Journal of Threatened Taxa |
www.threatenedtaxa.org | 26 April 2021 | 13(5): 18110–18121
ISSN 0974-7907 (Online) | ISSN 0974-7893
(Print)
https://doi.org/10.11609/jott.6760.13.5.18110-18121
#6760 | Received 02 October 2020 | Final
received 01 November 2020 | Finally accepted 15 April 2021
Conservation ecology of birds in Mt. Hilong-hilong,
a Key Biodiversity Area on Mindanao Island, the Philippines
Arturo G. Gracia Jr.1*, Alma B. Mohagan2, Janezel C. Burlat3, Welfredo
L. Yu Jr.4, Janine Mondalo5, Florfe
M. Acma6, Hannah P. Lumista7, Riah
Calising8 & Krizler Cejuela Tanalgo9*
1Department of Natural
Sciences and Mathematics, College of Arts and Sciences, Surigao
del Sur State University (Main Campus), Rosario, Tandag
City 8300, Surigao del Sur, the Republic of the
Philippines.
1,3,4,5,8Department of
Secondary Education, College of Teacher Education, Surigao
del Sur State University (Main Campus), Rosario, Tandag
City 8300, Surigao del Sur, the Republic of the
Philippines.
1,2,6,7The Graduate School,
Central Mindanao University, Musuan, Maramag, Bukidnon 8714, Philippines.
2,6,7Department of
Biology, College of Arts and Sciences, Central Mindanao University, Musuan, Maramag, Bukidnon 8714,
the Republic of the
Philippines.
9Landscape Ecology
Group, Center for Integrative Conservation, Xishuangbanna Tropical Botanical Garden, Menglun, Mengla 6663030, Yunnan
Province, P.R. China.
9Center of
Conservation Biology, Core Botanic Gardens, Chinese Academy of Sciences, Menglun, Mengla 6663030,
Yunnan Province, P.R.
China.
9International
College, University of the Chinese Academy of Sciences, Beijing 100049, P.R.
China.
9Department of
Biological Sciences, College of Science and Mathematics, University of Southern
Mindanao, Kabacan 9407,
North Cotabato, the Republic of the Philippines.
1 artzgracia@gmail.com
(corresponding author), 2 almamohagan@gmail.com, 3 janezel027@gmail.com,
4 welfredoyu@gmail.com,
5 janinemondalo96@gmail.com,
6 flmacma@gmail.com, 7 hlumista@yahoo.com, 8 riahcalising24@gmail.com,
9 tkrizler@gmail.com (corresponding
author). *These authors contributed equally to the manuscript
and share senior authorship
Editor: Namaal De Silva, The George Washington
University, Washington, USA. Date
of publication: 26 April 2021 (online & print)
Citation: Gracia
Jr. A.G., A.B. Mohagan, J.C. Burlat,
W.L. Yu Jr, J. Mondalo, F.M. Acma,
H.P. Lumista, R. Calising
& K.C. Tanalgo (2021). Conservation ecology
of birds in Mt. Hilong-hilong, a Key Biodiversity
Area on Mindanao Island, the Philippines. Journal of Threatened
Taxa 13(5): 18110–18121. https://doi.org/10.11609/jott.6760.13.5.18110-18121
Copyright: © Gracia Jr. et al. 2021. 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: None.
Competing interests: The authors
declare no competing interests.
Author details: AGG is a field
biologist working on terrestrial vertebrates including birds. He is a university instructor. ABM is a
Professor and head of CMU museum. Her research interests are focused on
monitoring terrestrial fauna in different forest ecosystems of the Philippines.
FMA is a Professor. She is currently the director of the Center
for Biodiversity Research and Extension in Mindanao (CEBREM). Her research
focuses on the conservation of wildlife flora and fauna in the
Philippines. HPL is a Professor and the
curator of the Botany section of CMU museum. Her research interest deals on
taxonomy and ecology of flora and fauna.
JM is a STEM Teacher at the Purisima Diocesan School Inc. Her research interest is about the
integration of education towards conservation.
JB is a biological science educator practitioner. Her research interest is on the taxonomy of
birds. WY is a biological science
educator practitioner. His research
interest is about the taxonomy of birds.
RC is a biological science educator practitioner. Her research interest is on the taxonomy of
birds. KCT is an early-career
conservation biologist working on developing tools for conservation prioritisation
and a doctoral candidate at the Center for
Integrative Conservation of Chinese Academy of Science’s Xishuangbanna
Tropical Botanical Garden in Yunnan, China.
