VU
Green Warbler-finch Certhidea olivacea



Justification

Justification of Red List Category
This species has a small range, with available habitat at least declining in quality because of invasive plants and anthropogenic habitat alteration. The species could also potentially be impacted by other invasives, and as such the species is considered to be undergoing a rapid decline. Therefore, it is listed as Vulnerable.

Population justification
The species has been described as 'common and widespread' (Jaramillo and Christie 2017). Dvorak et al. (2012) estimated the number of singing males at 55,500 (37,300-80,600) on Santa Cruz alone.

Trend justification
Dvorak et al. (2012) compared measures of abundance (in terms of number of individuals sighted per point during point count observations) between 2008-2010 and 1997-1998. Combining the per point observations of this species for each time period and looking at an overall average for both 1997-1998 and 2008-2010 suggests that between the two survey periods (which roughly equates to 3 generations lengths [c.11.5 years]), C. olivacea potentially declined by c.46% on Santa Cruz. The threats which occur on this island also occur elsewhere throughout the species's range (e.g. anthropogenic habitat alteration and invasives) and so it may be inferred that the species is undergoing a rapid decline in the range of 30-49% over 3 generations.

Distribution and population

Certhidea olivacea is found in the Galápagos Islands, Ecuador, on the islands of Santa Cruz, Isabela, Fernandina, Santiago, Baltra, Pinzón and Rábida (del Hoyo and Collar 2016). It occurs in a range of habitat types, but the abundance of individuals recorded on Santa Cruz in 2008-2010 appear to be highest in Scalesia and fern dominated habitats, and lowest in dry and agricultural areas (Dvorak et al. 2012). This study also estimated the number of singing males at 55,500 (37,300-80,600) on Santa Cruz alone (Dvorak et al. 2012).

Ecology

The species occurs in a range of habitat types, but the abundance of individuals recorded on Santa Cruz in 2008-2010 appear to be highest in Scalesia and fern dominated habitats, and lowest in dry and agricultural areas (Dvorak et al. 2012).

Threats

The traditional strongholds for the species (upper transition and Scalesia zones) are the areas most threatened by anthropogenic habitat alteration (Dvorak et al. 2012). Scalesia has in particular been heavily impacted, with it having potentially covered most of Santa Cruz (Stewart 1915), but now only occurring in small scattered patches; and these have been invaded by non-native plants (Rentería and Buddenhagen 2006, Jäger et al. 2007, Dvorak et al. 2012). Control of these plants with herbicides, could also impact this species by impacting the plant community, and so affecting the the invertebrate community - the Warbler-finches' food source (Dvorak et al. 2012). Other invasive species may also be affecting Green Warbler-finch too, with rats, mosquitoes and the parasitic fly Philornis downsi all being potential threat to the avifauna of the Galápagos (Fessl and Tebbich 2002, Whiteman et al. 2005, Fessl et al. 2010, Dvorak et al. 2012).

Conservation actions

Conservation and Research Actions Underway
The species is found within the Galápagos National Park.

Conservation and Research Actions Proposed

Implement a full-scale monitoring programme for birds on the Galápagos islands in order to assess the impact of threats including diseases and habitat change and the effects of restoration (Dvorak et al. 2012). Continue research into Philornis downsi. Control introduced species. Protect remaining suitable habitat. Ensure management to control invasive plants does not impact negatively on the species.

Acknowledgements

Text account compilers
Westrip, J., Butchart, S., Symes, A., Ekstrom, J.


Recommended citation
BirdLife International (2022) Species factsheet: Certhidea olivacea. Downloaded from http://www.birdlife.org on 05/12/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 05/12/2022.