Justification of Red List Category
This species is listed as Endangered because it has a very small population which is undergoing a continuing decline due to the ongoing degradation of its wetland habitats and the exploitation of its eggs and young.
The population size was estimated to be 531 breeding pairs in 2016, based on surveys, densities, and areas of potential suitable breeding locations (Rabarisoa et al. 2020). This would roughly equate to 1,062 mature individuals. GEPOMAY (2019) surveyed nearly 200 pairs on Mayotte, and based on Mayotte containing 20% of the breeding population, estimated the number of global pairs at c.1,000, equivalent to 2,000 mature individuals. The population size is therefore placed in the band 1,000-2,499 mature individuals.
This species is inferred to be declining due to ongoing wetland habitat loss and degradation (Kull 2012; D'Urban Jackson et al. 2019). Surveys and census reviews by Rabarisoa et al. (2020) found that the two largest and oldest breeding colonies on Madagascar had declined by c.53% and c.41% between 1993-2016, in addition to the disappearance of previous breeding sites on both Madagascar and Aldabra. The trend of the breeding population on Mayotte may be increasing (Rocamora 2004 in Ndang’ang’a and Sande 2008), however the increase may also be due to improved monitoring efforts (Jeanne et al. 2015 in Rabarisoa et al. 2020). The overall rate of population decline is suspected to fall in the band of 30-49%.
Ardeola idae breeds on Madagascar (Once 2,000-6,000 individuals [Delany and Scott 2002]), Aldabra (20-50 pairs in 2001 [Ndang’ang’a and Sande 2008] down from 100 breeding pairs in 1970 [Benson and Penny 1971]) in the Seychelles, Mayotte (to France) (once 10-20 pairs [Rocamora, 2004; Rocamora & Said, 2008], now c.200 pairs c.2019 [GEPOMAY 2019]) and Europa (15 pairs [Ndang’ang’a and Sande 2008] (Réunion, to France). It has a large non-breeding range in Central and East Africa including the Comoro Islands, Mozambique, Zimbabwe, Zambia, Malawi, Tanzania, Kenya, Uganda, Burundi, Rwanda and Democratic Republic of Congo. It is present almost throughout Madagascar, but is always uncommon (ZICOMA 1999). It is rare in the south and probably commonest in suitable wetlands in the west (Morris and Hawkins 1998). A decline has been reported over the last 50 years, most notably on the high plateau (Salvan 1970, 1971, 1972, Morris and Hawkins 1998), although the Mayotte population appears to be increasing (Rabarisoa et al. 2020). Whilst it remains fairly widespread, populations are low, and increasing exploitation at most breeding sites is likely to increase the rate of population decline (ZICOMA 1999).
Behaviour This species is migratory (del Hoyo et al. 1992). It breeds between October and March with a peak at the start of the wet season in November and December (del Hoyo et al. 1992). Breeding is colonial, the species occurring historically in groups of up to 1,000 pairs (del Hoyo et al. 1992, Kushlan and Hancock 2005), though now usually in much smaller numbers (Burger 1990), often as part of mixed-species colonies (Burger 1990, del Hoyo et al. 1992, Kushlan and Hancock 2005). It migrates westward in May, and returns to its breeding range in October (del Hoyo et al. 1992, Kushlan and Hancock 2005). On Mayotte, part of the breeding population does not appear to migrate (GEPOMAY in litt. 2020). First-year birds are reported to remain in the non-breeding areas during the breeding season (del Hoyo et al. 1992). It forages solitarily. Habitat It principally inhabits freshwater wetlands, particularly shallow waterbodies fringed with vegetation and adjacent trees (del Hoyo et al. 1992). Breeding In its Madagascan breeding range it occurs in grassy marshes, small lakes, ponds, ditches and rice fields, usually near trees and bushes (Kushlan and Hancock 2005), although it has been recorded nesting on islands where trees are scarce (Burger 1990). On Aldabra it uses mangroves, shallow inland pools and lagoon shores (Kushlan and Hancock 2005, Bunbury 2014), and is occasionally found to inhabit