Journal of Threatened
Taxa | www.threatenedtaxa.org | 26 January 2025 | 17(1): 26341–26352
ISSN 0974-7907 (Online)
| ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.8661.17.1.26341-26352
#8661 | Received 02
August 2023 | Final received 14 October 2024 | Finally accepted 17 December
2024
Dietary composition of Black-necked Crane Grus
nigricollis Przewalski,
1876 (Aves: Gruiformes: Gruidae)
in its winter habitat: insights from fecal analysis in Bumdeling,
Trashiyangtse, Bhutan
Jigme Wangchuk 1,
Ugyen Tenzin 2, Tsethup
Tshering 3, Karma Wangdi
4, Sangay Drukpa 5, Tshering Chophel 6, Ugyen Wangmo 7, Jigme Tshering 8 & Sherub
9
1,2,3,4,9 Ugyen Wangchuck Institute for
Forest Research and Training, Department of Forests and Park Services, Lamai Goenpa, Bumthang
34005, Bhutan.
5,6,7 Bumdeling Wildlife Sanctuary, Department of Forests and
Park Services, Bumdeling Trashiyangtse
46001, Bhutan.
8 Royal Society for
Protection of Nature, Civil Society Organization, Thimphu
11001, Bhutan.
1 jickmew@gmail.com (corresponding
author), 2 utenzin@uwice.gov.bt, 3 ttshering@uwice.gov.bt,
4 kwangdi@uwice.gov.bt, 5 drukpa6060@gmail.com, 6 tsherichobhel@gmail.com,
7 ugyenwang2017@gmail.com, 8 jtshering@rspnbhutan.org, 9
sherub@uwice.gov.bt
Editor: Carol Inskipp,
Bishop Auckland Co., Durham, UK. Date of publication: 26 January 2025
(online & print)
Citation: Wangchuk, J., U. Tenzin, T. Tshering, K. Wangdi, S. Drukpa, T. Chophel, U.
Wangmo, J. Tshering & Sherub (2025).
Dietary composition of Black-necked Crane Grus nigricollis
Przewalski, 1876 (Aves: Gruiformes:
Gruidae) in its winter habitat: insights from fecal analysis in Bumdeling, Trashiyangtse, Bhutan. Journal
of Threatened Taxa 17(1): 26341–26352. https://doi.org/10.11609/jott.8661.17.1.26341-26352
Copyright: © Wangchuk et al. 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 research grants was supported by International Crane Foundation, USA and Royal Society for Protection of Nature, Bhutan.
Competing interests: The authors declare no competing interests.
Author details: Jigme Wangchuk, based at UWIFoRT, focuses on freshwater ecology, climate modeling, and ecosystem services. Ugyen Tenzin, a forest ranger at UWIFoRT, has a keen interest in birds, and mammals. Karma Wangdi, a forest ranger and Lepidopterist at UWIFoRT, conducts biodiversity surveys and catalogs Bhutan’s butterflies and moths. Tsethup Tshering, also a forest ranger at UWIFoRT, specializes in botany. Sangay Drukpa works as the senior forest ranger at Bumdeling Wildlife Sanctuary in Trashiyangtse, Bhutan. Tshering Chophel works as a forest ranger at Bumdeling Wildlife Sanctuary. Ugyen Wangmo, formerly a forester at Bumdeling Wildlife
Sanctuary, is currently pursuing further studies in Perth, Australia. Jigme Tshering, the national coordinator for Black-necked Crane conservation at RSPN, focuses on research and habitat protection for Black-necked Cranes. Dr. Sherub, an ornithologist and head of the Center for Conservation at UWIFoRT, has diverse research interests centered on understanding and measuring the biodiversity rhythms of life forms.
Author contribuions: JIGME WANGCHUK designed, gathered and analyzed the data, and prepared and reviewed the manuscript; UGYEN TENZIN collected, processed, and analyzed fecal samples in the laboratory; KARMA WANGDI gathered data; TSHETHUP TSHERING collected data, identified fecal fragments and reviewed manuscript; SANGAY DRUKPA, TSHERING CHOPHEL, and UGYEN WANGMO gathered the field data. JIGME TSHEING planned the study, secured funding, and conducted the internal review. DR. SHERUB planned, designed, collected fecal samples, conducted the internal review, and analyzed results. He played a pivotal role in providing the overall supervision for the achievement of this study. All authors contributed to finalizing the manuscript.
Acknowledgements: We are grateful to the management of Bumdeling Wildlife Sanctuary for their assistance in field data collection and logistical support. We thank the International Crane Foundation USA
and the Royal Society for Protection of Nature Bhutan for financial assistance. We also express our gratitude to the management of the Ugyen Wangchuck Institute for Forest Research and Training, Department of Forests and Park Services for their continued guidance and support, and to the Royal Government of Bhutan. We also acknowledge the RSPN for making this article available to all by sponsoring payment of the journal’s article publication fee.