Author contribution: AGG, ABM, FMA, and
HPL conceptualised the project. AGG, JM, JB, WYJ, and RC carried out the
fieldwork. AGG and KCT performed data
curation and analyses. KCT performed the
visualisation. KCT led the manuscript
writing. All authors reviewed, edited,
and approved the submission of the final version of the manuscript.
Acknowledgements: This manuscript was
crafted amidst the global COVID-19 pandemic, in which writing, and reviewing
were challenging for both the authors and the editorial process. We would like to thank the three anonymous
reviewers and the editors of JoTT for their
constructive comments that benefited the improvement of the manuscript. We would like to acknowledge also the
Department of Environment and Natural Resources (DENR) for the issuance of GP,
the Local Government Unit of Awasian and Tandag Water District for the logistical support, and to
all the people who contributed to the success of this endeavour.
Abstract: The identification of
key areas for conservation and protection according to science-based evidence
is an important component to circumvent the negative impacts of environmental
changes within geopolitical territories and across the globe. Priority areas for biodiversity played an
important role to ensure the protection of many species particularly those that
are unique and threatened. There are
more than 200 Key Biodiversity Areas (KBAs) in the Philippines, yet many
important research and biodiversity data are either unpublished or
unconsolidated. Birds are commonly
studied indicators for KBA identification due to their high species richness,
diversity, and sensitivity to forest ecosystems. By combining data from past and present
surveys, we accounted for a total of 148 bird species of 51 families, with 20
new records from recent field surveys.
Our analysis showed a high level of endemism within Mt. Hilong-hilong with 36% Philippine endemic, 14% restricted
to Mindanao faunal region and 11% migrant. In terms of conservation, 8% of the
species were considered in threatened categories. The species richness and endemism were higher
in lowland to mid-elevation areas compared to higher elevation areas of the
KBA. Endemism (i.e., Mindanao endemic)
and increasing body mass were important determinants of binary extinction risk
for bird species in Mt. Hilong-hilong. The high biodiversity in Mt. Hilong-hilong indicates an example of the vital role of
KBAs in preserving nationally and globally important bird species. Lastly, we emphasise the importance of
collaboration and integrating past and present information to synthesise
relevant information to complement ongoing conservation efforts in Mt. Hilong-hilong and other key habitats in the Philippines.
Keywords: Anthropocene,
collaboration, deforestation, ecological indicators, endemism.
Introduction
The Philippines is
the world’s second-largest archipelago and its unique biogeographical features
with more than 7,000 islands allowed the diversification of taxa, making it one
of the megadiverse tropical country (Heaney & Regalado 1998). Birds are amongst the most diverse group in
the Philippines, constituting more than 50% of the country’s land vertebrates,
and large proportions are considered distinct and globally threatened (Peterson
et al. 2000), with 724 described species and at least 200 country endemics
(Clements et al. 2019). These numbers
will probably increase with proper taxonomic studies when integrative taxonomy
approach is made (Sánchez-González & Moyle 2011; Gonzalez et al. 2013).
The diversity of
birds in the Philippine contributes to the ecological balance and integrity of
remnant native vegetation (Peterson et al. 2000). Birds have large range distribution, high
mobility, and diverse traits that are sensitive to ecological changes
(O’Connell et al. 2000; Trindade-Filho et al. 2012). Therefore high avian species richness can
serve as an important ecological indicator in terrestrial ecosystems
(Canterbury et al. 2000). The functional
trait diversity across birds provides various key ecosystem services in
different systems, from intact forests to more disturbed urbanised areas (Sekercioglu et al. 2016).
Frugivorous and nectarivorous birds are vital
for seed dispersal and pollination, respectively, therefore maintain gene flow
and persistence of the population of many important tropical plant species
(Ingle 2003; García & Martínez 2012).
This group also serves as natural foresters in degraded areas through
seed rain and dispersal (Gonzales et al. 2009; Mueller et al. 2014). Insectivorous birds can suppress insect pests
and can reduce the use of environmentally harmful pesticides in agricultural
landscapes (Koh 2008; Sekercioglu 2012). Carnivores are vital in the check and balance
of prey populations, for example, rodent populations in urban or agricultural
landscapes with high reproductive potential (Donázar
et al. 2016).
