Poster-Oppel-Et-Al.Pdf

Oppel, S. et al. 2014. BOU Proceedings – Avian Demography in a Changing World http://www.bou.org.uk/bouproc-net/avian-demography/poster-oppel-et-al.pdf

Proceedings of the BOU’s 2013 Annual Conference From populations to policy impact: avian demography in a changing world

View other papers from these proceedings at www.BOUPROC.net.

POSTER

Assessing population viability of a tropical forest songbird using an integrated population model

STEFFEN OPPEL1*, GEOFF HILTON1, NORMAN RATCLIFFE3, RICHARD ALLCORN3, CALVIN FENTON3, JAMES DALEY3, JULIET VICKERY1 & DAVID GIBBONS1 1 Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG 19 1QX, UK 2 British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK 3 Montserrat Department of the Environment, PO Box 272, Brades, Montserrat, West Indies

* Email: [email protected]

The viability of bird populations can be influenced by climatic conditions and by the occurrence of rare events. For many animal populations several demographic processes can respond to environmental perturbations, and understanding the population-level effects of environmental variation requires information on several important demographic variables, such as adult and juvenile survival probabilities, and annual fecundity. For rare species it can often be challenging to obtain sufficient data to estimate all the demographic parameters required for assessing the viability of a population.

Integrated population models facilitate the integration of census data and all existing demographic information from a species to estimate demographic parameters for which no empirical data exist (Besbeas et al. 2004, 2005, Schaub et al. 2007, 2010). Because integrated population models incorporate uncertainty around all demographic parameters, they are an ideal tool for population viability analyses (Kéry & Schaub 2012). We used an integrated population model to assess the past and future population trend of a tropical forest passerine, the Montserrat Oriole Icterus oberi. Montserrat Orioles are endemic to the Caribbean island of Montserrat, where an ongoing volcanic eruption has recently destroyed much of the native forest habitat. The Montserrat Oriole is currently considered as ‘Critically Endangered’, and suffers from ongoing volcanic activity and introduced predators affecting nest survival (Hilton et al. 2003, Allcorn et al. 2012, Oppel et al. 2013). We used population monitoring data (2000– 2012), productivity data (2001–2005) and mark–recapture data of juvenile and adult birds (2000–2005) in an integrated population model to estimate unobservable demographic parameters such as true juvenile survival and immigration rate. We considered volcanic ash-fall effects on annual survival probabilities, and effects of pre-breeding season rainfall on annual fecundity to explain annual fluctuations in Montserrat Oriole abundance. We projected the population trend 8 years into the future to assess the immediate extinction probability of Montserrat Orioles under current rainfall and volcanic activity.

Montserrat Orioles experienced lower survival in years with volcanic ash-fall, and this effect caused periodic population declines that were compensated for by higher seasonal fecundity in years with high pre-breeding season rainfall. The integrated population model estimated a mean population growth rate

Oppel, S. et al. 2014. BOU Proceedings – Avian Demography in a Changing World http://www.bou.org.uk/bouproc-net/avian-demography/poster-oppel-et-al.pdf

Proceedings of the BOU’s 2013 Annual Conference From populations to policy impact: avian demography in a changing world

View other papers from these proceedings at www.BOUPROC.net. of 0.983 (95% credible interval 0.958–1.007) between 2000 and 2012, and was able to trace the observed population fluctuations during that period. True annual juvenile survival probability in non- volcano years (0.517; 0.350–0.735) was 66% of adult survival (0.752; 0.668–0.830). Juvenile dispersal from the study area, which heavily influenced apparent juvenile survival probabilities estimated from mark–resighting data, was compensated for by an immigration component in our model, which indicated a local immigration rate of 16.1% (5.9– 26.9%) of the population per year.

Due to the inclusion of both demographic and environmental uncertainty in the model, the estimated population growth rate in the immediate future was highly imprecise (95% credible interval 0.844– 1.132). Although the Montserrat Oriole is vulnerable to ongoing volcanic activity, the population can compensate for periodic population setbacks under current climatic conditions, and these environmental uncertainties need to be considered in management options formulated for this species. Our model provides reassurance that the Montserrat Oriole is currently not threatened with immediate extinction in the near future, but that annually varying environmental conditions can explain considerable annual fluctuations in the species’ abundance. Based on the very low probability of extinction in the near future, emergency conservation interventions for the Montserrat Oriole are probably unnecessary, but the protection of all remaining forest habitat will be critical to maintain a viable Montserrat Oriole population.

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