Abstract: Gaining comprehensive
insights into the dietary habits and food preferences of the Black-necked Crane
(BNC) is crucial for developing effective conservation plans to safeguard this
globally near-threatened species. The choice of habitats by these birds is
primarily influenced by the availability of diverse food sources and overall
environmental security. This study was conducted in 2019–2020 in Bumdeling, one of three wintering sites for BNC in Bhutan.
It was prompted by concerns over a declining crane population, largely due to
habitat alteration that threatens food sources. This study aimed to examine the
dietary preferences of cranes by collecting and analyzing fecal samples from
foraging and roosting sites. Results revealed that paddy-fields were the primary
foraging areas. The presence of domestic grains after harvest, herbaceous
plants, and invertebrates are crucial components of the food structure of
cranes. Fecal samples contained 79 species from domestic crops, herbaceous
plants, and invertebrates. Fecal dry weight exhibited significant differences
from December to February compared to March, suggesting a decline in rice
intake and an increase in invertebrate consumption, resulting in lower fecal
weight. These results also showed that as the months progress rice decreases
with a shift to a protein-rich diet of invertebrates before cranes migrate back
to their summer grounds. Traces of plastics were found in feces from all
feeding sites, highlighting the need for better waste management. Changes in agricultural
practices have had significant impacts on the availability of food sources for
cranes in Bumdeling. Collaboration among
conservationists, local government, and communities is recommended to enhance
winter habitats and provide food supplements when rice supplies start to
diminish.
Keywords: Changing
agricultural practices, conservation strategy, declining crane population,
fecal dry weight, foraging and roosting behaviour,
herbaceous plant, paddy-fields, protein-rich diet, winter habitat.
Black-necked Crane (BNC) Grus nigricollis is a migratory species in the Central Asian
Flyway (CAF) that prefers high-elevation habitats for beeding
in summer and low-elevation areas for foraging in winter (Image 1). The largest
population occurs at the Tibetan-Qinghai Plateau in western China (Lhendup & Webb 2009; Dong et al. 2016), and a small
population occurs in Ladakh in India. During winter,
cranes typically migrate to a lower altitudes of 2,000–3,000 m (Harris & Mirande 2013), including Qinghai-Tibet and Yunnan-Guizhou
Plateaus in China, Arunachal Pradesh in northeastern
India, and Bhutan (BirdLife International 2020).
Their wintering habitats are mainly attributed to food availability and favorable climatic conditions. BNC is a globally ‘Near
Threatened’ species (BirdLife International 2024),
listed on CITES Appendices I and II. Its habitats continue to accrue
significant destruction (Li & Li 2012) and access to food sources continues
to reduce due to anthropogenic activities (Dong et al. 2016). The knowledge
about dietary habits, food preferences, and choice of habitats is important
evidence that will help devise conservation plans for the management of this
species effectively (Dong et al. 2016).
Bhutan has three main areas where the BNC
winters: Phobjikha in the west, Bumdeling
in the east, and Bumthang in the center
(Lhendup & Webb 2009; Namgay
& Wangchuk 2016). In these wintering grounds, BNC typically feed on
domestic crops like paddy, wheat, barley, buckwheat, potatoes, turnips, and
cereals where conventional agriculture is practiced by local communities,
however, elsewhere outside Bhutan grassland constitutes primary foraging areas
(Bishop et al. 1998; Dong et al. 2016). Birds feed on herbaceous plants,
especially the soft shoots found on roots, dwarf bamboo, tubers, and seeds, and
also on invertebrates such as snails, and earthworms, which are crucial for
their survival and health (Dong et al. 2016). They roost in shallow water, on
riverbanks, or in small ponds. The population is threatened by significant
changes in agricultural practices, industrial development, climate change,
habitat loss (Lhendup & Webb 2009; Namgay & Wangchuk 2016), and predation (Choki et al. 2011). The world population totals over 10,000
birds (Li 2014). Bhutan hosts more than 600 individuals annually during the
winter season between October and March
(Phuntsho & Tshering
2014). The BNC population in Bumdeling declined
steadily between 1980–2020 while it increased in Phobjikha
(Namgay & Wangchuk 2016; BNC 2021). If this trend
persists, the BNC may gradually abandon Bumdeling as
a wintering area as there were few instances reported in the distant past from Samtengang, Tshokana, Gongkhar (Lhendup & Webb
2009), Gaytsa, and Rodhungthang
(Namgay & Wangchuk 2016). The decrease in BNC numbers
can be attributed to both anthropogenic activities, such as infrastructure
development, and a series of natural events such as flash floods in Bumdeling in 1999, 2003, 2005, and 2007 (NCHM 2018), which
have disrupted their feeding and roosting grounds. On the other hand, it is
likely that the cultivation of winter crops in recent years after the rice
harvest has reduced the availability of critical foraging and roosting areas
which may have resulted in fewer BNCs visiting the sites.
