VU
Clarion Wren Troglodytes tanneri



Justification

Justification of Red List category
This species qualifies as Vulnerable owing to its very small population and range, and hence its susceptibility to invasion by a mammalian predator or severe damage from wildfires or hurricanes.

Population justification
The population is estimated to number 170-200 pairs, or 340-400 mature individuals and the species is apparently common throughout all of the island and around the naval garrison. According to recent data (Ortiz-Alcaraz et al. 2018), density estimates are 3.2 individuals/ha in the wet season and 6.55 individuals/ha in the dry season. Further population studies are needed.

Trend justification
There are recent counts but no new data on population trends. The introduced mammal that remains on Clarión is the European Rabbit and no evidence of negative impacts exists, aside from greatly slowing vegetation regrowth after a significant fire in the 1980s. Therefore, the population is currently suspected to be stable, although this warrants further investigation.

Distribution and population

Troglodytes tanneri is endemic to Isla Clarión in the Revillagigedo Archipelago, Mexico. Only 20 individuals were recorded in 1986 (Everett 1988), but subsequent visits to the island have found the species to be common (Howell and Webb 1989, Santaella and Sada 1991, Wanless et al. 2009). The population was estimated at 170-200 pairs in 1988, with the highest densities around buildings and adjacent areas (Howell and Webb 1989), apparently associated with Karwinskia shrub areas (Ortiz-Alcaraz et al. 2018).

Ecology

It occurs in all habitats throughout the island from rocks on the beach to shrubbery at the highest elevations (Santaella and Sada 1991). Numbers seem to be higher in areas of Karwinskia shrubs. No variability across altitudinal gradients was identified (Ortiz-Alcaraz et al. 2018). Nests are built in bushes, cacti, buildings and derelict vehicles, and one nest has been recorded to contain 4 eggs (Santaella and Sada 1991, Howell and Webb 1995, Sosa-López et al. 2012).

Threats

Introduced herbivores have extensively modified the native vegetation on Clarión (Stattersfield et al. 1998), but this has not had an impact upon this species. However, introduced rabbits Oryctolagus cuniculus may subsidise native predators, such as Burrowing Owl Athene cunicularia and Clarión Racer (Masticuophis anthony) and increase their impact on wren populations. The introduction of a mammalian predator would have extremely serious consequences. The possibility of a cat introduction is small, but mouse or rat introductions are more likely (B. Tershy in litt. 1999), and there is no active introduction prevention plan in place (B. Tershy and B. Keitt in litt. 2007). Fire is another significant threat; in 1984, a large fire burnt three quarters of the island, impacting nesting habitat with vegetation recovery extremely slow due to introduced rabbits feeding on regrowth (CONANP 2004). Furthermore, high hurricane incidence could be a potential threat for this bird as an indirect effect of climate change; strong hurricanes occur during ENSO events as a result of high sea-surface temperatures and Clarión lies on this storm track (CONANP 2004, DOF 2017). As oceanographic conditions evolve under a warming climate, winds and heavy rains will likely become increasingly frequent and intense. impacting T. tanneri nesting and individuals.

Conservation actions

Conservation Actions Underway
The Revillagigedo Archipelago was declared a biosphere reserve in 1994 (Stattersfield et al. 1998). There is a plan to eradicate introduced herbivores from Clarión; pigs and sheep have already been eradicated but rabbits remain (B. Tershy in litt. 1999, Wanless et al. 2009, Aguirre-Muñoz et al. 2018). The National Commission of Natural Protected Areas (CONANP) and the Mexican navy restricts access to the island and helps to prevent further introductions by implementing and enforcing a Biosecurity Plan (B. Tershy in litt. 1999, B. Tershy and B. Keitt in litt. 2007, Méndez-Sánchez et al. 2018). It is on the watch list as part of the State of North America's Birds (North American Bird Conservation Initiative 2016) and is listed as a species under special protection by the Mexican Official Standard, NOM-059-SEMARNAT-2010 (DOF 2010). In 2016, the Revillagigedo Archipelago was included in UNESCO’s World Heritage List as a Natural Site. This encouraged the Mexican government to take bold conservation measures to preserve the archipelago and, in November 2017, the Revillagigedo National Park was created (DOF 2017) whilst the Biosecurity Plan is ongoing (Méndez-Sánchez et al. 2018).

Conservation Actions Proposed
Carry out surveys to obtain an up-to-date population estimate. Monitor population trends through regular surveys. Eradicate introduced rabbits from Clarión and evaluate the impact of native predators like the Clarión racer and Clarión raven. Continue implementing the Biosecurity Plan to prevent the introduction of mammalian predators.

Identification

13 cm. Plain, grey-brown wren. Buff supercilium and eye-ring. Dark barring on tail and wings. Pale buff underparts, barred darker on undertail. Voice Long, dry insect-like rattle. Also chattering and tchek notes. Song similar to House Wren T. aedon.

Acknowledgements

Text account compilers
Everest, J.

Contributors
Bedolla, Y., Capper, D., Isherwood, I., Keitt, B., Mahood, S., Ortiz-Alcaraz, A., Pople, R., Sharpe, C.J., Solis-Carlos, F., Tershy, B. & Westrip, J.R.S.


Recommended citation
BirdLife International (2024) Species factsheet: Troglodytes tanneri. Downloaded from https://datazone.birdlife.org/species/factsheet/clarion-wren-troglodytes-tanneri on 01/03/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from https://datazone.birdlife.org on 01/03/2024.