Breeding Ecology of the Edible-nest Swiftlet Aerodramus
fuciphagus and the Glossy Swiftlet Collocalia esculenta in the
Andaman Islands, India
The intriguing biological feat of making a nest with its saliva is threatening the survival of the
edible-nest swiftlet. Ever since the16th century when bird’s nest became a delicacy in Chinese
cuisine and an important item in their pharmacy, edible nest swiftlets are found overexploited
all over. In the past two to three decades the production of the edible bird’s nests has reduced
drastically because of over-exploitation and uncontrolled harvesting that is directly affecting
the population of this cave-dwelling species. The high demand in the international markets has
put so much pressure that despite strict regulations on nest collection, the wild populations of
the edible-nest swiftlets is plummeting by as much as 80% to 90% and has reached local
extinction across some of their ranges.
India has four species of swiftlets: the Indian Edible-nest Swiftlet Aerodramus unicolor (Jerdon
1840), the Himalayan Swiftlet Aerodramus brevirostris (McLelland 1840), the Glossy Swiftlet
Collocalia esculenta (Beavan 1867) and the Edible-nest Swiftlet Aerodramus fuciphagus (Hume
1873). Edible-nest swiftlet, the producer of edible nests, is distributed only in the oriental region
of the world and the Andaman and Nicobar Islands of the Indian Territory. The collection of
these commercially valuable nests started in the Andaman and Nicobar Islands in the 18th
century. International demand led to widespread and uncontrolled nest collection in these
islands leading to a severe fall in population.
A programme to conserve the edible-nest swiftlet in the Andaman and Nicobar Islands
commenced in 1995, and is being implemented by the Department of Environment and Forests,
Andaman & Nicobar Islands (ANF) and Sálim Ali Centre for Ornithology and Natural History
(SACON) since 2001. The programme is implemented in 28 caves at Chalis-ek, Pattilevel,
North Andaman Island and one cave at Interview Islands Wildlife Sanctuary, Middle Andaman
Islands. These 29 caves hosting colonies of the edible-nest swiftlet are protected during the
breeding season between January and August. The species Aerodramus fuciphagus
inexpectatus (Hume 1873) was studied in its natural habitat as part of the programme. Though
data collection began in 2001, it was collected mainly between 2004 and 2007. As the glossy
swiftlet Collocalia esculenta affinis (Beavan 1867) of the island group has a significant role to
play in the ex-situ conservation of edible-nest swiftlet in urban areas, wild populations of this
species were initially studied along with the edible-nest swiftlet to know the ecology of these
species in their natural habitats.
The two sympatric species, i.e., the edible-nest swiftlet and the glossy swiftlet were studied for
their breeding ecology concerning their habitat requirements and the impact of protection on
the population of the edible-nest swiftlet in the Andaman and Nicobar Islands.
Nest-site characters, preference and the relationship with nesting success were studied to
understand the nest-site requirements of the edible-nest swiftlet. Results showed that the edible-
nest swiftlet and the glossy swiftlet are cave-dwelling trogloxenes and do not nest randomly
inside the caves. The ability to echolocate allows the edible-nest swiftlets to nest and roost in
the dark zones of the caves. The glossy swiftlet does not echolocate and therefore builds its
nests near cave openings in the dim-lit zones of the cave. The Edible-nest and glossy swiftlet
have shown their preference for rough and slightly rough-textured rocks, inwardly inclined
walls, with a presence or absence of supports and the different combinations of these
characteristics during nest-site selection. These preferred characteristics and their combinations
contribute substantially to nesting success among edible-nest swiftlet. Micrometeorological
parameters were studied inside the caves. The mean temperature showed a negative
relationship with nesting success, while relative humidity showed a positive relationship in the
case of edible-nest swiftlets. This information gives clear solutions to engineer better ex-situ
swiftlet houses for edible nest swiftlets.
Foraging habitat requirements were studied near the breeding colonies of the species at Chalis-
ek. The aerial and foraging behaviors and their occurrence in different habitats and
microhabitats helped to estimate the foraging habitat requirements of both species. Both these
exclusively aerial foraging species showed a noticeable difference in their foraging habitat
requirements near their breeding sites. The edible-nest swiftlets depend on forest canopy to a
great extent, whereas the glossy swiftlets forage in both forest and open land habitats. Edible-
nest swiftlets preferred heights above the canopy level and also close to the top of the canopy.
Glossy swiftlets were seen foraging close to the canopy top in forested areas and below canopy
levels in the loose vegetations along streamsides in the deforested open patched. The current
rate of deforestation can severely affect the populations of the edible-nest swiftlets, whereas
the glossy swiftlets are much better adapted to forest alterations.
Nests of both the species were visited daily to study their breeding seasonality and chronology.
The study shows that the edible-nest swiftlets in the Andaman and Nicobar Islands have a well-
marked breeding season with two broods from December to August, whereas, the glossy
swiftlets in the wild breed throughout the year and fledge almost four broods per year. The
breeding seasonality in the edible-nest swiftlet is linked with rainfall. Glossy swiftlets do not
show any relation with meteorological parameters. Edible-nest swiftlets use the only saliva as
the nest material whereas the glossy swiftlets use moss, twigs, grass, vegetation matter, and
others, glued together with their saliva. The behavioral study of the edible-nest swiftlets
showed that they copulate mostly on the nests and have a slightly longer incubation and
fledgling period as compared to the glossy swiftlets. Both the species have a typical clutch size
of two eggs with comparatively successful first clutch than the second. Detailed information
on the breeding biology of the species provides support for planning the fostering programme
and also to predict the hatching and fledging success of the edible-nest swiftlet eggs in the
glossy swiftlet nests. This information can be utilized for proper scheduling of cave protection
and nest harvest timings and to develop a protection system for in-situ conservation.
The continuous improvement in the population growth has proved that the strategy of
protecting the populations of edible-nest swiftlet in their natural habitat with the involvement
of motivated nest collectors is a successful method of conserving edible-nest swiftlets in the
Andaman and Nicobar Islands. However, a population decline of over 73% in the unprotected
caves and local extinction from more than 60% of the unprotected caves surveyed within a
decade is alarming, which calls for the expansion of the edible-nest swiftlet conservation
programme all over the islands arc to prevent the extinction of the species.
Since the species was included in the Scheduled-I of the Wildlife Protection Act, 1972 in
September 2003, the post-breeding harvest of the bird’s nests is not possible. As a result, the
protectors deputed at the cave mouths are getting demoralized. It is to be noted that the
protectors were nest collectors who worked for the protection of the colonies with an incentive
to harvest the nests at the end of the breeding season. Their de-motivation could hinder the
expansion of the in-situ conservation programme. It is imperative to consider the removal of
the species from the schedules and to ensure the survival of the species through sustainable
practices, local participation, and scientific management.