The BNC plays a vital role in wetland
ecosystems by regulating the population of invertebrates at cascading trophic
levels. Culturally, these birds are considered sacred and believed to bring
blessings, which helps to protect their habitats. Conservation efforts, including
the designation of RAMSAR sites, habitat restoration, research on migration and
habitat preferences, and the integration of community agricultural practices
are being implemented. However, there is a lack of study on the dietary habits
of BNC during winter months at their foraging and roosting sites. This study
aims to address this gap by analyzing the dietary
composition using fecal samples of BNC from their
wintering grounds. By determining dietary needs and preferred food types, these
findings are expected to enhance understanding of their habitat interactions
and contribute to the development of long-term conservation plans (Dong et al.
2016) in Bhutan.
The study was conducted in Bumdeling Wildlife
Sanctuary (BWS) which falls within the northeastern
part of Trashiyangtse District, Bhutan. The Sanctuary
covers an area of 1,545 km2 encompassing parts of the Lhuntse, Trashiyangtse, and Mongar districts (Figure 1). It shares international
borders with the Tibetan region of China in the north and India in the
north-east. Our study area is limited to Trashiyangtse,
where the site is used as the wintering grounds by BNC. The sites include seven
crane foraging areas: Bayling, Baychen,
Batsemang, Gilingbo, Maidung, Tshaling, and Yangteng, and one roosting area: Dewalingjuk,
scattered along Bumdeling valley. The study area has
an altitudinal range of 1,785–1,921 m.
The mean temperature varies 15–25 0C. The annual rainfall
received in the area measures 2,000–3,000 mm. The study area covered all the
foraging and roosting sites used by the BNC in the locality. The foraging site
is located on farmland, where the main food crops grown by the
local communities are rice,
maize, millet, potatoes, and chillies. The roosting area consists of a shallow
braided river with several pools and grasslands.
Local forest officials and resident
communities were consulted to locate BNC annual foraging sites before starting
fieldwork. Seven foraging sites and one roosting site were identified for fecal sample collection. Consultation of local people,
observation, and involvement of local forest officials were key to site
selection, and the transect method was employed for collecting fecal samples from the foraging and roosting sites.
We collected 350 and 40 fecal
samples from the foraging and roosting sites, respectively. A transect walk was
conducted from December 2019 to March 2020. BNCs start to arrive in their
winter habitats by the end of November and leave for their summer habitats by
March each year. The first 10 fresh fecal samples
(intact) were collected from seven foraging and one roosting site. The fecal samples were sun-dried and wrapped in paper, and
transported to the laboratory in zip-lock bags. While collecting, safety gear
such as masks, hand gloves, and sanitizer were used to avoid fecal contamination and transfer of avian zoonotic
diseases. At each collection site, a quadrat measuring 1 m2 was laid
on where the feces were observed. Firstly, at the foraging
sites, surface-dwelling invertebrates were identified and counted, followed by
herbs enumeration within the plot. Those unidentified invertebrates’ specimens
were collected and later identified in the laboratory. Secondly, within a 1 m2
quadrat, a 10 cm2 plot with a depth of 10 cm was dug and the
invertebrates were identified and counted. Thirdly, at the roosting sites,
freshwater invertebrate samples from the pools, runs, and riffles were
collected using a kick net measuring 30 X 30 cm with a mesh size of 500 μm, and taxa were recorded.
Fecal analysis
Fecal sample analysis was carried out in the laboratory. Samples were
oven-dried for three hours at 60oC to eliminate moisture content and
avoid fungal growth. We measured the dry sample weight of all the fecal samples using a digital weighing scale and then
stored them at room temperature. Samples to be analyzed
were put in petri dishes and soaked in water overnight, and the next morning,
the contents were gently stirred to separate the plant fiber
and invertebrate components. The supernatant of the fecal
mixture was decanted into other petri dishes as invertebrate components
remained afloat, and heavier invertebrate parts were also hand-picked with
forceps. This method was adopted from Ralph et al. (1985) and Moreby (1988). The samples were repeatedly diluted and
decanted until the undigested fecal materials (fibers, seeds, husk, invertebrate parts) were thoroughly
cleaned and became identifiable under a microscope. The parts of undigested fiber and exoskeleton were placed on a glass slide and
examined using a microscope,
photographed, and identified. For the identification of undigested plant fiber, the method was adapted from Fengshan
et al. (1997) and
Liu et al. (2014), while for the identification of the exoskeleton of
invertebrates, we used established methods by Moreby
(1988), Ralph et al. (1985), and Liu et al. (2019). Depending on the size of
the undigested fecal fragments, identifications
were made to their taxonomic order, family, and species. The taxa names identified from fecal
fragments, quadrat sampling, and kick net sampling were validated and confirmed
by a national botanist and an entomologist. Soft-bodied organisms that may have
been fully digested were beyond the scope of our study, however, those observed
were included in our checklist.
