Journal of Threatened Taxa | www.threatenedtaxa.org | 26 November 2025 | 17(11): 27889–27896

ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)

https://doi.org/10.11609/jott.9940.17.11.27889-27896

#9940 | Received 22 May 2025 | Final received 29 September 2025 | Finally accepted 25 October 2025

Avian composition and distribution in the bird sanctuary planning zone of Can Gio Mangrove Biosphere Reserve, Ho Chi Minh City, Vietnam

Huynh Duc Hieu ¹, Huynh Duc Hoan ²*, Bui Nguyen The Kiet ³, Dang Ngoc Hiep ⁴,

Nguyen Thi Phuong Linh ⁵ & Nguyen Dang Hoang Vu ⁶*

^1–5 Management Board of Protection and Special-use Forests of Ho Chi Minh City, 176 Hai Ba Trung Street, Tan Dinh Ward, Ho Chi Minh City, Vietnam.

⁶ Institute of Life Science, Vietnam Academy of Science and Technology, 9/621, Vo Nguyen Giap Street, Linh Xuan, Chi Minh City, Vietnam.

¹ huynhduchieu.7879@gmail.com, ² huynhduchoanpy@gmail.com, ³ joankietthe@gmail.com, ⁴ hqt.ngochiep93@gmail.com, ⁵ ntplinh1709@gmail.com, ⁶ nguyendanghoangvu888@gmail.com

(^2,6 *corresponding authors)

Editor: H. Byju, Coimbatore, Tamil Nadu, India. Date of publication: 26 November 2025 (online & print)

Citation: Hieu, H.D., H.D. Hoan, B.N.T. Kiet, D.N. Hiep, N.T.P. Linh & N.D.H. Vu (2025). Avian composition and distribution in the bird sanctuary planning zone of Can Gio Mangrove Biosphere Reserve, Ho Chi Minh City, Vietnam. Journal of Threatened Taxa 17(11): 27889–27896. https://doi.org/10.11609/jott.9940.17.11.27889-27896

Copyright: © Hieu 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: The project was funded by the Youth Science and Technology Incubator Program, managed by the Center for Youth Science and Technology Development - Ho Chi Minh City Youth Union and the Department of Science and Technology of Ho Chi Minh City, under contract No. 30/2024/HD-KHCNT-VU, “Composition and distribution of bird species in the Can Gio Mangrove Biosphere Reserve”.

Competing interests: The authors declare no competing interests.

Author details: Huynh Duc Hieu, specialist at the Forest Protection Management Department, Management Board of Protective and Special-use Forests of Ho Chi Minh City. He has over four years of experience in forest resource management and mangrove ecosystem conservation including monitoring forest resource dynamics, implementing biodiversity conservation programs, and supporting forest restoration and silvicultural projects. Huynh Duc Hoan, director of the Management Board of Protective and Special-use Forests of Ho Chi Minh City. With 26 years of experience, he leads the management, protection, and sustainable development of the city’s protective forests and the Can Gio Mangrove Biosphere Reserve. His expertise includes silviculture, biodiversity assessment, conservation management, ecotourism, and environmental education. Bui Nguyen The Kiet, with 18 years of experience in forest resource management and biodiversity conservation. He leads Resource Development and Cooperation at the Management Board of Protective and Special-use Forests of Ho Chi Minh City. His work focuses on strategic planning and sustainable development within mangrove ecosystems and biosphere reserves to strengthening ecosystem resilience and community engagement. Dang Ngoc Hiep, specialist in the Department of Resource Development and Cooperation. With nine years of experience, she contributes to the management and sustainable development of protective forests, including the Can Gio Mangrove Biosphere Reserve. Her interests cover silviculture, biodiversity assessment, conservation management, ecotourism, and environmental education. Nguyen Thi Phuong Linh, forestry engineer at the Department of Resource Development and Cooperation, with over three years of experience in forest resource management and mangrove conservation. She works on monitoring forest changes, supporting forest development programs, and coordinating community-based activities. She also implements environmental communication and education initiatives in conservation. Nguyen Dang Hoang Vu, researcher at the Institute of Life Science, Vietnam Academy of Science and Technology, with 13 years of experience. His work focuses on biodiversity, including integrative taxonomy, species discovery, ecology, and distribution modeling. He develops conservation strategies for threatened species, engages citizen scientists, sustainable amphibian and reptile farming.

