4 
Bulletin of the EANHS 28( 1) 
Time Interval 
Figure 2 Results of counts of the Indian House Crows crossing towards Mombasa island at the four 
observation points during the different time intervals (date: 28 August 1995). 
aggregations of crows, but in most cases it was hard to 
assess if these birds roosted on Mombasa island or 
elsewhere. 
DISCUSSION & CONCLUSIONS 
This study provides the first detailed record of numbers 
of Indian House Crows around Mombasa. The total 
number of crows that was counted (19,616 birds) does 
not include the resident crow population of the Mombasa 
island itself, but only concerns birds that arrive here 
from elsewhere for gregarious roosting. The resident 
crow population of Mombasa (those that do not leave 
the island during the day) has yet to be studied. Around 
six other small roosts exist at Shanzu, Nyali, Bamburi, 
and Kisauni (P. Burton, pers. comm.). These roosts are 
much smaller than the Mombasa one, usually consisting 
of about 300-600 birds. 
Preliminary observations by the first author (with P. 
Burton) indicate that the crows arrive from as far as 
Kikambala (20 km from Mombasa) in the north and Tiwi 
(c. 20 km from Mombasa) in the south, Ryall (1992) 
reported that it is not uncommon for crows to fly up to 
20 km on foraging expeditions. If this is extrapolated 
similarly 20 km to the west (that is up to as far as 
Mazeras and Rabai), then the total area from which the 
crows arrive for gregarious roosting in Mombasa is 
around 800 km 2 . This means that the average density of 
Indian House Crows would be around 24 birds per km 2 
for the entire area around Mombasa (or between 32 and 
35 birds per km 2 in the area north of Mombasa, and 
about 16 birds per km 2 in the area south and west of 
Mombasa). These estimates are very rough but give a 
reasonable indication of the extent of the crow problem. 
In Zanzibar, which has a surface area of about 2400 
km 2 , Tony Archer reported approximately 60,000 crows 
(Anonymous, 1995; Archer, 1995), which is equivalent 
to an average density of at least 25 birds per km 2 
(although the birds seem to have been more common at 
residential areas along the coast and rarer in the inner 
pans of the island). 
In this study, it was not established where exactly 
the crows gather in Mombasa after arrival on the island, 
but preliminary observations (by the first author) indicate 
a rather scattered distribution with a strong preference 
for large old trees, such as can be found near the Railway 
Station, around Treasury Square, Coast General Hospital 
and in parts of Old Town. Ryall (1992) mentions that 
Mombasa island probably contains five or six large 
roosts. The fact that the majority of the crows arrive 
from the mainland north is noteworthy. This area (in 