To analyze the
dietary compositions from fecal samples, both
descriptive and inferential statistics were employed. For descriptive analysis,
we calculated the percent composition of different diet components, including
herbaceous plants, invertebrates, and domestic crops. For inferential analysis,
we used Kruskal-Wallis tests in R software to compare diet composition and fecal dry weight across various months and sites. To
compare diet composition and fecal dry weight between
roosting and foraging sites, we applied the Mann-Whitney U test (also known as
the Wilcoxon Rank Sum test). Given the non-normality of the data and unequal
group size, we used a non-parametric effect size measure Cliff’s delta to
compare fecal weight data between March (Group 1) and
each of the other months (December, January, February) treating each as group 2
in separate comparisons. We calculated Cliff’s delta (1993) using the equation:
δ = (D-U)/(n1 * n2). In this D is
the number of instances where a score from group 1 is greater than a score from
group 2, U is the number of scores from group 1 that are smaller than group 2,
and n1 and n2 are the number of observations in respective groups. The values
of 1 are given when a score from group 1 is greater than group 2, -1 when it is
smaller, and 0 when they are equal.
A total of 3014 fragments of ingested
materials were counted from 390 fecal samples
constituting 79 different types of dietary sources, mainly herbaceous plants
(41), followed by invertebrates (30), and domestic crops (4) respectively,
apart from small traces of plastics, fine pebbles (2–4 mm diameter), feathers
of birds, and fish scales were also evident in the fecal
samples (Table 1). However, in terms of composition, rice constitutes the
highest food source. This is certainly obvious as the remains of rice grains
are readily available in the farmland after the harvest. The results show that
domestic crops, herbaceous plants, and invertebrates constituted the main
dietary structure of the BNC. Domestic crops comprised the highest proportion
(70%) of the diet, followed by herbaceous plants (14%) and invertebrates (13%).
About 1% constitutes other diatary components such as
bird feathers, fish, plastics, and pebbles (Figure 2). The occurrences of
plastic waste, pebbles, and bird feathers were circumstantial, however, plastic
traces were present at almost all the feeding sites.
The main diet of BNC during the wintering
months appeared to be rice Oryza sativa, followed by herbaceous plants
and invertebrates. Data on diet composition in winter from December 2019 to
March 2020 showed insignificant differences in the Kruskal-Wallis rank sum
test; H = 1.269 (3), p = 0.05. The composition of diet content appears
to have a similar pattern throughout the months. The diet composition exhibited
no variation across different sites; H = 11.337 (7), p = 0.124. This showed
that all sites had similar composition of dietary sources chiefly rice grains
from paddy land. The top five food sources constitute Oryza sativa,
invertebrates, Schoenoplectiella juncoides, Potamogeton
nodosus, and Persicaria
perfoliata (Figure 2). Oryza sativa is an
essential dietary source followed by invertebrates which are attributed to the
higher number of fragments in feces samples. However,
it should be noted that most fragments which were not identifiable due to ingestion
were grouped together.
Dietary sources in roosting and foraging
sites are likely to have differences, the former being in the braided river and
island, and the latter in cultivated paddy-fields. Our in-depth analysis showed
that roosting sites had species that were not present in other sites. This is
primarily attributed to the composition of aquatic plants (Cladophora
sp. Dicranum viride,
Digitaria sanguinalis, Marsupella emarginata, Eriochloa villosa, Seleginella sp, and Urochloa ramosa)
and freshwater invertebrates (Aeshnidae, Athericidae, fish, Hydropsychidae,
Hydroptilidae, and Scirtidae)
which were observed only from the roosting sites. On the other hand,
foraging sites had the highest species composition and richness, possibly
because these sites comprised seven localities (Figure 3). To understand the
difference between the roosting sites (Dewalingjuk)
and the foraging sites, a Wilcoxon rank sum test revealed significant
differences in two of the seven site pairs; Batsemang
vs Roost, W = 2491.5, p = 0.016, δ = 0.05 and Tshaling
vs Roost site, W = 2397, p = 0.001, δ = 0.10. The other five pairs had no
significant differences; Roost site vs Maidung, W =
2736, p = 0.150; Bayling vs Roost site, W = 2999.5, p
= 0.651; Choetenkora vs Roost site, W = 2889.5, p =
0.390; Gilingbo vs Roost site, W = 2937.5, p = 0.491
and Roost site vs Yangteng, W = 2720.5, p = 0.132.