Author contributions: Huynh Duc Hieu developed the research idea. Huynh Duc Hieu, Bui Nguyen The Kiet, Dang Ngoc Hiep and Nguyen Thi Phuong Linh collected the data. Dang Ngoc Hiep and Huynh Duc Hieu analysed the data and wrote the first draft. Huynh Duc Hoan, Huynh Duc Hieu and Nguyen Dang Hoang Vu edited the final draft. Nguyen Dang Hoang Vu submitted the manuscript to the journal.

Acknowledgements: The project was funded by the Youth Science and Technology Incubator Program, managed by the Center for Youth Science and Technology Development - Ho Chi Minh City Youth Union and the Department of Science and Technology of Ho Chi Minh City, under contract No. 30/2024/HD-KHCNT-VU, “Composition and distribution of bird species in the Can Gio Mangrove Biosphere Reserve”. We would like to thank the Management Board of Protection and Special-use Forests of Ho Chi Minh City for allowing this research, and the Department of Natural Resources Management and Development for their support during the field survey, data collection and processing. We would like to thank the anonymous reviewers and the editorial team for their useful comments to improve the article.

Abstract: Six field surveys were conducted from July 2024 to May 2025 in six sessions (three during dry and three during wet seasons) along 10 fixed transects (five in the core zone and five in the buffer zone) to assess the bird species composition and spatial distribution in the bird sanctuary planning zone of the Can Gio Mangrove Biosphere Reserve, after 47 years of restoration (1978–2025). A total of 57 bird species, representing 11 orders, 32 families, and 45 genera were recorded, including 18 waterbird species. Four species are listed as threatened and prioritized for conservation by the IUCN Red List: Porzana paykullii as Near Threatened, Vietnam Red List Book: Anhinga melanogaster and Mycteria leucocephala as Vulnerable, and Vietnamese law: Milvus migrans and Anhinga melanogaster as prioritized for conservation. The order Passeriformes was the most species-rich (21 species), while Pelecaniformes had the highest number of individual encounters (2,427). Overall, bird diversity in the area was relatively high (Shannon-Wiener index H’ = 2.60 ± 0.34), with a moderate level of dominance (Simpson D = 0.12 ± 0.06). Species abundance was uneven across seasons and transects, with higher diversity and abundance during the wet season, although the differences were not statistically significant. Only the transect L8 in the buffer zone showed statistically significant differences in diversity and abundance, representing a newly recorded breeding area dominated by waterbird species such as Nycticorax nycticorax, Egretta garzetta, Ardea intermedia, and Microcarbo niger. Compared to a 2019 study, the number of breeding species in the core zone declined to seven species with approximately 1,000 individuals, while a new breeding area in the buffer zone was identified with eight breeding species and approximately 1,500 individuals. Continuous monitoring and conservation efforts are necessary to sustain and manage avian biodiversity in this critical wetland ecosystem.

KEYWORDS: Species diversity, biological index, breeding ecology, habitat use, core and buffer zones, conservation priority species, seasonal variation, waterbirds, avifauna.

Introduction

Waterbirds are key indicators of wetland health and play critical ecological roles as predators, seed dispersers, and contributors to nutrient cycling (Byju et al. 2025a). Across Asia, particularly along coastal zones, wetlands support rich avifaunal diversity but are increasingly threatened by habitat loss, pollution, and human disturbance. Long-term monitoring in India has revealed marked declines in the abundance and breeding success of both migratory and resident waterbirds due to anthropogenic pressures (Byju et al. 2025b,c). These findings underscore the urgent need to assess and monitor waterbird communities in other Asian coastal ecosystems, where comparable data remain scarce.