The Philippine
biodiversity, however, is threatened by various environmental and human
pressures (Brooks et al. 1999) that may disrupt species diversity, their
ecological function and services. Given
the growing population in the Philippines, a large proportion of species and
habitats are threatened by land-use changes to accommodate human needs (Brooks
et al. 2002; Posa & Sodhi
2006; Posa et al. 2008). In the Philippines, over 67% of bird species
are dependent on intact pristine forests ( Dutson et
al. 1993; Brooks et al. 1999; Gonzales et al. 2009). Deforestation poses a key threat to
biodiversity loss in the country, driven by logging and shifting
agriculture. For example, at least 74%
of tree cover loss in 2001–2018 was caused by deforestation alone (Global
Forest Watch 2020). In 2002–2019, an
estimated 3.1% or 145,000ha of humid forest was lost in the Philippines,
equivalent to a 12% tree cover loss (Global Forest Watch 2020).
The quality of the
environment plays an important role in shaping the structure and function of
biodiversity (Fried et al. 2019; Lelli et al. 2019),
generally described using population density, species abundance, trait
diversity, and distribution across different habitats (Davidar
et al. 2005). To prevent eventual
decline and species extinction, important areas for conservation such as Key
Biodiversity Areas (KBAs) are identified by conservation biologists and
respective governmental policymakers based on high biodiversity potential. KBA identification is not solely dependent on
the species richness but in accordance to the presence of population or species
that are (1) threatened globally, (2) distributed in a small restricted range
(e.g., endemism), (3) restricted use during some stage of their life cycle, and
lastly (4) restricted to a specific biome (Eken et
al. 2004; Ambal et al. 2012). Birds are included as indicator groups for
terrestrial KBAs identification due to their wide-breadth of diversity and
sensitivity to ecosystem conditions (Canterbury et al. 2000; O’Connell et al.
2000; Eken et al. 2004). Currently, there are 228 KBAs in the
Philippines, of which 101 are terrestrial (51,249 km2) and 27 are
fully protected, 25 partially protected, and 49 unprotected (Ambal et al. 2012).
Although KBAs holds high biodiversity, not all are protected, and thus
often challenged by several factors, particularly anthropogenic activities due
to lack of well-defined statuary protection policy prohibiting encroachments
and the persistence of threats (Butchart et al. 2015; Cai 2013; Knight et al.
2007). The effectiveness of conservation
policies and initiatives often requires extensive and wide information on
biodiversity, yet knowledge gaps continue to be a challenge, limiting effective
and efficient decision making (Butchart et al. 2015; Nori et al. 2020).
The Island of
Mindanao in the southern part of the Philippines holds many biodiversity-rich
ecosystems with a high concentration of endemic species (Paz et al. 2013; Sanguila et al. 2016; Amoroso et al. 2019). The majority of the endemic and threatened
species are concentrated in intact forests identified or protected by the
government to conserve the species from total extinction (Sanguila
et al. 2016; Amoroso et al. 2019).
Mt. Hilong-hilong (Fig. 1) is a KBA in Mindanao that lies on
the boundaries of Agusan del Sur, Agusan del Norte, and Surigao del
Sur Provinces in the northern portion of the Diwata
Range of northeastern Mindanao or Caraga
region. The whole KBA has an area of
2,432km2 with the highest elevation at 2,012 metres above sea level
(The Haribon Foundation 2018). Several taxonomic and biodiversity studies
have been conducted in Mt. Hilong-hilong, focusing
particularly on birds. Albeit
information remains scattered or inaccessible.
A major knowledge gap concerning Philippine birds in KBAs is the lack of
clear understanding of the relationship of species diversity, the extent of the
threatening process, and extinction risks.
Understanding biotic potential and vulnerability are essential to
developing effective conservation prioritisation in a certain habitat or
ecosystems (Segan et al. 2016; Tanalgo & Hughes 2019). Here, we integrate field data collected in
2017 and the past survey to assess and analyse the overall biotic potential and
diversity patterns for birds in Mt. Hilong-hilong in
Mindanao Island, Philippines. Our study
further aims to understand the conservation priorities of birds in this KBA
based on their ecological status and potential threats. Our synthesis will serve as complementary
science-based evidence to support ongoing conservation efforts in Mt. Hilong-hilong.
Materials and methods
Entry protocol and
acquisition of permit
Prior to the field
surveys, as a courtesy, we visited the major stakeholders from the local
government and the local people in the area.