Cliff’s delta effect size (≤ 0.1) in the significant comparisons suggests that
the difference between the two groups was small.
Monthly variation of food
All 390 samples showed the presence of
herbaceous plants when pooled with domestic crops and plants. Undigested
materials from invertebrates were found in 281 samples, while 17 samples
contained traces of plastics, pebbles (13), feathers of birds (2), and fishes
(2). Species richness varied slightly over the four months, with December 2019
having the highest number of species. However, there was a steady decline in
the following month before increasing in March 2020 (Figure 4). The cranes had
access to more food sources at the time of their arrival in December, while
access to food resources declined in the following months after they fed on
them. Before migrating, the crane prefers invertebrates to store more energy
for their long flight to their summer grounds. The Poaceae
family was the most dominant species among the herbaceous plants, while Coleoptera was the most abundant food constituent in the
invertebrate group. Overall, species richness slightly fluctuates over the four
months, with herbaceous plant species decreasing and invertebrate species
increasing.
Dry weight of feces and rice grains across
different months
Of the 390 samples collected, 311 contained Oryza
sativa which is the primary food source for the BNC. An in-depth analysis
was conducted to determine the weight of undigested rice remains, including
husk, stem, and seeds, and it was found that the fecal
weight decreased over the months (Figure 5). In December, when BNC arrived at
their wintering grounds, there was a large amount of rice residuals (~14 g)
that had been harvested a month earlier. Over the following months, the
availability of rice grains gradually decreased, reaching a low point (~6 g)
just before the cranes left for their summer habitat. The decrease in rice
intake was probably compensated by an increase in the consumption of
invertebrates.
The dry fecal
weight corroborates the food availability and access for BNC. The weight of BNC
feces was highest in December, then gradually
decreased from January to February, with a sharp drop in March, indicating
reduced food availability due to repeated foraging in the area (Figure 6). The
mean dry weight per dropping of the BNC is 2.70 ± 1.06 g and they gain more
energy by feeding on invertebrates before flying back to their summer habitat.
The Kruskal-Wallis rank sum test revealed that dry weight data from December
2019 to March 2020 had significant differences among the months H = 34.657 (3),
p = 0.001. To determine which specific months had contributed to differences in
dry weight, a post-hoc test was performed. The months of December 2019, January
2020, and February 2020, when compared to March 2020, exhibited significant
differences based on the Wilcoxon rank sum test. These significance pairs were
evaluated to understand the magnitudes and strength of effect size between
independent paired months for March 2020 vs December 2019, W = 4612.5, p =
0.001, δ = 0.42; March 2020 vs January 2020, W = 4427.5, p = 0.001, δ = 0.43;
and March 2020 vs February 2020, W = 3837, p = 0.001, δ = 0.32. The main
observed differences with all three comparisons have positive data values
indicating second months (December 2019, January 2020, and February 2020) have
higher values than the first group (March 2020) respectively. However, the
effect sizes are relatively small (0.3–0.4). This can be attributed to the fecal dry weight in March 2020, with an increased intake of
invertebrates, which have higher protein content and constitute less
indigestible material compared to plant matter. Conversely, for the other
months, no significant differences were exhibited December 2019 vs January
2020, W = 3384.5, p = 0.052; December 2019 vs February 2020, W = 3514.5, p =
0.061, January 2020 vs February 2020, W = 3357, p = 0.20. These results were
largely due to the crane’s higher preference for herbaceous plants and lower
intake of invertebrate diet during these months consistent with the earlier
results.
In this study, the diet of BNC comprises 44
plant species, 31 invertebrate species, and four other food sources. Of the
combined 87 herbaceous plant species reported elsewhere in the
cranes-inhabiting regions by various authors Fengshang
et al. (1997) (48 species), De-jun et al. 2011 (5
species), and Lui et al. 2014 (43 species); and Plantago sp., Trifolium
sp., Poa annua,
Polygonum sp., Epilobium sp., Carex sp., Eriochloa
villosa, Juncus
effusus, Potamogeton
sp. Hydrilla verticillata, and Polygonatum sp. were also found in the feces samples of BNC from the present study. These species
are largely grown on the edge of the terraces and are occasionally found
growing along with the Oryza sativa. The primary diet of the BNC in the Bumdeling consisted of domestic crops, particularly Oryza
sativa. The high food quantity and density of paddy seeds in the farmland,
where residues are left after the harvest is the main reason why the cranes
have established their wintering grounds in this locality.