areas away from water (Benson and Penny 1971). On Mayotte they feed around lakes, rivers (even in forests) and wetlands (GEPOMAY in litt. 2020). Non-breeding In its non-breeding range it is commonly found along the banks of small streams, including those inside forest. It is also found on rice paddies, and more rarely in mangroves and on the seashore (Kushlan and Hancock 2005). Diet It feeds on fish, insects and small invertebrates (Morris and Hawkins 1998), as well as frogs and small reptiles including skinks (Scincidae) and geckos (Gekkonidae) (Kushlan and Hancock 2005). Breeding Site It nests in trees and bushes in or near to marshes, lakes or ponds (del Hoyo et al. 1992, Kushlan and Hancock 2005). On Aldabra it also nests in mangroves (Kushlan and Hancock 2005). On Mayotte they nest in colonies in mangrove forests with cattle egrets Bubulcus ibis (Rocamora & Said 2008). The nest is bulky and constructed of twigs (del Hoyo et al. 1992, Kushlan and Hancock 2005). In Madagascar, it tends to be placed 0.5-4 m above the ground (del Hoyo et al. 1992), and when the species occurs in a mixed colony with A. ralloides, it occupies the higher nesting sites (del Hoyo et al. 1992). In Mayotte, nests tend to be placed up to 12m above the ground (E. Dautrey in litt. 2020). Typical clutch size is 3, incubation lasts about 20 days and chicks can feed alone at under 4 weeks old (Kushlan and Hancock 2005).
The principal threat for this species is thought to be habitat loss as a result of the clearing, drainage and conversion of wetland habitats to rice fields (Kushlan and Hancock 2005). The main threats to this species at its nesting sites are the collection of eggs and fledgling birds, and human disturbance (Rabarisoa et al. 2020). Human disturbance and harvesting of eggs and chicks has been reported in both the Madagascar and Mayotte colonies (G. Rocamora in litt. 2020). Despite the establishment of a local community association resource management process (Gestion Local Securisee or GELOSE) (Razafimanjato et al. 2007), these threats were present at 73% of the 11 known nesting sites c.2016 (Rabarisoa et al. 2020). Further threats of predation and swamp fires were found at 23% of nesting sites (Rabarisoa et al. 2020).The introduced fish Micropterus salmoides may compete for food (Salvan 1971, 1972). There is also evidence of hybridisation with Squacco Heron Ardeola ralloides on Madagascar (Ndang’ang’a and Sande 2008). Predation of eggs and young chicks by invasive rats may also be a problem (G. Rocamora in litt. 2020).
Conservation Actions Underway
CMS Appendix II. Madagascar has ratified the Ramsar Convention, which should increase the priority given to wetland conservation. Forthcoming conservation efforts will focus on freshwater wetlands in Madagascar (R. Safford in litt. 2003), and actions have been proposed for Mayotte (GEPOMAY 2012), and were being developed and implemented in 2019 (Rabarisoa et al. 2020), including a French National Action Plan for 2019-2023 (Jeanne et al. 2018). The species is fully protected on Aldabra Atoll (N. Bunbury in litt. 2016).
45-48 cm. Small white heron. Breeding plumage all white, with long crest and scapular plumes. Blue bill and bare orbital skin, former with dark tip. Reddish legs. In non-breeding plumage, dark brown on crown and streaked dark brownish on mantle and underparts. Similar spp. In breeding plumage, easily distinguished from other white herons by short reddish legs and blue bill. In non-breeding plumage, from Squacco Heron A. ralloides by dark crown and streaky upperparts. Hints Found singly or in small groups, often with A. ralloides or egrets. Nests colonially with other herons.
Text account compilers
Benstead, P., Bunbury, N., Dautrey, E., Ekstrom, J., Evans, M., Hawkins, F., Khwaja, N., Martin, R., Pilgrim, J., Robertson, P., Rocamora, G., Safford, R., Starkey, M., Symes, A., Taylor, J. & Westrip, J.R.S.
BirdLife International (2022) Species factsheet: Ardeola idae. Downloaded from http://www.birdlife.org on 02/07/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 02/07/2022.