This was followed by obtaining of the Wildlife Gratuitous Permit (GP #
R13-2017-0036) following the procedure of the Department of Environment and
Natural Resources (DENR) of the Republic of the Philippines.
Field survey
We conducted field
surveys in Tandag Watershed in Mt. Hilong-hilong, Barangay Awasian, Tandag City, Surigao del Sur,
situated between 9.075o N and 126.154o E. We primarily recorded birds using transects
and point counts. We utilised
established trails to establish 2-km transects in each elevation range. Birds were observed during peak activity,
from 05.00h to 10.00h and from 14.00h to 18.00h, for four consecutive days per
transect with five field researchers as observers. The samplings were performed in the first
four days for transect 1 and the next four days for transect 2. The overall sampling effort was 180
observer-hours per transect. Point
counts were carried out at every 250m of the transect
making a 9-point station on a 2-km transect line. We conducted surveys for 20 minutes at every
point. All bird species observed and vocalisations
during the transect walk and in the point-stations were counted.
We also performed
mist-netting to supplement the sampling.
We set 22 standard-sized mist nets in every site at the heights: ground
nets (0–5 m above the ground; N= 8), sub-canopy nets (at 5–10 m; N= 7), and
canopy nets (10m above ground; N= 7), to capture ground-dwelling, sub-canopy, and
canopy-dwelling species, respectively. A
total of 168 net-days was carried out.
We checked nets as regularly as possible to ensure no individuals are
tangled for a long period. Captured
individuals were placed in a cloth bag to avoid further stress, and were then
identified using field guides by (Kennedy et al. 2000). All captured individuals were released in the
same area where they are captured.
Synthesis of
secondary data and analyses
We performed a simple
meta-analysis to evaluate the diversity patterns of birds in Mt. Hilong-hilong by combining present survey data and
previously published accounts. We only
included those studies that contain a complete dataset that includes elevation
of records, species name, conservation status, endemism, and feeding
guilds. We curated and updated the
species names and their species-specific information using the data from the
International Union for the Conservation of Nature Red List (IUCN 2020). We exclude in the final analysis those
species with dubious identification and ecological status. The elevation of species where the species
was recorded was binned in intervals (e.g., 0–100, 101–500, 500–1,000,
1,000–2,000 m) as representative of lower to higher elevation gradients. We determined species feeding guilds based on
published literature (e.g., Kennedy et al. 2000; Mohagan
et al. 2015; Tanalgo et al. 2015, 2019) and grouped
species into frugivores (feeding on fruits), nectarivores (feeding on nectars
and floral parts), granivores (feeding on seeds),
insectivores (feeding on insects and small arthropods), carnivores (feeding on
large invertebrates and vertebrates), and omnivores (feeding on both plant and
animal resources).
We performed all
statistical tests and data visualisations using the open-source software Jamovi 1.2.6 (The Jamovi Project
2020). We omitted
abundance-based data (e.g., species counts) to standardise the quantification
and comparison. Species richness was
based on absolute species count per elevation gradient interval. We compared richness and proportion of
ecological status, e.g., conservation status, population trends, endemism, and
feeding guilds across elevational gradient using descriptive statistics and
Chi-square test of independence (χ2). We performed simple generalised linear
modelling (GLMs) using the gamlj module in Jamovi (v 1.2.6) (Gallucci 2019) to predict the binary
extinction risk (global) of species recorded in Mt. Hilong-hilong,
with adult body mass (kg), endemism, and feeding group as explanatory
variables. We choose the best model
based on the model with the lowest Akaike information criterion (AIC) values.
We categorised and
quantified key threatening process for each species as direct human-use,
land-use driven, and natural threats using the species threat index following Tanalgo & Hughes (2019) based on the IUCN Red List
assessment (IUCN 2020) as rudimentary analysis to determine species risk from
potential threats. We classified direct
threats like those that potentially impact species biology and population
immediately (e.g., hunting and harvesting), land-use driven are threats that
affect species habitats (e.g., deforestation and agricultural conversion), and
natural threats are threats that include the climate and geological driven
threats (e.g., storm or extreme heat).
We compared the number and means of key threatening process across
endemism and conservation status using the non-parametric Kruskal-Wallis test.
