brought it back to Elsamere for the night. The next morning she had recovered her strength (she showed me this by nipping me in the face, but luckily my beard bore the brunt of the attack and prevented severe damage) but still could not fly because of the muddy feathers. A few days to recuperate and preen at a friendly raptor rehabilitation ‘clinic’ (Mrs. Sarah Higgins’ Sanctuary for Little Owls in Naivasha) sorted her out. This eagle was released a few days later, with no harm done and a ring attached, but it goes to show how much stress there is between territorial pairs and unwanted stragglers.

In the last week or so I have been allowed to start trapping and ringing eagles on my own, a practice which has been as frustrating as exciting, but after three days of trying I finally broke my duck. My first successful attempt was an old male on the western side of the lake. This eagle was very docile for a change and I managed to process it with help from Mash, my new boatman, in very quick time. This eagle already had a ring on it which was clearly attached a long time ago. Further investigation revealed that this bird was rung by Munir in 1997, and has kept the same territory for the last 12 years at least; a tough old bird, something quite rare here–of about 60 birds ringed in the last 12 years, about 15 have been found dead, representing a very high mortality rate and indicative of declining populations. I’ll keep you posted.

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