Alaotra Grebe (Tachybaptus rufolavatus)
Posted on 31 December, 1985 in Extinct
Year Last Seen:
1985
Comments:
Thorough surveys of Lake Alaotra in 1989, and further surveys in 2004 and 2009 failed to find any evidence of the species. Multiple methods for determining the likelihood of extinction have used the sighting history of this species as a test dataset and each has determined that the species is extinct beyond reasonable doubt. The probability of the species being extinct from these models first exceeded 95% during the period between 1989 and the start of 2005. Separately, an expert-led assessment of the probability of extinction based on the severity and spatial extent of threats concluded there was 90% probability that it was extinct. Considering the last confirmed sighting of the species was in 1985 despite adequate survey of remaining habitat within the potential range, and in view of the threats to the species, its lack of mobility and restricted range, this species is considered to be Extinct.
Habitat:
Behaviour This species was presumed to be strongly sedentary since its small wings render it unable to fly long distances. Some movements to highland lakes and ponds other than Lake Alaotra were thought to have occurred as a result of the degradation of its preferred habitat, as opposed to representing habitual movement (del Hoyo et al. 1992). It was usually found in pairs, sometimes in association with T. ruficollis (Langrand 1990). It was thought to have a flexible breeding season, with historical records of breeding in April-June and in January-March (del Hoyo et al. 1992). Habitat Lake Alaotra is a large, shallow, brackish lake. Its shores were historically covered with dense vegetation including papyrus and reeds, which may have been important for this species (del Hoyo et al. 1992). Diet It fed almost exclusively on fish (Langrand 1990). Breeding site Nothing was known of its breeding ecology (Langrand 1990).
Causes:
Several major factors contributed to this species' extinction. The primary driver of the rapid population reduction and loss of most individuals is considered to be the introduction of the carnivorous fish Micropterus salmoides and Channa striata (ZICOMA 1999), which caused adult mortality but more significantly reduced reproduction to near-zero. These fish were introduced to the Alaotra basin in the 1950s and very rapid population declines appear to have commenced shortly afterwards. Additional introductions of exotic plants, mammals and fish, especially Tilapia, probably depleted essential foods for the species (Pidgeon 1996). Conversion of natural habitat for agriculture also occurred at an increasing rate during this time, with deforestation resulting in sedimentation from soil erosion and water quality being lowered, and considerable area has been converted to rice farms (Wilmé 1994). The use of monofilament nylon gill-nets at Lake Alaotra proliferated more recently, to the extent that they now cover a large part of the open lake. They undoubtedly kill many diving waterbirds; however the introduction of this fishing method probably only happened after the grebe had already been greatly reduced in number or had disappeared (Hawkins et al. 2000). The final few individuals may have been lost through hybridisation with T. ruficollis, although this appears to have been occurring for a long time as the type series from 1932 includes a presumed hybrid (Delacour 1932, Collar and Stuart 1985, Hawkins et al. 2000). Poaching may also have played a role in the extinction of the species (Wilmé 1994), although larger-bodied waterbirds are thought to have always been the primary target of hunters (Hawkins et al. 2000).
Distribution:
Tachybaptus rufolavatus was endemic to Madagascar and known chiefly from Lake Alaotra (ZICOMA 1999). There have been no confirmed sightings since 1985 when two were seen (in addition to several apparent hybrids) near Andreba on Lake Alaotra in September 1985 (Hawkins et al. 2000, P. Thompson in litt. 2022). After this an adult and an immature were reported as the species in 1986 (B. Dawson, unpublished report) and two individuals (also an adult and an immature) which may have been Alaotra Grebe were again reported in 1988 (D. Thorn, unpublished report) but these were not documented and may have been hybrids (Hawkins et al. 2000). Survey visits to Lake Alaotra in 1989-90 (Young and Smith 1989, Wilmé 1994) 1993 and 1994 (Pidgeon 1996), then 1997-1999 failed to produce any sightings, prompting a targeted survey in 1999 which only located four T. pelzelnii (ZICOMA 1999, Hawkins et al. 2000). Visits in 2000 found no individuals (of this or any species of Tachybaptus) on Lake Alaotra or surrounding lakes, and further surveys drew blanks in 2004 and 2009 (H. G. Young in litt. 2009). Records outside the Lake Alaotra region were unreliable as species was probably incapable of prolonged flight, so in all likelihood never occurred very far from Lake Alaotra (ZICOMA 1999, Hawkins et al. 2000). Checks of additional potential sites, in particular Lake Amparihinandriamabavy (F. Hawkins in litt. 2009), have failed to find any grebes. It is now considered extinct, as no suitable wetlands remain unsurveyed in the Alaotra region (H. G. Young in litt. 2009).