Vietnam is one of the 22 countries along the East Asian-Australasian Flyway Partnership (EAAFP), which supports the diversity of migratory birds and hosts about 40% of the world’s migratory bird species (Yamaura et al. 2017). Vietnam’s avifauna is highly diverse, with over 900 species documented (Le 2020), including 53 species listed as threatened in the country (Ministry of Science and Technology 2007) and 10 endemic species (Tran 2020). However, despite Vietnam’s strategic importance along the flyway, comprehensive site-based assessments of waterbird communities remain limited.

The Can Gio Mangrove Biosphere Reserve (CGMBR) in southern Vietnam represents the largest rehabilitated mangrove forest in southeastern Asia and serves as a critical breeding and stopover site for numerous waterbird species. Previous surveys documented 164 bird species across 51 families and 15 orders (Le 2021), including five nationally protected and 16 globally threatened species (IUCN 2025). Yet, these studies were spatially and temporally restricted, focusing mainly on the core zone (Huynh et al. 2019). Consequently, current knowledge about the distribution and composition of waterbirds across the broader bird sanctuary planning zone—including both core and buffer zones—remains incomplete.

Given the ongoing coastal development and mounting anthropogenic pressures on mangrove ecosystems, updated information is urgently needed to evaluate the outcomes of nearly five decades of forest restoration and to guide effective conservation management. This study aims to (1) document the current species composition and distribution of waterbirds in the bird sanctuary planning zone of CGMBR, and (2) provide baseline data for long-term monitoring and habitat management.

Materials and methods

Can Gio Mangrove Biosphere Reserve (CGMBR) is Vietnam’s first UNESCO Biosphere Reserve, recognized on 21 January 2000 and is part of the “discontinuous biodiversity corridor” planning initiative for the 2020–2030 period under decision no. 1250/QD-TTg of the Vietnam Prime Minister on 31 July 2013 (Can Gio District Forest Protection Management Board 2025). As part of CGMBR, the bird sanctuary planning zone, located at Vam Sat in subzone 15a, encompasses 602.5 ha buffer zone and 126.2 ha in the core zone. The entire bird sanctuary planning zone was designated for protection by Decision No. 27/QD-UB on 06 January 2004 (Chairman of Ho Chi Minh City People’s Committee 2004).

Ten fixed transects were established across the bird sanctuary planning zone, covering different habitat types: natural forest (4 transects), plantation forest (3 transects), and other land types, including pond banks, and salt fields adjacent to forested areas (3 transects) (Figure 1). Five transects were in the core zone in the same area as Huynh et al. (2019) (L1–5), and five in the buffer zone (L6–10). Each transect was 500 m in length with a 20 m observation radius.

Field surveys were conducted in six sessions: three in the dry season (November 2024–April 2025) and three in the wet season (May–October 2025), with monthly intervals. Observations were carried out from 0700 h to 1130 h. Birds were identified based on morphology, size, plumage, and vocalizations. Unidentified species were documented with photographs and sound recordings for later verification using field guides (Vo 1981; King et al. 1997; Nguyen et al. 2000; Koshiyama & Asano 2019) and the Birds of South East Asia website (Vietnam Wildlife Photography Club 2025). Taxonomy followed the Avibase.

Collected data were analysed using BioDiversity Professional 2.0 (McAleece et al. 1997) and Statgraphics XIX (Nguyen 2009). Three biodiversity indices were used to assess community structure, including Shannon-Wiener index (H’, to evaluate species diversity) (Shannon & Wiener 1963), Simpson’s dominance index (D, to measure species dominance) (Simpson 1949), and Sorensen similarity index (SI, to compare species similarity among transects) (Shannon & Wiener 1963). Diversity categories followed standard classifications: H’ < 0.6 = low diversity; 0.6 ≤ H’ ≤ 1.5 = moderate; 1.5 < H’ ≤ 2.5 = high; 2.5 < H’ ≤ 3.5 = very high; H’ > 3.5 = extremely high diversity. The lower the Simpson’s D, the higher the diversity. Sorensen Index was used to classify pairwise similarity from very low (<20%) to very high (≥80%).

