Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 March 2025 | 17(3): 26690–26696
ISSN 0974-7907 (Online)
| ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.9476.17.3.26690–26696
#9476 | Received 02
November 2024 | Final received 02 February 2025 | Finally accepted 26 February
2025
Assessment of nest
and nesting activities of White-bellied Heron Ardea
insignis Hume, 1878 (Aves: Ardeidae) in the
broad-leaved forests of northeastern India
Himadri Sekhar Mondal 1
& Gopinathan Maheswaran
2
1,2 Zoological Survey of
India, M-Block, New Alipore, Kolkata, West Bengal 700053, India.
1 Bombay Natural
History Society, Hornbill House, Shahid Bhagat Singh
Road, Mumbai, Maharashtra 400001, India.
1 himadri1510@gmail.com
(corresponding author), 2 gmaheswaran@yahoo.com
Editor: H. Byju,
Coimbatore, Tamil Nadu, India. Date of publication: 26 March 2025
(online & print)
Citation: Mondal, H.S. & G. Maheswaran (2025). Assessment of nest and nesting
activities of White-bellied Heron Ardea
insignis Hume, 1878 (Aves: Ardeidae) in the
broad-leaved forests of northeastern India. Journal of Threatened Taxa 17(3): 26690–26696. https://doi.org/10.11609/jott.9476.17.3.26690-26696
Copyright: © Mondal & Maheswaran 2025. Creative Commons
Attribution 4.0 International License. JoTT allows
unrestricted use, reproduction, and distribution of this article in any medium
by providing adequate credit to the author(s) and the source of publication.
Funding: This study was funded by the Science and Engineering Research Board (SERB)
of the Department of Science & Technology, Government of India with the
reference to file number SR/SO/AS-62/2012.
Competing interests: The authors declare no competing interests.
Author details: Himadri Sekhar Mondal completed his PhD on the behavioural studies of Critically Endangered White-bellied Heron Ardea insignis from the Pondicherry University in 2019. He has joined BNHS as scientist on 2018 and has worked on different projects since then. He is currently working on the birds and wetlands of the Sikkim Himalaya. Gopinathan Maheswaran is presently working as senior scientist in Zoological Survey of India’s HQ office at Kolkata mostly on the foraging behavior of long-legged wading birds. He is currently involved in another DST-sponsored project on White-bellied Heron in Namdapha Tiger Reserve of Arunachal Pradesh.
Author contributions: HSM involved in data collection, analyses, conceptualization and writing of this article. GM helped in writing of this article and also, involved in its correction and accrued the fund for this study.
Acknowledgements: We thank the director, Zoological Survey of India, Kolkata, for encouragement and support throughout the study and the Science and Engineering Research Board (SERB)
of the Department of Science & Technology, Government of India, for financial support of the study of White-bellied Heron in Namdapha Tiger Reserve through grant SR/SO/AS-62/2012 offered to the second author. We also thank the Department of Forests and Wildlife, Government of Arunachal Pradesh, for giving us permission to stay and study within the reserve for a large part of the year. Finally, we thank our four field assistants; without whose help this study could not have been possible in such a difficult terrain.
Abstract: The discovery of
White-bellied Heron Ardea insignis
nesting in India in 2014 was a significant record since it was the second
nesting report in India after one reported in Bhutan ‘dooars
(= Terai)’ below Darjeeling. White-bellied Herons are
known to build their nests in the riverine forests between 300 m and 1,500 m.
The majority of the nesting records are from Chir
Pine Pinus roxburghii forests of Bhutan. This
article highlights heron’s nest site selection and nesting activities in the
broadleaved forests in Arunachal Pradesh, India. During the study period
(2013–2017) in Namdapha Tiger Reserve, two active
nests of this species were recorded one in 2014 and another in 2015. Though
both the nests failed without producing any offspring, the findings, shed
crucial information, especially on how the herons select their nesting sites
and nest trees and the risks involved in the process. These findings will help implement
conservation actions especially while safeguarding the known nesting sites in
India.
Keywords: Arunachal Pradesh, behavioural ecology, Critically Endangered, eastern Indian
Almond, Hollock, Namdapha,
nest material trips, nesting tree.
