_The breeding season in North Borneo._--Birds in the Quoin Hill area of
eastern Borneo seem to breed most commonly in June, July, and August.
Table 2 lists 34 of the more common species at Quoin Hill for which
evidence on breeding was available. The actual evidence was provided by
females with active brood patches or active ovaries, males with enlarged
testes, birds in juvenal plumage, or birds actively in annual molt. From
such data dates of presumed breeding were extrapolated. In Table 2, the
solid black lines indicate dates for which both male and female were in
breeding condition. The dotted lines indicate enlarged testes but no
evidence of breeding in females. In the bottom line of Table 2, the
figures indicate the percentage of the population breeding in any one
month. For instance, 2.9 per cent of the birds were breeding in March,
but 73 per cent were breeding in June. Rainfall records from the Cocoa
Research Station from April, 1959, to December, 1964, were available to
me. These data, along with the average for each month, are given in
Table 3. There appears to be little correlation between rainfall and
breeding season at Quoin Hill. A true dry season in the Quoin Hill area
does not occur, but monthly rainfall has varied from 0.57 inches to
21.27 inches in a single year.
TABLE 2.--Seasonality of common breeding birds at Quoin Hill. Solid
lines indicate times of occurrence of known breeding; dotted lines
represent times of presumed breeding.
============================================================================
SPECIES | J | F | M | A | M | J | J | A | S | O | N | D
----------------------------+---+---+---+---+---+---+---+---+---+---+---+---
_Treron curvirostra_ | | | | | | | ....-----| | |
_Cacomantis merulinus_ | | | | | | | | --------..........
_Chalcites malayanus_ | | | | | | -------- | | | |
_Phaenicophaeus | | | | | | | | | | | |
curvirostris_ | | | | | ------------ | | | |
_Collocalia fuciphaga_ | | | | | | ..------ | | | |
_Chaetura leucopygialis_ | | | | | ------| | | | | |
_Harpactes diardi_ | | | | | ------------.... | | |
_Eurystomus orientalis_ | | | | --------- | | | | | |
_Calorhamphus fuliginosus_ | | | | | | -------.......| | |
_Megalaima chrysopogon_ | | | | | | | --------- | | |
_Megalaima mystacophanes_ | | | | | | --------..... | | |
_Sasia abnormis_ | | | | | ------- | | | | |
_Micropternus brachyurus_ | | | | | -------- | | | | |
_Dryocopus javensis_ | | | | |-------- | | | | |
_Pycnonotus cyaniventris_ | | | | | | | | | -------- |
_Pycnonotus atriceps_ | | | --------- | | | | | | |
_Pycnonotus brunneus_ | | | | | | ----------------- | |
_Pycnonotus | | | | | | | | | | | |
erythrophthalmus_ | | | | | | -------- | | | |
_Zoothera interpres_ | | | | --------- | | | | | |
_Malacopteron magnirostre_ | | | | | --------- | | | | |
_Ptilocichla leucogrammica_ | | | | | | ------------ | | |
_Kenopia striata_ | | | | | -------...| | | | |
_Stachyris maculata_ | | | | | ----------| | | | |
_Orthotomus atrogularis_ | | | | | | ----------------- | |
_Orthotomus sericeus_ | | | | | | ------------- | | |
_Orthotomus sepium_ | | | | | | ----------------- | |
_Rhipidura perlata_ | | | | |-------- | | | | |
_Prionichilus xanthopygius_ | | | | | | | | ---------------
_Anthreptes rhodolaema_ | | | | | | --------- | | | |
_Arachnothera flavigaster_ | | | | | | | | | | | ------
_Pityriasis gymnocephala_ | | | | | | | | | | ----------
_Oriolus xanthonotus_ | | | | | ---------- | | | |
_Platysmurus leucopterus_ | | | | | ---------- | | | |
+---+---+---+---+---+---+---+---+---+---+---+---
| J | F | M | A | M | J | J | A | S | O | N | D
The percentage of breeding +---+---+---+---+---+---+---+---+---+---+---+---
in any one month is as | | | | | | | | | | | |
follows: | 0 | 0 |2.9|8.8| 38| 73| 58| 50| 35| 17| 11| 8
----------------------------+---+---+---+---+---+---+---+---+---+---+---+---
Birds in the moss forest near Tenom appeared to be breeding in January,
paralleling the trend found by Voous (1950a) for the lowlands of Borneo.
_Other Bornean observations._--Voous (1950a) summarized data assembled
by Coomans de Ruiter on the breeding of birds in the lowland of western
Borneo near Pontianak. It appears that the breeding season in that part
of Borneo, and indeed in all of western Borneo (Banks, 1950), starts in
December and reaches a peak in March.
TABLE 3.--Monthly rainfall records, Cocoa Research Station, Quoin Hill.
==============================================================================
Year |Jan. |Feb. |Mar. |April|May |June |July |Aug. |Sept.|Oct. |Nov. |Dec.
------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
1959 | | | | 6.49|12.16|11.11| 7.64|12.11| 4.75| 8.33|12.10|13.81
1960 | 9.24| 8.17| 3.76|10.65| 8.84|11.00| 6.31|11.25| 8.56| 5.49| 8.39|11.81
1961 | 6.68| 8.06| 4.35| 4.74| 7.55| 7.25| 5.93| 2.40| 7.47| 5.58| 4.38|10.73
1962 | 3.82| 6.76|13.72| 9.68| 6.82| 7.49| 6.59| 5.82| 7.81| 9.47|19.80| 9.28
1963 |21.27| 8.18| 7.64| 0.57| 5.83| 4.62| 0.64|12.49| 5.24| 8.75| 7.43|11.05
1964 | 4.17| 7.92| 4.40|11.20|11.82| 8.04| 2.42| 7.52| 5.69|13.15| 8.82| 9.88
Avg. | 9.03| 7.81| 6.77| 7.22| 8.83| 8.25| 4.92| 8.59| 6.58| 8.46|10.15|11.09
------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
Gibson-Hill (1952) has questioned Banks' (1950) interpretation of data
from the egg collection of V. W. Ryves. Gibson-Hill has shown that the
data collected by Ryves covered two widely separated localities, one at
Kiau near Kota Belud and the other near Sandakan. The former locality is
on the west coast of North Borneo and the latter on the east coast of
North Borneo. Gibson-Hill points out, and rightly so, that the timing of
the rainfall in different parts of Borneo must be taken into account
because of the large regional variation. The nesting data from the Ryves
egg collection are scant and when used alone possibly yield a distorted
view of the actual breeding season. Ryves did no collecting in the
Sandakan area between September and March, and in the Kiau area between
May and January. Although the breeding data from North Borneo
accumulated by both Ryves and myself are limited, and records of
rainfall are scant, there appears to be a trend toward breeding after
the heavy rains have fallen.
_Seasonality of breeding in tropical birds._--Possibly Bornean birds
breed mostly in the "driest" part of the year. If so, this is in
contrast with the time of breeding of birds of other tropical areas.
Moreau (1950) found that in the Congo there was no distinct breeding
season for most groups of birds, but that in East Africa there was a
double breeding season; the peaks coincided with the two rainy seasons.
Lack (1950) found that the Geospizinae of the Galapagos breed only when
it rains and that rainfall causes a flurry of nest building and singing.
If the rains stop, then the courtship activities stop until the next
rains. Miller (1963) found that in birds of a western Andean cloud
forest the breeding season was spread over the year and that breeding
could not be correlated with rainfall.
Obviously more study is required on breeding of birds in Borneo before
the timing of the annual cycle can be ascertained.