Several studies have documented that the diet
of cranes consists of fish, young birds, clams, shrimps, amphibians, molluscs,
and invertebrates (Chacko 1992; Han 1995, Li et al. 1997; Li & Li 2005; Liu
et al. 2014a,b, 2019). In this study, we report one fish species and two other
molluscs (Deroceras sp. and Orientogalba ollula).
The roosting sites characterized by shallow water provide the best habitat for
cranes to feed on fish. The slightly marshy wetlands left after the harvest of
paddy-fields support molluscs which
is a food source for cranes in the locality.
The invertebrate taxa consumed by the BNC,
identified at various taxonomic levels, include Coleoptera,
Hymenoptera, Diptera, Lepidoptera, and Araneae (Di-jun et al. 2011; Liu
et al. 2019), along with specific species such as Chorthippus
hsiai and Geotrupes
sp. (Wu 2007). In our study, we report several invertebrates identified down to
the lowest possible taxa levels, from terrestrial and freshwater systems that
were limited in previous studies. The fecal analysis
revealed the presence of 16 freshwater and 15 terrestrial invertebrate species.
Taxa such as Lumbriculidae, Tipulidae,
Athericide, and Diplonychus
sp. are soft-bodied and were recorded through field observations. In contrast,
others, largely comprising Coleopterans (Liu et al. 2019), were discovered from
the crane feces. Undigested fragments that were not
identifiable were grouped under invertebrates, which may constitute multiple
species. Although Coleopterans appear to be a supplementary food source for
BNC, they form an important food source after herbaceous plants. Fragments of Hesperocorixa interrupta
and Rhantus sp. were quite common compared
to other species. However, this list is underestimated, as many digested soft tissues were difficult to
examine and could not be accounted for. Although feces
provide an easy method for analyzing diet, completely
digested soft-bodied fragments and smaller indigestible particles make
identification more challenging. This highlights the need for future studies to
incorporate eDNA methods to improve accuracy.
The main factors that determine the arrival
and departure of cranes are influenced by the availability of food in the
farmland after the harvest. In December, just after the harvest, droppings of
paddy grains are most abundant and gradually decrease in the following months.
Animal matter, including protein- and fat-rich invertebrates from soil and
freshwater habitats (Liu et al. 2014a), is crucial for cranes, with higher
intake observed before migration to their summer grounds. Over the years, the
gradual decline in visiting BNC in the localities may be attributed to the
decrease in foraging areas, as nearby open spaces, including some agricultural
land, have been colonized by vegetation. Additionally, food availability has
decreased as the land used for rice production has been cultivated following
the paddy harvest, resulting in a reduction of the food supply. Studies
conducted elsewhere have shown that BNC forages in meadow habitats are rich in
calcareous food resources. Grazing effects in the meadows provide a wide range
of food for invertebrates, which are the main food source for BNC (Horgan
2002). However, in our study area, a foraging area solely consists of
paddy-fields, where cranes depend on the dropping of a variety of rice grains.
Occasional foraging has also been observed in the farmlands of localities where
communities grow food grains such as Eleusine
coracana.
Several challenges are causing degradation of
habitat for BNC, with issues emerging such as the discovery of plastics in the feces of BNC from the study area. Different ingested
plastic colors, such as white, green, and blue, were
evident in the feces. Plastics, though present in
small traces (<1%), were detected in feces across
all sites and throughout the study months. Such evidence is likely to affect
the health of the cranes and the surrounding environment in the long run. This
highlights the need for decision-makers to develop effective habitat management
and conservation strategies to address the increasing waste in crane foraging
areas.
Conclusions
We found that the Black-necked Crane prefers
cultivated land near human settlements, which provides them with easy access to
grains left on the ground after harvest. Their preferred winter foraging
habitat is closely tied to the local rice cultivation, which is crucial for
crane survival. Future changes in cropping patterns for rice cultivation may
impact crane wintering habitats. Localized rice
cultivars that yield more paddy seeds and drop a sufficient quantity of
seeds to support cranes must be prioritized. The crane spends the night in
shallow streams, ponds, and marshy areas, separated from the rest of the
localities, allowing them to remain secure from predators, which is important
for their safety. The fate of the crane population is intertwined with human
activities and their continued existence of wintering habitats in the study
area depends on agricultural practices. Changing farming practices and
colonization of foraging areas by trees would be a challenge for crane habitats
in the future. We recommend the collaboration of conservationists,
agriculturalists, and local communities to develop a suitable strategy that can
enhance the winter habitats of the BNC and supplement food gains for the cranes
when their rice supplies start to diminish.