INTRODUCTION
The White-bellied
Heron (WBH hereafter) is the only heron classified as ‘Critically Endangered’
by the IUCN Red List of Threatened Species (Maheswaran
et al. 2021a; BirdLife International 2024). It is a
resident in Bhutan, northeastern India and Myanmar with merely about 60
reported individuals (Price & Goodman 2015 Maheswaran
et al. 2021b). In India, it is mainly reported from Namdapha
Tiger Reserve (Mondal & Maheswaran 2022), Kamlang National Park and reserve forests in Walong area of Anjaw District,
Arunachal Pradesh (Reddy et al. 2021).
In Bhutan, the first
nest of WBH was reported in 2003 (Acharja 2019; Khandu et al. 2020); with 27 active nests identified by
2017 (Khandu et al. 2020). In India, Hume & Oates
(1890) reported the first nest of Ardea
insignis as a platform of sticks placed on the top of a large tree in an
inaccessible swampland southern of Darjeeling, in the Bhutan dooars (= terai). No photographic
evidence was available as it only mentioned that a large stick nest was placed
high upon a large tree in a swampy and inaccessible area. The breeding period
mentioned was during July–August. the present study documents two nests of WBH
from the Namdapha Tiger Reserve. This article will be
the first of its kind that will assess the nesting of this rare heron species
in India and aid in further research and future conservation action and
management plans.
MATERIALS AND METHODS
During the study
period (2013–2017), in Namdapha Tiger
Reserve (27.392–27.661 °N & 96.251–96.976 °E) (NTR hereafter) (Image 1),
all the activities of WBHs were monitored and recorded along with their nest
building activities. The studies focused on understanding how nest site/s were
selected and followed by the nest building activities.
Behavioural observation
Studies on
nest-building activities of WBH were conducted over two years (06–18 March 2014
and from 24 February 2015 to 10 May 2015). Nesting activities were observed for
a total of 39 days—eight days in 2014 and 31 days in 2015. The longest
continuous stretch of observation was from 24 February to 4 April 2015. During
this period, observations were made for 25 days with intervals of 1–2 days in
between. The continuous scan sampling method (Martin & Bateson 2007) was
used to record various nest-building activities of WBH from 0530 h to 1730 h.
Various behavioural activities of WBH were observed
during this period: courtship (making calls for its mate and greet their mates
when they come back to the nest), nest-material trips (when one of the pair
flew to bring nest material to the nest), foraging (catching fish at the
river). Observations were made from a distance of 300 m with a pair of 8 x 40
binoculars (Nikon) and a spotting scope (Nikon) and photographed with Nikon
D70S SLR camera and Sigma 500 mm telephoto lens. Hideouts constructed at a
distance of 100 to 150 m from the nest tree to observe behavioural
activities without disturbing the nesting. Locating the active nest of WBH is
merely a chance and can be found by following the adult bird from their
foraging sites to the roosting area, especially during breeding season. As soon
as WBH was spotted at its nest, or seen building the nest, the observation on
the individual/pair started and continued till the heron(s) disappeared from
the sight or flew away towards the Noa-Dehing River
for foraging or nest material collection. As WBHs do not have any distinctive
sexual dimorphism, identifying individual birds remained difficult.
Evaluation of the
nesting sites and nests
The tree species used
for nesting by WBH was identified using Chowdhery et
al. (1996). The height of the nesting tree and the height at which the herons
built their nests were measured using conventional methods of measuring a
smaller tree nearby, using rope and then extrapolating that with the nest tree
to arrive at the actual height. The diameter of the fallen nest was measured
with the help of a measuring tape. Coordinates and elevations of the respective
locations were recorded using Garmin GPS. Using Google Earth, the aerial
distance were measured between the nesting tree and
the regular foraging sites and human tracks and villages.
Data analysis
Nesting: Time spent
by WBH in nesting was calculated for each day. The entire observation period of
a day was divided into three categories:
Morning: 0530–0930 h.
Mid-day: 0930–1330 h.
Evening: 1330–1730 h.
The percentage time
spent by the pair in nest-building activities was calculated for different
times of the day.
Hours spent on nesting on a specific category
of time of the day X 100
––––––––––––––––––––––––––––––––––––––––––––
Total hours spent on nesting
Mean±SD of each of these
categories were calculated to understand during which time of the day the
species preferred to construct their nest.
