As the person who set the ball rolling, I now maybe need to rephrase my
queries once more, since part of the discussion (which I have followed with
great interest) has meandered away from the original questions. These were: 1.
Why is the density of birds so low in the Madagascar forests?, and 2. Why are
so very many birds on Madagascar extreme skulkers, compared to other areas?.
Question nr 2 has remained unanswered and virtually undiscussed, apart from
some jokers who suggested that all the non-skulkers had been exterminated by
now. (Several of the most common birds on Madagascar are conspicuous and
unafraid, so that can't be the answer.) Question 1 HAS been discussed, but many
people seem to be under the impression that I asked about the low biodiversity
on Madagascar---our trip tallied 185 species in almost a month of birding all
over the island. But that was not my question, as I feel I understand that.
Madagascar, though large, is a long isolated island, and it therefore OUGHT TO
have low diversity, and it follows this rule nicely. In the same way, the very
high degree of endemism is easily understood, and again is a function from the
long isopaltion of the island and the considerable distance to mainland Africa.
Only a few species have managed to reach Madagascar, and in some case there has
afterwards been a modest local radiation, of which the couas and the vangas are
the best examples. In the case of later influxes---one tends to think-- the
madagascar birds have diverged from the mainland forms into a new species.
Examples are the local drongo, kingfisher, Cisticola, lark, gymnogene,
cuckoo-hawk etc etc. And still later immigrants also exist, and in those cases
the Malagasy representatives are either well-marked subspecies (some herons,
the roller), or even not clearly different at all.
Somebody asked how many of the endemic species we have seen on the trip, and
the answer there is: almost all, except some notoriously rare ones, such as the
Red Owl, the Serpent Eagle,berneir's Vanga, or the recently rediscovered Mad.
Pochard. personally I missed three more: Pollen's Vanga, the yellow-bellied
Sunbird-Asity, and the White-throated Oxylabes, but all three were seen by at
least a few of our group. As I said before, both the Rockjumpers guides and the
local guides are highly competent!
So my original question was not: Why are there so few bird species?, but: Why
are there so few birds? The answers I have got fall into two categories: 'All
rainforests are like that', or 'The people have destroyed the area'. I feel
that both contain a grain of truth, but neither can be the entire answer. there
is no doubt about the sad fact, that Madagascar has suffered greatly from
unwise agricultural methods, and recently (although with 22 million people the
country is not really overpopulated as yet) from too great fecundity and too
many people. It is a very sad sight to watch from a plane and see all the
denuded hills with deep erosion gullies, and all the red- or brown-coloured
sluggish rivers transporting all the good topsoil into the sea. Or all the
sacks with charcoal being sold along the roads and stemming from continued
onslaughts on the remaining forest areas, especially the fantastic spiny forest
and other dry fiorests (Zombitse!) And of course that must have had
repercussions for the birds, and what we do now, when on a birding trip, is
trek from one forest remnant to another, and pass over the large denuded areas
as quickly as the often atrocious roads permit. But: many of the se remaining
areas are still very large indeed, especially in the wet rainforest covered
eastern part of the island. So large, that I can not quite believe that the low
density of birds there is primarily a function of the destruction of other
areas on the island.
My experiences with other rainforests are modest. I have been quite a lot in
Australian rainforests, and otherwise in New Zealand, Costa Rica and Ecuador.
in these areas I have of course noted the 'feast or famine' regime that they
offer to birders: long periods with little to see, and then suddenly a large
mixed flock with almost too much to choose from. Still, in my (I agree very
limited) experience this was still different from what I experienced in
Madagascar (Although New Zealand comes closest), here one could walk for e.g.
half an hour in wonderful climax rain forest, while all the sounds one heard
were the occasional frog call, and the evocative whistles of the Cuckoo-Roller
far overhead. And when we finally came across a mixed flock (which happened to
me only twice), they were maybe 10-15 vangas , a cuckoo-shrike and a paradise
flycatcher. I definitely had the impression that there were fewer birds here
than in the other rainforests I have visited. And interestingly enough this
impression was strongest during our Masoala-extension, when wevisited the
largest remaining almost undisturbed forest on the island!
So my questions still stand: Why are there so few birds in the island's rain
forests, and Why are so disproportionally many birds on Madagascar extreme
Wim Vader, Tromsø Museum
9037 Tromsø, Norway
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