In addition, biodiversity indices were compared between the wet and dry seasons to examine temporal variation in bird communities. Differences among habitat types (core zone vs. buffer zone; mixed vegetation, waterbody, and edge habitats) were also analysed to evaluate spatial patterns in avian diversity and composition. This allowed us to assess not only overall community structure but also seasonal and habitat-specific differences that may influence waterbird assemblages. Breeding bird populations were assessed by comparing current observations with data from a 2019 study.

Results and discussion

Avian composition

A total of 57 bird species belonging to 45 genera, 32 families, and 11 orders were recorded across the bird sanctuary planning zone in the Can Gio Mangrove Biosphere Reserve (CGMBR) during six surveys from July 2024 to May 2025 (July, September 2024 and May 2025 represent wet season and November 2024 and January, March 2025 represent dry season) (Table 1). The wet season (July, September 2024, and May 2025) had more species and showed higher individual encounters than the dry season (November 2024, January and March 2025), with 54 vs. 42, and 2.779 vs. 1.899, respectively (Appendix 1). Among all recorded species, 18 species were waterbirds, including four of conservation concern-—Anhinga melanogaster, Milvus migrans, Mycteria leucocephala, and Porzana paykullii—listed as Near Threatened or Vulnerable by the IUCN Red List, the Vietnam Red Data Book, and Vietnamese law (Prime Minister of Vietnam 2019, 2021). Their presence underscores the ecological and conservation importance of this wetland.

Species richness and diversity indices varied significantly across transects and between seasons (Table 2; Figures 2–3). Shannon–Wiener diversity index (H′) ranged from 1.77–2.93, indicating moderate to high diversity. The highest diversity occurred in the core zone (L10, H′ = 2.93), while the lowest was in buffer zone (L8, H′ = 1.77). In contrast, Simpson’s dominance index (D) ranged 0.06–0.16, with highest dominance also observed at L8, where bird communities were strongly dominated by Nycticorax nycticorax (827 individuals), Egretta garzetta (664), Ardea intermedia (283), and Microcarbo niger (143). This indicates that while the buffer zone (L8) had fewer species, it supported larger populations of a few dominant waterbird species.

Breeding data further support this pattern. The transect L8 recorded eight breeding bird species with approximately 1,500 individuals, while the core zone supported only seven breeding species with around 1,000 individuals–a decline from 2,000 breeding individuals recorded in 2019 (Huynh Duc Hoan et al. 2019). The Sorensen similarity index also indicated the lowest overlap between transect L8 with others sites (Figure 4), suggesting that L8 represents a distinct habitat type now more suitable for breeding. The shift in breeding activity from the core to the buffer zone may reflect localized habitat changes, possibly linked vegetation structure, prey availability, or anthropogenic disturbance.

Similar spatial and seasonal shifts in waterbird assemblages have been reported in other Asian wetlands, where breeding colonies relocate or decline under human pressure (Byju et al. 2025a,c). For instance, studies from India have shown that lagoon and estuarine with high bird abundance are often sensitive to disturbance, resulting in temporal declines in breeding success (Byju et al. 2024, 2025a,b). In CGMBR, the emergence of transect L8 as a new breeding hotspot reflects the dynamic adaptation of waterbird populations to changing habitat conditions within restored mangrove systems.

Overall, our findings highlight both the resilience and vulnerability of avian communities in the bird sanctuary planning zone. The persistence of threatened species and the establishment of new breeding colonies emphasize the conservation value and ecological recovery potential of restored mangroves. However, the decline of core zone breeders indicates emerging habitats stress. Continuous, long-term monitoring, similar to those conducted in other Asian wetlands (Byju et al. 2025b), is therefore essential to evaluate restoration outcomes, detect ecological shifts, and guide adaptive conservation management in this UNESCO-designated biosphere reserve.

Conclusion

The bird sanctuary planning zone within the Can Gio Mangrove Biosphere Reserve supports a relatively high diversity of bird species including four globally and nationally threatened taxa. The discovery of a new breeding area in the buffer zone (transect L8) and the decline in species abundance in the core zone emphasize the need for adaptive management and continuous monitoring.