Nest material trips
‘Nest material trips’
are the trips (flights) made by the adult nesting birds from their nesting tree
to the nearby trees or land and return to their nest with sticks in their bills
(Maheswaran & Rahmani
2005). These sticks or ‘nest materials’ are collected by the WBH, waiting in
the nest. Whenever the herons returned to the nest with nest materials in their
bills the time taken to make such trips was also recorded. At a time, WBHs were
seen collecting only one piece of nest material. Percentage (%) of nest
material trips and percentage (%) and Mean±SD value
of time spent on such trips were calculated for each category during different
times of the day and also for the years 2014 and 2015, separately.
RESULTS
Nesting sites: Two nests of WBH, one
each in 2014 and 2015, were located in different tree species (Table 1) that
were 2.69 km apart. Each year, one pair of WBH was spotted building the nest.
It could not be confirmed whether the same pair of WBH constructed both nests.
Certain features were common for both nesting sites.
Forest type: The forest type of
this area is categorized as the northern tropical evergreen forest or Assam
Valley tropical wet evergreen forest. Champion & Seth (1968) mentioned
three types of forests in NTR: (a)—northern tropical evergreen forest or Assam
Valley tropical wet evergreen forest (dominated by Dipterocarpus)
| (b)—northern Indian tropical moist deciduous forest (dominated by Terminalia)
| and (c)—miscellaneous forest (no single species dominance). In both years,
WBHs were seen building their nests only in the nearby riverine or fringes of
the forests but not much in the interiors.
Forest edge: The trees chosen to
build the nest were at the forest edge, between the open riverbed and the
interior dense forest. Distance of the nesting tree from their regular foraging
site was 663 m and 201 m in 2014 and 2015, respectively.
North-sided forest: WBHs were seen
almost regularly foraging in the Noa-Dehing River
that flows in an east-west direction at the 27-mi area of NTR. Both nests were
recorded at the north-sided forest of this area. Also, the north-sided forest
is less anthropogenically disturbed than the south-sided forest.
Nest Azimuth: In both years WBHs
were seen building their nest facing east that ensured better reception of
sunlight throughout the nesting period.
Human trails: The nearest human
track was on the other side of the Noa-Dehing River
(near south sided forest), more than 800 m away from the nest. The nearest
human settlement was far more interior in the forest (at least 1.5 km away from
the nesting site) (Table 1).
Nesting tree height: WBH selected 22–33 m
trees to build their nests although there were many tall trees in the vicinity.
Position of the nest
in the tree: WBH did not construct nests at the top of the nesting
tree but the nests were built at the middle, more specifically on the outer
branches (Images 2, 3, & 4).
Nesting activities
In 2014 and 2015, in
NTR, the courtship of WBH was observed starting from January onwards. In 2014,
WBH already started building their nest by the time we noticed them on their
nest for the first time (Image 2). On 24 February 2015, it was assumed that the
WBH pair was seen to assess the trees to select the nesting tree as they were
flying from one tree to the next and eventually settled for one, where they
removed a few branches and leaves with their bill to create some vacant
space to build their nest. From 26 February 2015 onwards, the pair started
nest material trips that lasted up to 21 March 2015. The number of nest
material trips gradually decreased towards the later phase of the nest-building
period. During this time, WBHs were also seen spending a considerable amount of
time on the nest without any nest material trips (Image 3). From 25 March 2015
onwards, at least one of the adult herons was seen in the nest throughout the
observation period, indicating that the female had laid the egg(s). No drastic
step like moving very close to the nest in the presence of the birds or
climbing up the nesting tree were undertaken to observe the activities of
adults and to look for eggs and chicks at any point in time ensuring zero
disturbance in their habitation and activities.
Nesting activities of
WBH were observed for a total of 93.74 h (17.67 h in 2014 and 76.07 h in 2015)
in 34 days (8 days in 2014 and 31 days in 2015). During this period, WBHs were
recorded completing 175 nest material trips (total duration – 17.8 h).
During the nesting
period (mainly at the beginning), WBHs were spotted less frequently at their
foraging site/s during morning hours as they were engaged in nest-building
activities (Table 2 & 3). The majority (90.85%) of the nest material trips
were also conducted in the morning (Table 3). These trips generally started
from 0630 hr and were at their peak at 0700–0800 h.