Table 1. The
percentage composition of species in the dietary intake and the remnants of
identical parts present in the Black-necked Crane’s fecal samples.
|
|
Family |
Species |
Part of organ |
Frequency of
fragments |
Percentage |
|
Herbaceous plants |
|||||
|
1 |
Adoxaceae |
Viburnum sp. |
Leaf |
1 |
0.033 |
|
2 |
Asteraceae |
Chromolaena corymbosa |
Seed pod |
3 |
0.100 |
|
3 |
Asteraceae |
Bidens tripartita |
Seed |
9 |
0.299 |
|
4 |
Brassicaceae |
Cardamine hirsuta |
Leaves, stem |
3 |
0.100 |
|
5 |
Ceratophyllaceae |
Ceratophyllum demersum |
Needle leaves with
stem |
1 |
0.033 |
|
6 |
Cladophoraceae |
Cladophora sp. |
Undigested
filaments of algae |
16 |
0.531 |
|
7 |
Commelinaceae |
Commelina sp. |
Whole plant, leaf,
stem |
4 |
0.133 |
|
8 |
Cyperaceae |
Carex sp. |
Flower, seed, seed
pod |
23 |
0.763 |
|
9 |
Cyperaceae |
Schoenoplectiella juncoides |
Seed |
94 |
3.119 |
|
10 |
Dicranaceae |
Dicranum viride |
Leaf |
2 |
0.066 |
|
11 |
Equisetidae |
Equisetum sp. |
Stem |
3 |
0.100 |
|
12 |
Eriocaulaceae |
Eriocaulon nepalense |
Petal |
27 |
0.896 |
|
13 |
Fabaceae |
Trifolium hybridum |
Seed |
7 |
0.232 |
|
14 |
Funariaceae |
Funaria hygrometrica |
Seed and leaves |
10 |
0.332 |
|
15 |
Gymnomitriaceae |
Marsupella emarginata |
Leaf |
2 |
0.066 |
|
16 |
Hydrocharitaceae |
Elodea densa |
Leaf |
7 |
0.232 |
|
17 |
Hydrocharitaceae |
Hydrilla verticillata |
Leaf |
6 |
0.199 |
|
18 |
Juncaceae |
Juncus effusus |
Naked seed |
4 |
0.133 |
|
19 |
Lamiaceae |
Pogostemon stellatus |
Leaf, stem |
9 |
0.299 |
|
20 |
Lamiaceae |
Pogostemon erectus |
Leaf |
2 |
0.066 |
|
21 |
Lythraceae |
Rotala cordata |
Twigs, leaves, stem |
13 |
0.431 |
|
22 |
Lythraceae |
Rotala indica |
Flower, twig |
18 |
0.597 |
|
23 |
Nostocaceae |
Nostoc sp. |
Alike jelly fungus |
1 |
0.033 |
|
24 |
Plantaginaceae |
Plantago asiatica |
Leaf |
2 |
0.066 |
|
25 |
Poaceae |
Alopecurus aequalis |
Seed pod |
2 |
0.066 |
|
26 |
Poaceae |
Poa annua |
Seed with cover |
5 |
0.166 |
|
27 |
Poaceae |
Poa pratensis |
Seed |
17 |
0.564 |
|
28 |
Poaceae |
Setaria italica |
Seed, seed pod |
12 |
0.398 |
|
29 |
Poaceae |
Panicum sp. |
Seed pod, seed |
5 |
0.166 |
|
30 |
Poaceae |
Eriochloa villosa |
Seed |
1 |
0.033 |
|
31 |
Poaceae |
Digitaria sanguinalis |
Seed |
5 |
0.166 |
|
32 |
Poaceae |
Urochloa ramosa |
Seed with case |
1 |
0.033 |
|
33 |
Polygonaceae |
Polygonatum aviculare |
Sheath |
12 |
0.398 |
|
34 |
Polygonaceae |
Persicaria perfoliata |
Stem with spike |
32 |
1.062 |
|
35 |
Potamogetonaceae |
Potamogeton nodosus |
Leaf |
77 |
2.555 |
|
36 |
Araliaceae |
Hydrocotyle sibthorpioides |
Leaf |
6 |
0.199 |
|
37 |
Selaginellaceae |
Selaginella sp. |
Stem and leaf |
1 |
0.033 |
|
38 |
Xyridaceae |
Xyris capensis |
Awn |
1 |
0.033 |
|
39 |
Xyridaceae |
Xyris sp. |
Seed, seedpod,
flower |
7 |
0.232 |
|
40 |
Zygnemataceae (Algae) |
Spirogyra sp. |
Leaf |
