Justification of Red List category
This species is listed as Endangered because it has a very small population which is undergoing continuing declines owing to overexploitation and loss and degradation of its wetland habitats (Collar and Stuart 1985).
Survey data from 2003 and 2004 combined with past literature suggests that there are no more than 1,500 individuals, roughly equivalent to 1,000 mature individuals.
This species's population is suspected to be decreasing in line with levels of egg-collection and hunting, cutting of nesting-trees, conversion of remaining wetlands to rice-paddies, and siltation of wetlands as a result of watershed deforestation. The likely rate of population decline, however, has not been estimated.
Ardea humbloti breeds only in Madagascar but is also recorded as a vagrant from the Comoro Islands and Mayotte (to France). In 1973, it was reported to have declined alarmingly and to be facing extinction unless completely protected. More recently it was found to be fairly common (though patchily distributed) in parts of north and west Madagascar, and uncommon in the south (Langrand 1990), with occasional records in the central highlands and east of Madagascar (Safford and Hawkins 2013). It has also been seen regularly at Lake Alaotra (ZICOMA 1999), and is found offshore in the Anorontany archipelago (Rahaerilalao 2010). The total population was recently estimated to number 1,000-3,000 individuals (F. Hawkins in litt. to Wetlands International 2002), although since then survey data from 2003 and 2004 combined with past literature has resulted in an estimation of no more than 1,500 individuals (Andrianarimisa et al. in press). It is now judged to be restricted to western Madagascar, where it is sparsely distributed, with its stronghold being the Antsalova region (Andrianarimisa et al. in press).
Behaviour There is no evidence of migration in this species, but it is prone to long-distance wandering in search of suitable habitat (Hancock and Kushlan 1984, Kushlan and Hancock 2005). It is usually seen alone, sometimes with other herons (Langrand 1990). It breeds mainly in small groups of a few pairs in mixed species colonies but also solitarily (Langrand 1990, del Hoyo et al. 1992, Koenig 2012). Various independent observations suggest that nesting takes place year-round (Langrand 1990, ZICOMA 1999, Andrianarimisa et al. in press). There are observations of Grey Heron Ardea cinerea and A. humbloti chicks occupying the same nests; though there is no evidence of mixed pairings or hybridisation, and this interaction between the two species is not understood (Andrianarimisa et al. in press). Habitat The species prefers coastal areas (including coral islets, mangroves, tidal mud flats and estuaries) (Hancock and Elliott 1978, Kushlan and Hancock 2005), but also frequents freshwater lakes (particularly those that persist through the dry season and are in close proximity to other lakes [Andrianarimisa et al. in press]), rivers and, more rarely, rice-paddies (Hancock and Elliott 1978, Kushlan and Hancock 2005). It forages in clear, shallow waters (Hancock and Elliott 1978, Langrand 1990) and among floating vegetation (Hancock and Elliott 1978, del Hoyo et al. 1992). Habitat suitability depends on water clarity, shoreline areas with shallow water and the availability of large fish (Andrianarimisa et al. in press). Diet It feeds chiefly on medium to large fish (up to 20 cm [del Hoyo et al. 1992]) and crustaceans (Langrand 1990, Morris and Hawkins 1998). Breeding Site It nests in tree-tops or hollows in rocks, and has also been reported to nest on the ground (Hancock and Kushlan 1984, Kushlan and Hancock 2005). Breeding may occur throughout the year, and breeding success is probably low (Safford and Hawkins 2013). Clutch size is three.
Natural wetlands have been degraded by modification and conversion for human use, particularly for rice cultivation (Stattersfield et al. 1998, Andrianarimisa et al. in press), and by siltation as a result of watershed deforestation (Stattersfield et al. 1998). The former wetlands of the central highlands may once have been important refuges for immature birds (Andrianarimisa et al. in press). At the nest it is especially vulnerable to disturbance, egg-collection and the capture of nestlings by local villagers for food (ZICOMA 1999, Andrianarimisa et al. in press). These pressures are likely to reduce its numbers as the human population of western Madagascar continues to increase (ZICOMA 1999), however the establishment of a local community association resource management process (Gestion Local Securisee or GELOSE) has significantly decreased these activities in these zones (Razafimanjato et al. 2007). Cutting of nesting-trees can also be a significant threat, e.g. at Manambolomaty Ramsar Site where this has caused an alarming decline over the last 10 years (ZICOMA 1999). Wetlands in Madagascar have long been in decline as the climate has become progressively drier (Stattersfield et al. 1998), and this has been compounded by the degradation of wetlands (Stattersfield et al. 1998). The depletion of fish stocks by local fisheries is a potential threat (Andrianarimisa et al. in press).
Conservation Actions Underway
This species is recorded from Ankarafantsika Strict Reserve, Ankarana Special Reserve and Baly Bay National Park, but overall its habitat is poorly protected (Langrand 1990), with c.50% of the population residing outside protected areas (Andrianarimisa et al. in press). The Malagasy government has ratified the Ramsar Convention, which came into force for the country in 1999, and this may herald improved conservation measures for wetlands. During surveys in the Antsalova region in 2003/2004, the numbers of this species, on average for each site, were found to be significantly higher on lakes in designated Ramsar Sites (lakes Befotaka, Soamalipo, Ankerika and Antsamaka) compared with lakes outsite designated sites (Andrianarimisa et al. in press). However, this could be due to variations in survey effort, the availability of suitable shoreline habitat, the proximity of the relatively undisturbed Tsimembo Forest, which prevents serious soil erosion, or the proximity of lakes to one another (Andrianarimisa et al. in press). A survey in 1999 found the species in 20 Important Bird Areas within the West Malagasy Endemic Bird Area (ZICOMA 1999).
100 cm. Large, solitary heron. Upperparts mostly mid-grey, with darker cap, cheeks and flight feathers. Massive, pale straw-coloured bill, tending to orange in breeding season. Paler grey underparts, pale flesh or greyish legs and feet. Similar spp. From Grey Heron A. cinerea and Purple Heron A. purpurea by solid dark cap, uniform grey plumage lacking white or rufous, and more massive bill. Hints Often on mudflats adjacent to mangroves, or on fringes of large lakes.
Text account compilers
Ekstrom, J., Evans, M., Khwaja, N., Martin, R, Pilgrim, J., Shutes, S., Starkey, M., Symes, A., Taylor, J., Westrip, J.
Rabenandrasana, M., Andrianarimisa, A., Hawkins, F., Langrand, O.
BirdLife International (2023) Species factsheet: Ardea humbloti. Downloaded from http://datazone.birdlife.org/species/factsheet/madagascar-heron-ardea-humbloti on 10/12/2023.
Recommended citation for factsheets for more than one species: BirdLife International (2023) IUCN Red List for birds. Downloaded from http://datazone.birdlife.org on 10/12/2023.