Each trip was 0.02 to 0.3 h long. The mean length of each nest material trip
was 0.10±0.06 (Mean±SD) hr. On four occasions, the
herons were seen returning to the nest without any nesting material (n = 1 in
2014 and n = 3 in 2015). Generally, the pair were seen to cease their
nest-building activities around 0830 h and both of them flew (generally one
after another) to their foraging site/s.
Fate of the
identified Nests
2014: The breeding
success of the 2014 nesting pair was not known because that study could not be
continued from mid-March 2014 onwards due to excessive rainfall and heavy
floods in the study area. The nest that WBH built in 2014, could be seen on the
same tree but found abandoned in 2015 (Image 4).
2015: On 13 May 2015,
it was found that the WBH nest amidst the boulders (almost dried stream) (Image
6). The maximum diameter of that nest was 141.8 cm. The fallen nest consists of
only dry branches or twigs of 50–110 cm in length (average length 83.46±15.60
cm; n = 24). One large portion of the broken eggshell (3.6 cm length) was also
found at the same site (Image 5), 28.2 m away from the fallen nest. It was
presumed that it was of WBH as we could not see any other nest nearby. The
outer colour of the recovered eggshell was light blue
with a white inner surface. No traces of yolk were present in the egg shells.
As permission to collect samples were not granted, the egg shells and the twigs
were left in place after being photographed. The reason why the nest had fallen
remains unclear.
During the remaining
study period (till January 2017) in the study area, we neither came across any
other nests nor any juveniles of WBH in NTR.
DISCUSSION
Larger herons are
generally known as colonial breeders (Kushlan &
Hancock 2005; Stier et al. 2017; Byju et al. 2024)
but WBH is a solitary breeder. In Bhutan, WBH were mainly known to nest in the Chir Pine Pinus roxburghii trees
(Acharja 2019; RSPN 2024). The study discovered that
WBHs also prefer broadleaved forests. In 2018, a similar record also from
Bhutan (Nesting trees Michelia champaca and Pterospermum
acerifolium; Khandu
et al. 2020). In 2021, two WBHs with their active nest were spotted in Walong (1,123 m), Anjaw District,
Arunachal Pradesh (Reddy et al. 2021), a habitat dominated by Chir Pine forests.
Nesting site
selection is extremely essential for the continual survival and reproduction of
the nesting bird species (Dyrcz et al. 1981; Nguyen
et al. 2003). Forest fires at the Chir Pine forest
nesting sites are quite frequent in Bhutan and Walong.
Whereas, the nesting sites in the broad-leaved forest are less likely to suffer
from forest fire (Khandu et al. 2020).
In NTR, WBHs selected
22–33 m trees to build their nests at the height of 18–25 m (Table 1), similar
to the height of the nests (18.3±7.4 m) in the trees in Bhutan (Acharja 2019).
For the majority of the
cases in Bhutan, WBH nests were at the top of the nesting tree (Acharja 2019). In NTR, WBH constructs their nests in the
middle, more specifically on the outer branches. Such a position ensures easy
entry and exit for a large bird-like WBH (wingspans approximately 2 m in
flight), better visibility of their feeding sites and potential threats or
disturbances nearby (Mondal & Maheswaran 2014).
The nearest human
track and human settlement were on the other side of the Noa-Dehing
River (near south-sided forest) (Table 1). Hence these nesting sites receive
less anthropogenic disturbances. This is very important for a shy species like
WBH (RSPN 2012; Acharja 2019) whose minimum tolerance
distance to human presence was roughly estimated to be 150 m in Bhutan (Acharja 2019). In NTR, the herons are more
shy and the tolerance distance to any human presence was around 200–300
m. WBH have been found to remain in their nests until any disturbance or threat
from closer distance particularly during their initial phase of nesting.
From the information
available on the WBH nesting sites in NTR, Bhutan (Acharja
2019) and Walong (Reddy et al. 2021), the following
possible inferences can be drawn.
They nest at the
riverine forest edges that are also close to their feeding grounds.
Furthermore, the vast open river gave herons a clear view of any approaching
threat.
