Contributed Paper Rates of Movement of Threatened Bird Species between IUCN Red List Categories and toward Extinction M. de L. BROOKE, ∗ ‡‡ S.H.M. BUTCHART,† S.T. GARNETT,‡ G.M. CROWLEY,‡§ N.B. MANTILLA-BENIERS, ∗ †† AND A.J. STATTERSFIELD† ∗ Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, United Kingdom †BirdLife International, Wellbrook Court, Girton Road, Cambridge CB3 0NA, United Kingdom ‡School for Environmental Research, Charles Darwin University, Darwin, NT 0909, Australia §Tropical Savannas Cooperative Research Centre, Charles Darwin University, Darwin, NT 0909, Australia ††Instituto Gulbenkian de Ciencia, Apartado 14, 2781-901 Oeiras, Portugal Abstract: In recent centuries bird species have been deteriorating in status and becoming extinct at a rate that may be 2–3 orders of magnitude higher than in prehuman times. We examined extinction rates of bird species designated critically endangered in 1994 and the rate at which species have moved through the IUCN (World Conservation Union) Red List categories of extinction risk globally for the period 1988–2004 and regionally in Australia from 1750 to 2000. For Australia we drew on historical accounts of the extent and condition of species habitats, spread of invasive species, and changes in sighting frequencies. These data sets permitted comparison of observed rates of movement through the IUCN Red List categories with novel predictions based on the IUCN Red List criterion E, which relates to explicit extinction probabilities determined, for example, by population viability analysis. The comparison also tested whether species listed on the basis of other criteria face a similar probability of moving to a higher threat category as those listed under criterion E. For the rate at which species moved from vulnerable to endangered, there was a good match between observations and predictions, both worldwide and in Australia. Nevertheless, species have become extinct at a rate that, although historically high, is 2 (Australia) to 10 (globally) times lower than predicted. Although the extinction probability associated with the critically endangered category may be too high, the shortfall in realized extinctions can also be attributed to the beneficial impact of conservation intervention. These efforts may have reduced the number of global extinctions from 19 to 3 and substantially slowed the extinction trajectory of 33 additional critically endangered species. Our results suggest that current conservation action benefits species on the brink of extinction, but is less targeted at or has less effect on moderately threatened species. Keywords: Australian birds, conservation impact, extinction rate, IUCN Red List criteria, threat category Tasas de Movimiento de Especies de Aves Amenazadas entre Categor´ ıas de la Lista Roja y hacia la Extinci´ on Resumen: En siglos recientes, el estatus de las especies de aves se ha deteriorado y se est´ an extinguiendo a una tasa que puede ser 2 a 3 ´ ordenes de magnitud mayor que en los tiempos prehumanos. Examinamos las tasas de extinci´ on de especies de aves designadas como cr´ ıticamente en peligro en 1994 y la tasa a la que las especies se han movido en las categor´ ıas de riesgo de extinci´ on de la IUCN globalmente entre 1988 y 2004 y regionalmente en Australia de 1750 a 2000. Para Australia, nos basamos en registros hist´ oricos de la extensi´ on y condici´ on del h´ abitat de las especies, en la dispersi´ on de especies invasoras y en cambios en las frecuencias de observaci´ on. Estos conjuntos de datos permitieron la comparaci´ on de las tasas observadas de movimiento en las categor´ ıas de amenaza de IUCN con predicciones nuevas basadas en el criterio E de la lista roja de IUCN, que se refiere a probabilidades expl´ ıcitas de extinci´ on determinadas, por ejemplo, por an´ alisis de viabilidad poblacional. La comparaci´ on tambi´en prob´ o si las especies enlistadas con base en otros criterios ‡‡email m.brooke@zoo.cam.ac.uk Paper submitted May 24, 2007; revised manuscript accepted September 26, 2007. 417 Conservation Biology, Volume 22, No. 2, 417–427 C 2008 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2008.00905.x