Result
Bird records from the
recent field survey
A total of 82 bird
species with 20 new species records from 14 orders, 40 families, and 66 genera
were documented in the present field survey in Mt. Hilong-hilong (Supplementary Data 1 https://doi.org/10.6084/m9.figshare.13168916.v1). The number of species in the recent survey
was lower compared to the 120 reported by the Philippine Eagle Foundation
(2007) from the four other sites of Mt Hilong-hilong
located at Adlay, Sipang-pang,
Pinasandi, and RTR. White-Collared Kingfisher Todiramphus
chloris, Tricoloured Munia Lonchura
malacca, and Yellow-vented
Bulbul Pycnonotus goiavier were the most
observed species in all stations, particularly in the less forested areas, such
as grassland and cultivated-areas.
Forest-dwelling species Mindanao Hornbill Penelopides
affinis, White-eared
Brown-dove Phapitreron leucotis, and Yellow-breasted
Fruit-dove Ramphiculus occipitalis were
only observed in the dense dipterocarp forests of the KBA. In the present survey, eight per cent (N= 7
spp.) of the species were categorised as threatened. Whereas there were 52% (N= 43 spp.) endemic
species constituted by 35 (43%) species endemic in the Philippine, and eight
(10%) are endemic to Mindanao Island.
Synthesis of bird
diversity patterns in Mt. Hilong-hilong
We synthesised
present and previous studies to estimate bird species biodiversity in Mt. Hilong-hilong. We tallied a total of 148 bird species
belonging to 51 families (Supplementary Data 1 https://doi.org/10.6084/m9.figshare.13168916.v1). This number approximately represent 20% of
the 724 Philippine bird species. The
families Columbidae (N= 13 spp., 9%), Muscicapidae (N= 10 spp., 7%), Cuculidae
(N= 9 spp., 6%), Nectaridae (N= 9 spp., 6%), and Dicaeidae (N= 8 spp., 5%) were the most represented
families. Within feeding guilds, half of
the overall species were insectivorous (N= 75 spp., 51%) followed by
frugivorous (N= 28 spp., 19%), and carnivorous (N= 18 spp., 12%) (Table
1). Overall, without considering the
elevational gradient distribution, we found significant relationships between
species feeding guild and endemism (χ2= 21.7, df=
10, P= 0.016), and across conservation status (χ2= 50.9, df= 20, P< 0.001).
Thirty-six per cent
(N= 53 spp., 36%) of the species were country endemic, 20 species (14%)
restricted to Mindanao faunal region, and 16 (11%) species were migratory
(Table 1). Large proportion of species
(N= 135 spp., 91%) were considered in non-threatened category (Least Concern
and Near Threatened), eight per cent (N= 12 spp., 8%) were threatened
(Vulnerable and Endangered), and one per cent data deficient species. Although the majority of the species were
non-threatened there was a significant number of endemic species within this
category (χ2= 57.9, df= 8, P<0.001)
with 30% (N= 40 spp.) endemic in the Philippines and 10% (N= 14)
endemic in Mindanao Islands. There were
fewer number of threatened species but there was a significantly higher
percentage of species in declining population trends (N= 78 spp., 53%) versus
with stable (N= 59 spp., 40%) and increasing population trends (N= 5, 3%) (χ2=
40.70, df= 12, P< 0.001). Moreover, the 66% (N= 48 spp.) of all endemic
have significantly decreasing population trends compared to only 44% (N= 32
spp.) of the non-endemic species (χ2= 29.00, df=
6, P< 0.001) (Table 1). Furthermore, using a simple logistic
regression model, we demonstrated that adult body mass and endemism were
significant determinants of binary extinction risk of birds in Mt. Hilong-hilong. Our
best model (AIC= 136.133) indicated that larger species (β= 0.590, SE= 0.168,
P< 0.001) and those Mindanao (β= 3.227, SE= 0.864, P< 0.001)
and Philippine endemic (β= 2.557, SE= 0.802, P< 0.001) in contrast to
non-endemic species were more likely at higher risk (Fig. 2; Supplementary Data
2 https://doi.org/10.6084/m9.figshare.13169396.v1).
We found more species
in the lower elevational gradient interval (N= 115 spp., 78%) albeit presence
of particular families did not significantly differ across elevation gradient
(χ2= 110, df= 150, P<
0.994). Within the KBA, higher endemism
proportion were recorded in the lower (49%) and mid-elevation (61%) (χ2=
9.16, df= 9, P< 0.423) (Fig. 3), but
only differed significantly within conservation status (χ2= 21.60, df= 12, P< 0.04) (Fig. 3). We found no significant relationship amongst
elevational gradient and feeding guild (χ2= 9.92, df= 18, P< 0.934) (Fig. 3).
