| dc.description.abstract | This study was carried out from October 1984 to September
1985 at Mwea Irrigation Scheme (M.I.S.), which covers an area of
12,145 hectars• This study aimed at:-
(I) Determining whether significant damage was caused to the
rice crop by birds, particularly Quelea quelea, when ln
large populations.
(2) Determining the side-effects of Fenthion (organophosphate
pesticide) spray when used as a control measure on the rice
pests, particularly on Q. quelea and other bird species.--
Irrigation-fed rice cultivation covered 6 I' "·0hee tares and
2,500 hectares in 1984 season and 1985 season, respectively , The
rest of the area in'both seasons was under various land uses.
This study covered two rainy seasons: October - November 1985 and
March - May 1985 and two dry seasons: December 1984 - February
1985 and June - September 1985.
Monthly population estimates of birds were obtained by transect
counts. Birds' population sizes fluctuated with seasons, and was
most spectacular in Q. quelea P. rubiginosus E. Qlbonotatu$~ and
Dendrocygna bicolor. These population fluctuations were largely
due to migrations into and out of M.P.S., presumably due to changing
conditions of the feeding and breeding grounds. The rates of these
population changes, particularly in the common grain-eating birds
suggested that breeding and mortality were not significant factors
that influenced the fluctuations.
Diets of birds were investigated by crop contents analysis of
the mist-netted birds. The principal food types of the grain-eating
birds
were rice, grass seeds and incidentally, animal matter.
Availability of rice, grass seeds and cereal crops other than
rice was influenced by rainfall and agricultural practices at
M.l.S. Most of the grain-eating birds ate rice more frequently
and at higher amounts than grass seeds even during periods of high
grass seed abundance. This suggests that these birds preferred
rice to other available seeds.
Generally, the grain-eating birds profited physiologically
while in M.l.S. Data on body fat deposit suggests that birds
fattened while at M.l.S., but data on daily and monthly body weights
were insufficient to conclude whether significant changes occurred
while the birds were at M.l.S.
Different methods of estimating damage to rice by birds gave
different results. The shortcomings of each method are discussed.
Overall damage to rice due to birds was higher in the 1984 season
than in the 1985 season despite the significantly higher birdpressure
Ln the 1985 season than in 1984 season. Damage to rice
occurred from the "milky" phase to harvest time. Generally, the
levels of bird damage to rice was not found to be different at
varying distances from birds'- roosting nests mainly the reed
marshes. Out of the 87 bird species o.b.served at M. I.S., only a
few were found to be rice pests, and their importance in terms of
the amounts of rice they ate is as follows:- E. aZbonotatus~
. Q. quel.ea, P. rubiqinoeue and P. cucul/latue, The other bird
species were regarded to have caused no significant loss. The
total loss of rice attributed to bird action in both seasons was
3,142 tons, which was about 10% of the total yields.
The
population of Q. quelea which exceeded 100,000 individuals
per bird-day in September 1985 when rice was most vulnerable to
these birds prompted attempts to reduce their number by spraying them
with Fenthion. It was assumed that such action would reduce the
estimated high losses of rice. The Fenthion spraying had
important biological and economic implications. Q. quelea were
sprayed at sites where they assembled in large roosts often with
many other non-target bird species. Thus, non-target birds were
killed when the quelea roosts were being destroyed. Other
hazards that might have occurred to the birds and to the biosphere
in general within the spraying sites and their proximal zones were
not studied.
This study brought to light the conflict that existed between
the principles of rice protection from bird damage and that of
conservation of wildlif e in using toxic Fenthion at N.1.S. It 1S
suggested that in future, the ecological and economic implications
of employing toxic pesticides such as Renthion as a bird control
strategy should be fully evaluated be(ore and after they are
implemented. | en |