Preserving the ecological integrity of this wetland is vital for sustaining its role as a key habitat for waterbirds, especially during the breeding season. Future conservation efforts should prioritize habitat protection, environmental education, and the mitigation of anthropogenic pressures to maintain avian biodiversity in this region.

Table 1. Bird species composition in the bird sanctuary planning area.

	Scientific name	Dry season	Rainy season	Conservation status
				1	2	3
	I. ACCIPITRIFORMES
	1. Accipitridae
1	Milvus migrans (Boddaert, 1783)	-	1	-	LC	IIB
	II. ANSERIFORMES
	2. Anatidae
2	Anas platyrhynchos Linnaeus, 1758*	-	2	-	LC	-
	III. APODIFORMES
	3. Apodidae
3	Aerodramus germani Oustalet, 1876	278	232	-	-	-
	IV. CHARADRIIFORMES
	4. Laridae
4	Chlidonias hybrida (Pallas, 1811)*	-	2	-	LC	-
5	Chroicocephalus ridibundus (Linnaeus, 1766)*	1	-	-	LC	-
	5. Recurvirostridae
6	Himantopus himantopus (Linnaeus, 1758)*	43	16	-	LC	-
	6. Scolopacidae
7	Tringa glareola Linnaeus, 1758*	16	2	-	LC	-
8	Tringa nebularia (Gunnerus, 1767)*	-	2	-	LC	-
	V. COLUMBIFORMES
	7. Columbidae
9	Streptopelia chinensis (Scopoli, 1786)	33	41	-	-	-
10	Streptopelia tranquebarica (Hermann, 1804)	2	4	-	LC	-
11	Treron bicinctus (Jerdon, 1840)	2	1	-	LC	-
12	Treron vernans (Linnaeus, 1771)	2	11	-	-	-
	VI. CORACIIFORMES
	8. Alcedinidae
13	Alcedo atthis (Linnaeus, 1758)	9	13	-	LC	-
14	Halcyon smyrnensis (Linnaeus, 1758)	-	3	-	LC	-
15	Todiramphus chloris (Boddaert, 1783)	61	98	-	LC	-
	9. Meropidae
16	Merops superciliosus Linnaeus, 1766		4	-	LC	-
	VII. CUCULIFORMES
	10. Cuculidae
17	Centropus sinensis (Stephens, 1815)	9	30	-	LC	-
18	Cuculus micropterus Gould, 1837	1	-	-	LC	-
	VIII. GRUIFORMES
	11. Rallidae
19	Amaurornis phoenicurus Pennant, 1769	3	3	-	LC	-
20	Porzana fusca Linnaeus, 1766	2	1	-	LC	-
21	Porzana paykullii (Ljungh, 1813)	2	-	-	NT	-
22	Rallus striatus (Linnaeus, 1766)	4	5	-	-	-
	IX. PASSERIFORMES
	12. Acanthizidae
23	Gerygone sulphurea Wallace, 1864	78	121	-	LC	-
	13. Cisticolidae
24	Orthotomus ruficeps (Lesson, 1830)	-	2	-	LC	-
25	Orthotomus sepium Horsfield, 1821	73	97	-	LC	-
26	Prinia inornata Sykes, 1832	-	2	-	LC	-
	14. Corvidae
27	Crypsirina temia (Daudin, 1800)	13	36	-	LC	-
	15. Dicaeidae
28	Dicaeum cruentatum (Linnaeus, 1758)	-	16	-	LC	-
29	Dicaeum ignipectus (Blyth, 1843)	-	3	-	LC	-
	16. Estrildidae
30	Lonchura punctulata (Linnaeus, 1758)	13	32	-	LC	-
	17. Motacillidae
31	Motacilla alba Linnaeus, 1758	34	30	-	LC	-
	18. Muscicapidae
32	Copsychus malabaricus (Scopoli, 1786)	-	1	-	LC	-
33	Copsychus saularis (Linnaeus, 1758)	50	65	-	LC	-
	19. Paridae
34	Parus minor Temminck & Schlegel, 1848	7	5	-	-	-
	20. Passeridae
35	Passer flaveolus Blyth, 1845	13	15	-	LC	-
36	Passer montanus (Linnaeus, 1758)	5	4	-	LC	-
	21. Pellorneidae
37	Graminicola bengalensis Jerdon, 1863	-	5	-	LC	-
	22. Phylloscopidae
38	Phylloscopus fuscatus (Blyth, 1842)	-	6	-	LC	-
	23. Ploceidae
39	Ploceus philippinus (Linnaeus, 1766)	3	2	-	LC	-
	24. Pycnonotidae
40	Pycnonotus goiavier (Scopoli, 1786)	62	80	-	LC	-
	25. Rhipiduridae
41	Rhipidura javanica (Sparrman, 1788)	66	49	-	LC	-
	26. Sturnidae
42	Acridotheres grandis Moore, 1858	-	17	-	LC	-
	27. Zosteropidae
43	Zosterops palpebrosus (Temminck, 1824)	30	27	-	LC	-
	X. PELECANIFORMES
	28. Anhingidae
44	Anhinga melanogaster Pennant, 1769*	4	3	-	NT	IB
	29. Ardeidae
45	Ardea alba Linnaeus, 1758*	105	12	-	LC	-
46	Ardea cinerea Linnaeus, 1758*	1	10	-	LC	-
47	Ardea intermedia Wagler, 1829*	180	194	-	LC	-
48	Ardea purpurea Linnaeus, 1766*	1	6	-	LC	-
49	Ardeola bacchus (Bonaparte, 1855)*	-	5	-	LC	-
50	Ardeola speciosa (Horsfield, 1821)*	1	9	-	LC	-
51	Butorides striata (Linnaeus, 1758)*	3	14	-	LC	-
52	Egretta garzetta (Linnaeus, 1766)*	370	585	-	LC	-
53	Nycticorax nycticorax (Linnaeus, 1758)*	247	645	-	LC	-
	30. Ciconiidae
54	Mycteria leucocephala (Pennant, 1769)*	-	39	VU	LC	-
	31. Phalacrocoracidae
55	Microcarbo niger (Vieillot, 1817)*	60	142	-	LC	-
	XI. PICIFORMES
	32. Picidae
56	Chrysocolaptes lucidus (Scopoli, 1786)	1	11	-	LC	-
57	Picus vittatus Vieillot, 1818	11	18	-	LC	-