Potential threats
Fundamental to
developing effective conservation agenda is to identify potential threatening
processes and their extent. We utilized
the IUCN Red List data for each species recorded in Mt. Hilong-hilong
as a rudimentary basis for determining the extent of potential threats faced by
species; IUCN categories are globally standardised to provide a useful
framework for our analysis. Overall,
endemic and threatened species face a higher proportion of threats (Fig.
4A). Direct human use and land-use
driven threats, such as land conversions are the key potential threat for the
majority of the species (Fig. 4).
Threatening processes significantly differed across conservation status
and endemism. Overall threats
(Kruskal-Wallis test: χ2= 52.50, df=
4, P< 0.001; Land-use drive threats, χ2= 111.29, df= 4, P< 0.001; Natural threats, χ2=
27.81, df= 4, P= <0.001)
significantly differed across conservation status except for direct human
threats (Kruskal-Wallis test: χ2= 6.62, df=
4, P= 0.157) (Fig. 4B,C). When
conservation categories were compared, threatened species have higher mean
threats (mean= 3.85 ± 0.99) compared to non-threatened species (mean= 1.165 ±
1.47) (Fig. 4A).
There was a
significant difference in the number of species threatened by different threats
categories within endemism categories (Fig. 4B,C). There were 48% and 47% of threatened by
land-use driven threats in Mindanao and Philippine endemic species,
respectively (Kruskal-Wallis test: χ2= 18.02, df=
2, P< 0.001), while 84% of non-endemic species were threatened by
direct-human threats (e.g., hunting) (Kruskal-Wallis test: χ2=
19.03, df= 2, P< 0.001). Natural threats were higher among endemic
species (Kruskal-Wallis test: χ2= 10.15, df=
2, P= 0.01). In terms of average
threats per species, Mindanao endemic has higher mean number of threats (mean=
2.00 ± 1.98) compared to non-endemic (mean= 1.41 ± 1.52) and Philippine endemic
species (mean= 1.12 ± 1.53).
Discussion
Biodiversity
assessments and monitoring provide important information to understand species
diversity and conservation (Tanalgo et al. 2015). Field data, particularly from rapid
biodiversity surveys are often undervalued, but when carefully synthesised are
useful to inform the local state of biodiversity, which aids or complement
prioritise key areas, habitats, and species (Tanalgo
et al. 2019). Mt. Hilong-hilong
interests many natural history scientists and conservation biologist within and
outside the region. Yet, most
ornithological studies and surveys that occurred are rarely published. The Philippine Eagle Foundation
pioneered the ornithological surveys on the western side of the mountain and
reported 120 species with 51% Philippines endemics (The Philippine Eagle
Foundation 2007). This was
followed by an ecological study on the effects of vegetation on birds in Mt. Hilong-hilong by Paz et al. (2013). Forty-six species were observed in San
Antonio located on the western side of the mountain (Hosner
2012). By combining past and current
survey data from Mt. Hilong-hilong, we found an
increase in recorded species and higher proportions of endemism, as other
species were not previously recorded before were pooled together, supporting
the importance of Mt. Hilong-hilong in conserving
important populations of birds in the KBA zone.
Key Biodiversity Areas are identified sites across large scale networks
by identifying areas that contain unique, vulnerable, and irreplaceable
population (Eken et al. 2004). KBA's primarily concerns to aid the
conservation and protection of population viability of highly-threatened
species or populations based on global-scale criteria (e.g., the IUCN Red List)
(Margules & Pressey
2000). Although our
analysis showed lower numbers of threatened species (N= 12 spp., 8%), we found
a higher proportion of species with declining populations (N= 79 spp., 53%) in
Mt. Hilong-hilong. Likewise, we found high
proportions of species with restricted distributions (N= 73 spp., 50% endemism
level) and this conforms to the other three criteria based on species
irreplaceability (Margules & Pressey 2000).
Key Biodiversity Areas
with relatively more intact vegetation represents an important site for
conservation safeguarding populations of bird taxa from multiple threats (Plumptre
et al. 2019). The risk of
extinction for birds in Mt. Hilong-hilong is higher
among Mindanao and Philippine endemic.