2 |
0.066 |
|
|
Domestic crop |
|
|||
|
41 |
Amaranthaceae |
Amaranthus hybridus |
Seed |
5 |
0.166 |
|
42 |
Poaceae |
Oryza sativa |
Husk, seed, sheath,
leaf, stem digested remains |
2182 |
72.395 |
|
43 |
Poaceae |
Triticum aestivum |
Seed |
1 |
0.033 |
|
44 |
Poaceae |
Eleusine coracana |
Seed |
13 |
0.431 |
|
|
Terrestrial
invertebrates |
|
|||
|
45 |
Acrididae |
Acrididae |
Legs |
12 |
0.398 |
|
46 |
Agriolimacidae |
Deroceras sp. |
Whole body
(Observed) |
2 |
0.066 |
|
47 |
Carabidae |
Bradycellus sp. |
Elytra and legs |
4 |
0.133 |
|
48 |
Carabidae |
Harpalinae |
Elytra and legs |
5 |
0.166 |
|
49 |
Carabidae |
Stenolophus sp. |
Elytra and legs |
2 |
0.066 |
|
50 |
Carabidae |
Platynus sp. |
Elytra |
5 |
0.166 |
|
51 |
Cerambycidae |
Cerambycidae |
Legs, exoskeleton,
ommatidium |
8 |
0.265 |
|
52 |
Chrysomelidae |
Altica sp. |
Elytra |
1 |
0.033 |
|
53 |
Chrysomelidae |
Chrysolina sp. |
Legs |
2 |
0.066 |
|
54 |
Dermaptera |
Dermaptera |
Exoskeleton |
1 |
0.033 |
|
55 |
Fanniidae |
Fannia sp. |
Exoskeleton |
7 |
0.232 |
|
56 |
Lucanidae |
Lucanidae |
Elytra |
2 |
0.066 |
|
57 |
Lumberculidae |
Lumbriculidae |
Whole body
(Observed) |
8 |
0.265 |
|
58 |
Ptinidae |
Stegobium paniceum |
Full body |
1 |
0.033 |
|
59 |
Invertebrates |
Invertebrates |
Elytra,
exoskeleton, legs, Mesonotum, scutellum, |
169 |
5.607 |
|
|
Freshwater
invertebrates |
|
|||
|
60 |
Aeshinidae |
Aeshnidae |
Exoskeleton |
1 |
0.033 |
|
61 |
Athericidae |
Athericidae |
Whole body
(Observed) |
2 |
0.066 |
|
62 |
Aphelocheiridae |
Aphelocheirus sp. |
Elytra |
2 |
0.066 |
|
63 |
Blepharicidae |
Blephariceridae |
Exoskeleton |
1 |
0.033 |
|
64 |
Belostomatidae |
Diplonychus sp. |
Legs and wings |
3 |
0.100 |
|
65 |
Chironomidae |
Chironomidae (red) |
Exoskeleton |
10 |
0.332 |
|
66 |
Corixidae |
Hesperocorixa interrupta |
Wavy leopard
pattern elytra |
21 |
0.697 |
|
67 |
Dytiscidae |
Rhantus sp. |
Dotted leopard
pattern elytra |
19 |
0.630 |
|
68 |
Hydropsychidae |
Hydropsychidae |
Femur |
1 |
0.033 |
|
69 |
Hydroptilidae |
Hydroptilidae |
Case with insect |
1 |
0.033 |
|
70 |
Lymnaeidae |
Orientogalba ollula |
Part of shell |
9 |
0.299 |
|
71 |
Potamidae |
Potamidae |
Legs, carapace,
exoskeleton |
16 |
0.531 |
|
72 |
Psychomyiidae |
Psychomyiidae |
Trochatin |
2 |
0.066 |
|
73 |
Scirtidae |
Scirtidae |
Exoskeleton |
1 |
0.033 |
|
74 |
Sphaeriidae |
Pisidium sp. |
Shell |
5 |
0.166 |
|
75 |
Tipulidae |
Tipulidae |
Whole body |
3 |
0.100 |
|
|
Others |
|
|||
|
76 |
|
Birds |
Feather |
2 |
0.066 |
|
77 |
|
Fish |
Scale/skin |
2 |
0.066 |
|
78 |
|
Plastics |
With different
colors: White, red, pink, yellow, green, blue |
17 |
0.564 |
|
79 |
|
Pebbles |
With color and
patterns: black stripe, white, and yellow |
13 |
0.431 |
|
|
|
|
|
3014 |
100.00 |
For
image & figures - - click here for
full PDF
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