Note: -—unrecorded/not listed in IUCN or Vietnamese law | Conservation status: 1—in Vietnam Red List Book (2007) | 2—in IUCN Red List (2025): VU—Vulnerable | NT—Near Threatened | LC—Least Concern | 3—according to Decree 06/2019/ND-CP dated 22 January 2019 and updated by Decree 84/2021/ND-CP dated 22 September 2021 of the Government | *—waterbird.

For figures & image - - click here for full PDF

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Appendix 1. Species counts (SC) and individual encounters (IE) in survey transects.

Transect		L1	L2	L3	L4	L5	L6	L7	L8	L9	L10	Total
All transects	IE	204	256	387	219	242	188	327	2,197	515	143	4,678
	(%)	4.4	5.5	8.3	4.7	5.2	4.0	7.0	47.0	11.0	3.1	100.0
	SC	21	28	32	29	25	24	35	33	36	25	57
	(%)	36.8	49.1	56.1	50.9	43.9	42.1	61.4	57.9	63.2	43.9	100.0
Dry season	IE	91	135	162	70	83	81	122	726	383	46	1,899
	(%)	4.8	7.1	8.5	3.7	4.4	4.3	6.4	38.2	20.2	2.4	100.0
	SC	17	20	22	19	16	14	24	22	23	15	42
	(%)	41.5	48.8	53.7	46.3	39.0	34.1	58.5	53.7	56.1	36.6	100.0
Rainy season	IE	113	121	225	149	159	107	205	1,471	132	97	2,779
	(%)	4.1	4.4	8.1	5.4	5.7	3.9	7.4	52.9	4.7	3.5	100.0
	SC	20	23	28	23	22	21	27	29	32	23	54
	(%)	37.7	43.4	52.8	43.4	41.5	39.6	50.9	54.7	60.4	43.4	100.0