Our study found high proportions of endemic species within Mt. Hilong-hilong, and this could be associated with relatively
intact, denser and diverse vegetation of native plants within the KBA zone
particularly in the lower to mid-elevation, thus more suitable to support
wide-suit of bird species and their different life-histories. Tanalgo et al. (2019) compared different
habitats in the lowlands of south-central Mindanao and found more endemic
species in protected areas and at reforested sites with better vegetation
structure compared to more homogenised plantations and urbanised areas. Previous studies also showed that the density
and richness of endemic bird species are strongly correlated with the
vegetation intactness and structure (Mills et al. 1991; Daniels et al. 1992; Mejías & Nol 2020). Although the majority of avian species in Mt.
Hilong-hilong are considered least threatened, yet
large proportions are facing threats from direct-human threats such as hunting,
albeit there is no clear evidence detailing the extent of this threat for birds
and other wildlife in the KBA. Whereas
land-use driven threats such as deforestation and agricultural expansion remain
a key threat to 49% of species particularly those forest-dwelling species with
narrow distributions. In contrast with
other threats, deforestation and agricultural expansions led to habitat
fragmentation that may immediately influence the alterations of diversity and
composition of native species present in these systems (Bujoczek
et al. 2020; Hatfield et al. 2020; Tchoumbou et al.
2020). Declining strict forest-dwelling
species at a regional scale is widely associated with human disruption to
habitats that reduce the space occupied by and affect the foraging grounds of a
diverse set of species (Brooks et al. 1999; Renjifo
2001). Global
meta-analyses showed that bird species richness and abundance were particularly
susceptible to decline in areas with low structural heterogeneity such as
plantations and farmland conversions (Bohada-Murillo
et al. 2020). The continuous conversion
within or near intact habitats for agricultural expansions during the last
decades has driven high biodiversity loss in many hotspot regions including the
Philippines (Brooks et al. 2002). Apart
from the high diversity of forest-dwelling birds in Mt. Hilong-hilong,
we recorded at least 16 migratory species.
Intact areas (e.g., protected areas and key biodiversity areas) as
interconnected networks of conserved and protected sites are crucial for migratory
birds serving as routes supporting the full annual cycle of at least 9% of
global migratory birds (N= 1,451 spp.) (Runge et al. 2015).
We found more endemic
and threatened species in the lower elevation (0–100 m) and mid-elevations
(100–500 m) of Mt. Hilong-hilong, but this should be
taken with prudence as the sampling effort or the employed techniques per
elevation may vary. This diversity
pattern (i.e., species richness) may be explained by the vegetation structure
in relationship to elevation in the KBA.
In a previous study in Mt. Hilong-hilong, Paz et al. (2013) showed that
vegetation and elevation were key drivers affecting endemic species
distribution in the KBA. Vegetation is a
key determinant of increased species richness and diversity (Canterbury et al.
2000; Tchoumbou et al. 2020) and the effect of
elevation may negatively affect vegetation and consequently species diversity
and richness across many animal taxa including birds (Kattan
& Franco 2004; McCain 2009). In a
study in the Rwandan mountains, elevation was found to have inverse effects and
vegetation structure positively influenced bird diversity (Derhé
et al. 2020). Similarly, this pattern
was observed in the eastern Himalaya; Acharya et al. (2011) demonstrated that
intermediate elevations had the highest bird species richness, where primary
productivity was at the optimal peak.
In terms of feeding
groups, the majority of the species recorded in Mt. Hilong-hilong
are insectivorous, frugivorous, and carnivorous. Elevation has been shown to affect the
distribution of functional groups, for example, elevation strongly influences
insectivorous birds but not on frugivorous birds in tropical forest landscapes
as influenced by their varying foraging strategies across different vegetation
(i.e., more insect biomass) and climate strata (Jankowski et al. 2013; Santillán et al. 2020).
Although there was no significant relationship found between feeding
groups and elevation, species that were recorded strictly or specific in an
elevation may represent an important indicator to future monitoring of bird
response to habitat system within Mt. Hilong-hilong. Species feeding guild can indicate habitat
structure or quality for species to persist.
A study comparing a protected area with an agricultural area in
Serengeti showed that at least 50% of insectivorous and granivorous birds found
in forests were absent in agriculture, suggesting that more intact ecosystems
can safeguard a large proportion of specialist species (O’Connell et al. 2000;
Sinclair et al. 2002). In a similar
study, bird functional diversity depended on the overall habitat types (Tanalgo
et al. 2019), and the intactness of forest, in which species
responded negatively to disturbance gradient, for example, omnivores,
insectivores and frugivores were lowest in numbers in areas with selective
logging and plantation conversions within a tropical rainforest (Tchoumbou
et al. 2020). The
intactness of KBAs strongly relies on the physical features (e.g., landscape
structure), presence of threats, and changes in land-use (Rayner et al. 2014). To circumvent these threats, protected areas
and other forms of designated sites serve as a chief tool optimising the
conservation and protection of many species (Butchart et al.
