VU
Malabar Grey Hornbill Ocyceros griseus



Justification

Justification of Red List Category
The species is inferred to be declining at a rapid rate based on two independent sources; a significant decline in densities recorded from targeted surveys conducted in 2004-5 and 2017-18; and declining abundance indices from citizen science data collected throughout the range. The cause of these reductions are unclear. As such, Malabar Grey Hornbill is assessed as Vulnerable under Criterion A2bc + A3bc + A4bc.

Population justification
The overall global population size has not been quantified, but the species is a generally common and widely distributed species along the Western Ghats, most frequent at mid-elevations (Mudappa and Raman 2009). Highest densities were found in Reserved Forests, but the species was frequent throughout, especially in moist forest. However, recent population estimates and indices in comparison with available historical data suggest a significant and rapid decline, both locally and range-wide (D. Mudappa and T. R. S. Raman in litt. 2020).

During 2004-5, biologists estimated relative abundance (Balasubramanian et al. 2004) and population density (Mudappa and Raman 2009) from number of wildlife along the Western Ghats (Balasubramanian et al. 2004, Mudappa and Raman 2009). Significant populations were reported in moist forest habitats and mid-elevations (600-1100 m) in Agasthyamalai and Anamalai Hills, and the Periyar landscape in the southern Western Ghats (Mudappa and Raman 2009). Density estimates from a more northern location in Anshi – Dandeli – Goa landscape (9.4 individuals/km², 95% Confidence Interval = 6.1 – 14.4) were lower than in the southern Western Ghats (Mudappa and Raman 2009). 

In the Anamalai – Parambikulam landscape of the southern Western Ghats, line transect surveys during 2004-5 estimated a mean density of Malabar Grey Hornbills of 67.4 individuals/km² (95% CI =40.4 – 94.4 individuals/km²) in Reserved Forests, 28.5 individuals/km² (CI = 23.9 – 33.1) in Wildlife Sanctuaries (now Tiger Reserves), and 26.0 individuals/km² (CI = 18.6 – 33.4) in rainforest fragments on the Valparai Plateau (Mudappa and Raman 2009). Within the Anamalai Tiger Reserve, the mean density of Malabar Grey Hornbill was higher in three sites at middle elevations (700–1,000 m): Anaigundi Shola (42.7 individuals/km²), Karian Shola (48.7 individuals/km²), and Varagaliar–Manamboli–Sheikalmudi complex (40.8 individuals/km²), and broadly similar across rainforest fragments within plantations on the Valparai Plateau (21.5–33.5 individuals/km²) according to Mudappa and Raman (2009).  

Comparable estimates for the Anamalai landscape from 2017-8 (P. Pawar, D. Mudappa, and T. R. S. Raman in litt. 2020), indicate a 39% decline in population density inside the protected area (to 17.5 individuals/km², CI = 12.8-23.9) and a 55% decline in the Valparai Plateau (to 11.7 individuals/km², CI = 7.1-19.3). 

Range-wide population trend using abundance indices generated from eBird data also indicates considerable declines (SoIB 2020). The report estimates -66.8% (95% CI = -43.6 to -89.9%) long-term decline and -3.3% annual decline between 2014-2018 for the species, although the wide confidence intervals meant that the species was placed in the Moderate Concern category rather than High Concern (SoIB 2020). Supplementary temporal data for Malabar Grey Hornbill provided by the authors of SoIB (2020), indicates a higher confidence in the recent data, for which an extrapolation to three generations would be a 42% decline.

Trend justification

Recent density estimates and indices in comparison with available historical data suggest a significant and rapid decline, both locally and range-wide. Information provided to the IUCN SSC Hornbill Specialist Group (P. Pawar, D. Mudappa & T. R. S. Raman unpublished data) shows a reduction in mean population densities of 39% within the protected area and a decline of 55% in resurveyed forest fragments outside of protected areas. 

Independently, range-wide abundance indices calculated from eBird data also indicate a rapid population reduction in recent years (SoIB 2020). Wide confidence intervals and separate concerns over the type of data included in the long-term trend assessment for the species meant the species was not considered of High Concern, however the current trend between 2014-2018 also suggest a rapid decline, the mean of which is 3.3% annually, which equates to an exponential decline rate of 42% over three generations (16.5 years: Bird et al. 2020). 

Taken together, there is sufficient evidence to infer that there is a rapid ongoing population reduction across the range at a rate of 30-49% over three generations. This is believed likely to continue unless the critical factors driving the decline are identified and reversed.

