J. Field Ornithol. 84(1):32–39, 2013 DOI: 10.1111/jofo.12003 Determining productivity of Maui Parrotbills, an endangered Hawaiian honeycreeper Hanna L. Mounce, 1,2,6 David L. Leonard, 3 Kirsty J. Swinnerton, 4 C. Dustin Becker, 5 Laura K. Berthold, 1 Kelly J. Iknayan, 1 and Jim J. Groombridge 2 1 Maui Forest Bird Recovery Project, Makawao, Hawaii 96768, USA 2 Durrell Institute of Conservation and Ecology, School of Anthropology and Conservation, University of Kent, Canterbury, Kent CT2 7NR, United Kingdom 3 Pacific Cooperative Studies Unit, Division of Forestry and Wildlife, Honolulu, Hawaii 96813, USA 4 Island Conservation, Santa Cruz, California 95060, USA 5 Life Net Nature, Wilcox, Arizona 85643, USA Received 18 August 2011; accepted 8 October 2012 ABSTRACT. Maui Parrotbills (Pseudonestor xanthophrys), critically endangered Hawaiian honeycreepers endemic to the island of Maui, are restricted to a single population of ∼500 individuals located in remote, mountainous terrain. From January to June 2006–2011, we located nests and fledglings in the Hanawi Natural Area Reserve (NAR) in east Maui, Hawaii, to document nest success and annual reproductive success. Nest success is a commonly used measure of productivity and is a central component of many demographic studies. Annual reproductive success is less frequently documented because greater effort is required to monitor the reproductive success of breeding pairs through time. However, for species whose nests are difficult to locate or access, such as Maui Parrotbills, the presence or absence of fledged young may provide a more accurate measure of breeding success than monitoring nests. During our study, we located and determined the outcome of 30 nests to document nest success, and monitored 106 territories for the presence or absence of fledglings to calculate annual reproductive success. Nest success probability was 19% (N = 30) and seasonal nest success was 46%. During our monitoring efforts, 49 of 106 breeding pairs produced a single fledged young. Because parrotbills typically have single egg clutches and only re-nest after nests fail, the presence or absence of a fledgling is an indication of a pair’s overall reproductive success for a breeding season. Based on the number of fledglings per pair, our estimate of annual reproductive success was 46%, confirming our initial productivity estimate from nests. Thus, our results indicate that the two methods, determining annual reproductive success by monitoring fledglings and calculating nest success, provide similar estimates of annual productivity for Maui Parrotbills. Based on our estimates, the parrotbill population appears to be demographically stable. However, our productivity estimate was based only on the population at Hanawi, an area representing just 3% of the total range of parrotbills. Thus, our results may not accurately reflect the status of parrotbills over their entire range. RESUMEN. La determinaci ´ on de la productividad de Pseudonestor xanthophrys, un ave Hawaiana en peligro de extinci ´ on La especie Pseudonestor xanthophrys es un ave en peligro cr´ ıtico y end´ emico a la isla de Maui, y se limita a una sola poblaci´ on de ∼500 individuos, ubicados en lugares remotos y monta˜ nosos. De enero a junio 2006–2011, localizamos nidos y volantones en el Hanawi Natural Area Reserve (NAR) en el este de Maui, Hawaii, para documentar el ´ exito de nidificaci´ on y el ´ exito reproductivo anual. El ´ exito de los nidos es una medida de productividad com´ unmente utilizada y es un componente central de muchos estudios demogr´ aficos. El ´ exito reproductivo anual es menos documentado porque requiere de un mayor esfuerzo para monitorear el ´ exito reproductivo de las parejas a trav´ es del tiempo. Sin embargo, para las especies cuyos nidos son dif´ ıciles de localizar o acceder, como P. xanthophrys, la presencia o ausencia de volantones puede proporcionar una medida m´ as precisa del ´ exito reproductivo que el monitoreo de nidos. Durante nuestro estudio, localizamos y determinamos el resultado de 30 nidos para documentar el ´ exito de los nidos, y monitoreamos 106 territorios para determinar la presencia o ausencia de volantones, para calcular el ´ exito reproductivo anual. La probabilidad del ´ exito de nidos fue de 19% (N = 30) y el ´ exito de nidificaci´ on por temporada fue de 46%. Durante nuestros esfuerzos de monitoreo, 49 de 106 parejas produjeron un solo volant´ on. Por la raz´ on que P. xanthophrys suele tener un solo huevo por puesta, y s´ olo re-nidifican despu´ es de que el nido falla, la presencia o ausencia de un volant´ on indica el total ´ exito reproductivo de una pareja para una temporada de cr´ ıa. Basado en el n´ umero de volantones por pareja, nuestra estimaci´ on del ´ exito reproductivo anual fue de 46%, lo que confirma nuestra estimaci´ on inicial de productividad, usando el ´ exito de los nidos. Por lo tanto, nuestros resultados indican que los dos m´ etodos (la determinaci´ on del ´ exito reproductivo anual mediante 6 Corresponding author. Email: mounce@hawaii.edu C  2013 The Authors. Journal of Field Ornithology C  2013 Association of Field Ornithologists 32 Journal฀of฀Field฀Ornithology