Contributed Paper Analyzing Variability and the Rate of Decline of Migratory Shorebirds in Moreton Bay, Australia HOWARD B. WILSON, ∗ † BRUCE E. KENDALL,†† RICHARD A. FULLER, ∗ ‡ DAVID A. MILTON,§ AND HUGH P. POSSINGHAM ∗ ∗ The University of Queensland, Ecology Centre, St Lucia, Queensland 4072, Australia ††Bren School of Environmental Science & Management, University of California, Santa Barbara, Santa Barbara, CA 93106-5131, U.S.A. ‡CSIRO Climate Adaptation Flagship and CSIRO Sustainable Ecosystems, St Lucia, Queensland 4072, Australia §Queensland Wader Study Group, 336 Prout Road, Burbank, Queensland 4156, Australia Abstract: Estimating the abundance of migratory species is difficult because sources of variability differ substantially among species and populations. Recently developed state-space models address this variability issue by directly modeling both environmental and measurement error, although their efficacy in detecting declines is relatively untested for empirical data. We applied state-space modeling, generalized least squares (with autoregression error structure), and standard linear regression to data on abundance of wetland birds (shorebirds and terns) at Moreton Bay in southeast Queensland, Australia. There are internationally significant numbers of 8 species of waterbirds in the bay, and it is a major terminus of the large East Asian- Australasian Flyway. In our analyses, we considered 22 migrant and 8 resident species. State-space models identified abundances of 7 species of migrants as significantly declining and abundance of one species as significantly increasing. Declines in migrant abundance over 15 years were 43–79%. Generalized least squares with an autoregressive error structure showed abundance changes in 11 species, and standard linear regression showed abundance changes in 15 species. The higher power of the regression models meant they detected more declines, but they also were associated with a higher rate of false detections. If the declines in Moreton Bay are consistent with trends from other sites across the flyway as a whole, then a large number of species are in significant decline. Keywords: migratory species, population declines, shorebirds, state-space models, variability An´ alisis de la Variabilidad y Tasa de Declinaci´ on de Aves Vadeadoras Migratorias en la Bah´ ıa Moreton, Australia Resumen: La estimaci´ on de la abundancia de especies migratorias es dificil porque las fuentes de variabil- idad difieren sustancialmente entre especies y poblaciones. Modelos de estado-espacio desarrollados reciente- mente abordan el tema de la variabilidad mediante la modelaci´ on directa de los errores ambientales y de medici´ on, aunque su eficacia para la detecci´ on de declinaciones no ha sido probada con datos emp´ ıricos. Aplicamos modelos estado-espacio, m´ ınimos cuadrados generalizados (con estructura de autorregresi´ on de error), y regresi´ on lineal est´ andar a datos sobre abundancia de aves de humedales (aves vadeadoras y golondrinas de mar) en la Bah´ ıa Moreton en el sureste de Queensland, Australia. En la bah´ ıa hay n´ umeros significativos internacionalmente de 8 especies de aves acu´ aticas, y es un importante punto final del Corredor Asia-Australasia Oriental. En nuestros an´ alisis, consideramos 22 especies migratorias y 8 residentes. Los mod- elos estado-espacio identificaron que las abundancias de 7 especies migratorias declinaron significativamente y que la abundancia de una especie aument´ o significativamente. Las declinaciones en la abundancia de es- pecies migratorias a lo largo de 15 a˜ nos comprendieron entre 43 y 79%. Los m´ ınimos cuadrados generalizados con estructura de autorregresi´ on de error mostraron cambios en la abundancia de 11 especies, y la regresi´ on lineal est´ andar indic´ o la declinaci´ on en 15 especies. El mayor poder de los modelos de regresi´ on significa que †email h.wilson1@uq.edu.au Paper submitted August 9, 2010; revised manuscript accepted December 8, 2010. 1 Conservation Biology, Volume **, No. **, ***–*** C 2011 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2011.01670.x