Distribution and population

The species is endemic to the Western Ghats of India, from about Nashik in the north to the southernmost hills (Ali and Ripley 1983, eBird 2020). The species occurs from an elevation of about about 50 m above mean sea level near the coast (e.g., Phansad Wildlife Sanctuary, Maharashtra) to around 1,500 m in the mountains (Mudappa and Raman 2009). In the southern Western Ghats, Raman and Mudappa (2003) reported that Malabar Grey Hornbills were seen in evergreen forests between 500 m and 900 m (sporadically to 1,100 m) elevation in Kalakad – Mundanthurai Tiger Reserve, but frequently up to 1,200 m in the Anamalai Hills further north. In both sites, the estimated Malabar Grey Hornbill density decreased with elevation, with the density in rainforest fragments in the Anamalai Hills being additionally positively related to food tree species richness (Raman and Mudappa 2003).

Ecology

It is common in the tropical wet evergreen forests and moist forests of the Western Ghats (Balasubramanian et al. 2004, Mudappa and Raman 2009). Within the moist forest tracts, it also occurs in home gardens, timber plantations, shade coffee and cardamom plantations, particularly where they adjoin forests (Raman 2006, Sidhu et al. 2010). 

The breeding season extends from February to May in the Nilgiris and Anamalai Hills, Western Ghats (Mudappa 2000, Maheswaran 2002). In tropical wet evergreen forests of the Anamalai Hills, the hornbill was recorded nesting in 13 tree species such as Alseodaphne semecarpifolia, Hopea parviflora, Aglaia roxbhurghiana, Artocarpus sp., and Mimusops elengi, selecting nest trees of significantly larger diameter at breast height (DBH 60-89 cm), and greater height of the lowest branch than random trees (Mudappa and Kannan 1997, Mudappa 1998).Tropical semi-evergreen forest of Mudumalai Wildlife Sanctuary, nests were located in 19 tree species (over two-thirds of the nests were in Lagerstroemia microcarpa, Terminalia bellirica and T. crenulata) and in large trees (mean height = 36 ± 6 m, girth at breast height = 3 ± 1 m, nest height = 17 ± 6 m; Balasubramanian and Maheswaran [2002], Maheswaran & Balasubramanian [2003]).  Nests were also observed in non-native trees like Eucalyptus and Grevillea. A clutch of 4 eggs are laid. Incubation period is about 40 days and fledgling period is 46 days (Mudappa 2000). About 5% of the nests were reported to become annually defunct due to change in nest entrance, fire, treefall etc. (Mudappa 2005). Fruits of liana species (and some shrubs), especially species in the plant families Lauraceae, Moraceae, Annonaceae, and Euphorbiaceae are consumed during breeding and non-breeding season (Mudappa 2000, Balasubramanian and Maheswaran 2002). This species also consumed animal matter during the breeding season (Mudappa 2000). Large flocks (up to 20) are sometimes noticed in coffee plantations, where shade trees such as Ficus spp. and  Maesopsis emenii (non-native) offer fruits consumed by the hornbills.

Threats

Deforestation driven by agricultural conversion in the northern part of the range is thought to be driving some declines in the species's population in this region (Kemp and Boesman 2019, Mudappa and Raman 2020), and the availability of large trees with suitable nesting cavities may be limiting (Mudappa and Raman 2020). Fragmentation of forest also affects the species (Raman and Mudappa 2003).

However, declines in density have occurred within protected areas, where there does not appear to have been a significant habitat change, which indicates that further research is required to identify plausible drivers of the decline. Potential threats may come from an undocumented shift in range for a competitor or predator, undetected disease affecting either the individuals of this species or limiting resources, or changed agricultural practice with an as yet undocumented impact on the species.

Conservation actions

Conservation Actions Underway
Occurs in multiple protected areas throughout the Western Ghats. Listed as an endangered species under Schedule 1 of India's Wildlife Protection Act of 1972. 

Conservation Actions Proposed
Research into species-specific drivers of recorded decline. Ensure compliance with forest protection regulations within protected areas, to prevent loss of large trees with suitable cavities, or large trees that will develop large cavities.  Assess the adequacy of remote sensed data for detecting relevant habitat degradation/loss for this species. Consider whether there is benefit to the provision of artificial cavities to reduce resource limitation among the suite of species that require them.

Acknowledgements

Text account compilers
Datta, A., Patil, I., Martin, R.

Contributors
Mudappa, D., Raman, T.R.S., Pawar, P. & Balasubramanian, P.


Recommended citation
BirdLife International (2021) Species factsheet: Ocyceros griseus. Downloaded from http://www.birdlife.org on 07/03/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/03/2021.