2015). Conservation
initiatives such as the establishments of KBAs allows the identification of
important areas for protection (i.e., the establishment of protected areas)
from human alteration. Yet, the
identification of KBAs alone is not sufficient to ensure the protection of its
ecosystems and important taxa; it requires effective monitoring of its
biodiversity and the extent of the potential threatening process (Beresford et
al. 2020). To optimise the role of KBA
to safeguard critical habitats and their biodiversity it should be primarily
protected first by the statutory policy.
In conclusion, our
synthesis demonstrated the presence of high diversity of endemic and threatened
bird species in Mt. Hilong-hilong harbour, and the
vital role of the KBA as an important habitat for bird conservation and
protection. Our study exhibited that
local biodiversity could be effectively understood by integrating findings from
multiple datasets, particularly those from rapid surveys and assessments (Fig.
5) (Tanalgo et al. 2019). Here, we acknowledge that our findings were
based on the synthesis of the different dataset that employed varying sampling
methods and approach (e.g., intensity and effort, taxonomic identification)
that may have affect the robustness of data (Manu & Cresswell 2007) thus, careful interpretation is
required. Yet these caveats warrant more
intensive efforts and opportunities to produce robust data across elevational
and vegetation gradient to fully elucidate their relationship to species
diversity and other ecological indicator groups.
The rapidly changing
environment and the growing development outside and the lowlands of KBA where
habitat change is likely to occur and could pose important attention and
concerns for conservation. For instance,
from 2002–2019 at least 4.66Kha of humid primary forest was lost within the KBA
zone, which most likely caused by deforestation and shifting agriculture (Global Forest Watch
2020). In addition
to land-use changes, direct human impacts to birds such as hunting in the KBA
may pose another threat to many populations.
These threatening processes will likely affect many species particularly
larger species (e.g., large-fruit doves) and those with narrow distributions (Tanalgo 2017). Thus
future studies must aim to understand and explore the extent and impacts of
these threats to species in Mt. Hilong-hilong. Future conservation priorities should
advocate more protection of endemic species which more tends to be threatened
in Mt. Hilong-hilong.
Furthermore, we demonstrate here that collaborative efforts may promote
effectual conservation by combining different data from different survey
efforts that often remain in grey literature, enable biodiversity synthesis by
increasing relevant information to better understand species diversity (Tanalgo
et al. 2019). Bolstering
efforts promoting transparent and collaborative science-based conservation
intervention is central to better complement and sustain existing conservation
management not only in Mt. Hilong-hilong (Mohagan et al. 2015;
Amoroso et al. 2018) but across all other important biodiversity sites in the
country (Fig. 5).
Table 1. Diversity
summary of birds in Mt. Hilong-hilong in terms
species richness according to feeding guild, endemism, movement pattern,
conservation status, and population status. See Supplementary Data 1 for full
list of species listed and analysed in the study https://doi.org/10.6084/m9.figshare.13168916.v1
Diversity
attributes |
Number of species |
% |
Record from new
field survey |
Feeding guild |
|
|
|
Carnivores |
18 |
12 |
10 |
Frugivores |
28 |
19 |
18 |
Granivores |
5 |
3 |
2 |
Insectivores |
73 |
49 |
41 |
Nectarivores |
15 |
10 |
9 |
Omnivores |
9 |
6 |
2 |
Endemism |
|
|
|
Non endemic |
75 |
51 |
39 |
Philippine Endemic |
53 |
36 |
35 |
Mindanao Endemic |
20 |
14 |
8 |
Migration Pattern |
|
|
|
Full Migrant |
16 |
11 |
10 |
Non migrant |
132 |
89 |
72 |
Conservation status |
|
|
|
Data Deficient |
1 |
1 |
0 |
Least Concern |
124 |
84 |
71 |
Near Threatened |
11 |
7 |
4 |
Vulnerable |
11 |
7 |
7 |
Endangered |
1 |
1 |
0 |
Population status |
|
|
|
Decreasing |
79 |
53 |
43 |
Increasing |
5 |
3 |
4 |
Stable |
60 |
41 |
33 |
Unknown |
4 |
3 |
2 |
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