Malabar Gray Hornbill Ocyceros griseus
Version: 2.0 — Published July 9, 2020
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The birds are monogamous and breed between February and May, occupying cavity nests on large trees. Cavities are formed mainly by wood rot. The female enters the nest and seals the cavity opening with her droppings forming a seal with a slit-like opening through which the male feeds her for nearly twelve weeks. Female molts her flight feathers and rectrices sequentially in the nest. The male feeds the female and chick (typically single); female emerges almost simultaneously with the chick. Breeding success can be high (ca. 90%).
Birds show high nest site fidelity with nest cavities often reused for many years. Of 27 nests located during a study in 1993-94, 10 nests were found to be active in 2018 (31, P. Y. Pawar, D. Mudappa, and T. R. S. Raman, unpublished data). Nest cavities may be abandoned in later years due to expansion or shrinkage of the cavity, predation, occupation by bees, treefall, and fire damage (32, 33, 20).
Breeds from February to May in the Anamalai Hills (24) and the Nilgiris (26). In the Anamalai Hills, the breeding season of the Malabar Gray Hornbill coincides with the peak in fruiting of large-seeded and lipid-rich fruits in the Families Myristicaceae, Meliaceae, and Lauraceae (29). In this landscape, the breeding season also corresponds to a period of higher fig (Ficus spp.) fruit availability in the rainforests (P. Pawar, D. Mudappa, and T.R.S. Raman, unpublished data).
Malabar Gray Hornbills are secondary cavity nesting birds that occupy existing tree hollows formed by branch breakage followed by wood rot or excavated by woodpeckers, more often the former. A majority of the nests are in live trees: 26 of 27 nests in the Anamalai Hills (31); 79 of 81 nests in the Nilgiris (32). Birds nest in cavities formed in a number of different tree species. In the Anamalai Hills, of 59 nests in 26 tree species, nearly half the nests were on Alseodaphne semecarpifolia, Mesua ferrea, Aglaia elaegnoidea, and Artocarpus gomezianus. In plantations, they are known to occasionally nest in non-native tree species such as Grevillea robusta, Spathodea campanulata, and Eucalyptus sp., if the trees are large enough and contain suitable cavities. In tropical semi-evergreen forest of Mudumalai Wildlife Sanctuary, nests were located in 19 tree species, with over two-thirds of the nests being located in Lagerstroemia microcarpa, Terminalia bellirica, and T. crenulata.
The nest cavities are located on the tree trunk or a main branch. Of 59 nests in the Anamalai Hills, 69% of the nest cavities were located on the main trunk, 24% on a primary branch, and 7% on a secondary branch (P. Y. Pawar, D. Mudappa, and T. R. S. Raman, unpublished data). Nest cavities on trees were located at a height as low as 3 m up to 39 m (average 14 ‒ 15 m) from the ground, with the girth of the tree at nest height averaging 133 cm in the Anamalais (31) and 177 cm in the Nilgiris (32). Nest trees tend to be tall trees of large girth (see Table 5 for detailed nest tree characteristics).
In tropical wet evergreen forest of the Anamalai Hills, they nest in tall evergreen forests (average canopy height 24 m), with nest trees located in sites that have higher tree density and denser undergrowth (31).
As the birds are secondary cavity nesters, they do not construct their nests, but instead use existing cavities that are formed mainly by wood rot. Prior to occupation, the adult pair visits the nest and may repair the cavity entrance or remove debris to clean the nest (DM, personal observations). The female enters the nest and using her bill seals the cavity opening with her droppings, forming a seal with a slit-like opening through which the male will feed her for nearly twelve weeks.
The nest cavity entrance is predominantly round, rarely oval. The interior dimensions of one nest examined in the Anamalai Hills was 25 cm wide by 36 cm deep. The cavity extended into the interior of an adjoining branch forming a "funk hole" into which the incubating female withdrew. The measurement along this axis was 63 cm. Cavity lacked any inner lining, except for some wood debris with some seeds (31). See Table 6 for detailed nest cavity parameters.
In the Nilgiris, 63% of 40 nest cavities were oriented towards the east (32). In the Anamalai Hills, a study of 27 nests in 1993-94 reported that 41% were oriented towards NE, 22% towards SW, and 22% towards SE (31). A later study of 59 nests from the Anamalai Hills, found more nests oriented towards NW and SE directions (P. Y. Pawar, D. Mudappa, and T. R. S. Raman, unpublished data). This suggests that there may not be specific choice of nest cavity orientation in the species and the orientation may simply reflect availability of cavities in different localities (31).
Maintenance or Reuse of Nest
When the female is confined to the nest cavity, she may eject debris and waste including eggshells through the cavity opening, and also constantly maintains the seal using her droppings (DM, personal observations).
The birds show high nest site fidelity with nest cavities often reused for many years. Of 27 nests located during a study in 1993-94, 10 nests were found to be active in 2018 (31, P. Y. Pawar, D. Mudappa, and T. R. S. Raman, unpublished data). Nest cavities may be abandoned in later years due to expansion or shrinkage of the cavity, predation, occupation by bees, treefall, and fire damage (32, 33, 20).
During the non-breeding season, nest cavities may be used by large brown flying squirrel (Petaurista phillipensis), Bengal monitor (Varanus bengalensis), and Malabar spiny dormouse (Platacanthomys lasiurus).
Average of 50 eggs was 41.8 mm by 30.3 mm (34).
Color and Surface Texture
The eggs are white with pitted shells.
Incubation begins soon after the female enters the nest, at the start of the nesting period in February. The mean nesting period was 86 days (SD = 2.7, n = 4 nests) in the tropical wet evergreen forest of the Anamalai Hills, of which observations at a focal nest indicated that the incubation phase was 40 days (24). According to another study of 5 nests, incubation period was 28 – 30 days out of an overall nesting period of 73 – 82 days (20).
Condition at Hatching
Hatchlings are altricial.
Growth and Development
In the Anamalai Hills, observations at a focal nest indicated a post-hatching phase of 46 days, following which the female and chick emerged from the nest together 86 days after the female entered the nest (24). Another study reported a nestling phase of 45-52 days, with the female in the nest for 64-71 days, during the 73-82 day nesting period (20). The chicks usually hatch around mid-March.
All brooding done by female.
When the female is confined in the tree cavity nest for approximately 86 days (including incubation and post-hatching phases), the male hornbill visits daily to deliver food at the nest. A study at a focal nest in the Anamalai Hills noted that the male makes about 1 to 2 visits per hour on average, with a peak in visitation shortly after the hatching. Time spent at the nest was slightly higher in the pre-hatching phase as more small fruits were delivered and each had to be individually regurgitated (24). While approaching the nest, the male does not approach directly, often perching on a nearby branch and looking around before flying to the nest.
Brood Parasitism by Other Species
Not brood parasitized.