They prefer to nest
in the north-sided forest maybe because it is less disturbed
and they can build east-facing nests that can potentially aid in the incubation
process by providing heat from direct exposure to the sun.
They tend to abandon
their older nests though this aspect needs to be studied further.
Both in India and
Bhutan, nesting of WBH usually begins from late February to early March
onwards. Herons generally build their nest during morning hours (Kushlan & Hancock 2005). The weather during morning
hours seems less stressful to birds and morning fog in this area can soften the
tree branches and make it easier for the WBH to break. Most likely it took
almost a month for the pair to prepare their nest for laying eggs. After laying
the eggs, they spent more time hatching or protecting the eggs/ chicks from
danger.
The diameter of the
fallen nest is similar to the nest diameter (1.5 m) of the large heron species,
as suggested by Kushlan & Hancock (2005). In
Bhutan, the diameter of the WBH nests was measured at around 87–120 cm (Acharja 2019). The larger diameter of the nest in NTR, can
be attributed to the loosening of twigs when the nest fell from 25 m height.
Like Great Blue
Heron, the broken egg shells found beneath the nesting tree might indicate the
possible result of hatching (Cottrille & Cottrille 1958). No live or dead chicks were found near the
spot in NTR. Acharja (2019) postulated that WBH
nesting in the broad-leaved forest can result in breeding failure particularly
because of predation. In Punatsangchhu, Bhutan,
numerous droppings of small frugivorous mammals and monkeys were found near the
unsuccessful nesting sites (Acharja 2019). No such
droppings were found at the fallen nest site in NTR.
Though the
observations on these two nests were anecdotal, their discovery in the riverine
habitat of the broad-leaved forest indicates the importance of conserving this
habitat not only to ensure future conservation of the breeding pairs within NTR
but also ensure long-term survival of the species in NTR (Mondal & Maheswaran 2022), particularly when this area is infamous
for illegal logging, hunting (Datta et al. 2008) and
fishing (Maheswaran 2007).
Table 1. Details of
the nesting trees of White-bellied Herons identified in Namdapha
Tiger Reserve.
|
Particulars |
First nesting tree
(2014) |
Second nesting tree
(2015) |
|
Common name |
East Indian Almond Terminalia myriocarpa (Van Heurck & Müll. Arg.) |
Hollong Dipterocarpus macrocarpus (Vesque) |
|
Local name |
Hollock |
Hollong |
|
Altitude |
426 m |
410 m |
|
Height of the
nesting tree |
22–27 m |
28–33 m |
|
Height of the nest
from the ground |
18 m |
25 m |
|
Distance from
nearest regular foraging site |
663 m |
201 m |
|
Distance from human
settlement or road |
1.55 km (nearest
village) 0.86 km (from the
nearest regular dirt track used by villagers) |
1.90 km (nearest
village) 1.36 km (from the
nearest regular dirt track used by villagers) |
Table 2. Time spent
by White-bellied Heron while nesting during different times of the day in Namdapha Tiger Reserve.
|
Observation |
Times of the day
(h) |
||
|
Morning |
Mid-day |
Evening |
|
|
2014 |
16.37 |
0.72 |
0.58 |
|
2015 |
45.08 |
16.40 |
14.58 |
|
Total |
61.45 |
17.12 |
15.17 |
|
Percentage (%) Mean±SD |
77.96±36.71 |
14.07±29.86 |
9.51±23.52 |
Table 3. Nest
material trips by White-bellied Heron during different times of the day in Namdapha Tiger Reserve.
|
Times of the day |
Number of nest
material trips |
Duration of nest
material trips |
|||
|
n |
% |
hr |
% |
||
|
Total |
Mean±SD |
||||
|
2014 |
54 |
30.86 |
6.48 |
0.12±0.06 |
36.42 |
|
2015 |
121 |
69.14 |
11.32 |
0.09±0.06 |
63.58 |
|
Morning |
159 |
90.85 |
16.87 |
0.11±0.06 |
94.75 |
|
Mid-day |
13 |
7.43 |
0.77 |
0.06±0.03 |
4.31 |
|
Evening |
3 |
1.72 |
0.17 |
0.06±0.04 |
0.94 |
|
Total |
175 |
100 |
1068 |
6.10±3.68 |
100 |
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