ORIGINAL ARTICLE Seasonal variation in stopover site use: Catharus thrushes and vireos in northern Colombia Camila Go ´mez • Nicholas J. Bayly • Kenneth V. Rosenberg Received: 25 August 2011 / Revised: 19 March 2012 / Accepted: 29 June 2012 Ó Dt. Ornithologen-Gesellschaft e.V. 2012 Abstract Migratory routes and stopover sites used by migrant landbirds may vary among seasons and years. Understanding the degree of such variation is an important aspect of migrant ecology, especially in South America, where routes and sites are not well known. We studied stopover site use by two Vireo species and three Catharus species in the Sierra Nevada de Santa Marta in northern Colombia during a two-year period. We used capture totals corrected for mist-net effort and density estimates derived from variable distance transect observations performed at sites located at three different altitudes and thus habitats to describe variation in stopover site use. Four of the five study species showed significant seasonal variation in terms of presence, such that ecologically similar species were present during opposite migration periods; for example, Vireo flavoviridis was an autumn migrant, while Vireo olivaceus was commonest in spring. A similar pat- tern was observed for Catharus fuscescens and Catharus minimus. We detected differences in density with habitat/ altitude, with C. minimus and Catharus ustulatus most abundant in pre-montane forest, while C. fuscescens abundance peaked in lowland forest. At the same altitude, Catharus species were more abundant in pre-montane forest than in shade coffee plantations. The abundance of C. ustulatus varied markedly between years during autumn migration, potentially in association with changes in the prevailing wind conditions. The temporal and spatial var- iation in stopover site use described here provides impor- tant insights into migratory strategies for Neotropical migrants within northern South America, and also regard- ing the multiple factors that may have shaped these strategies. Keywords Autumn migration Á Catharus Á Colombia Á Neotropical migrants Á Routes Á Sierra Nevada de Santa Marta Á South America Á Spring migration Á Strategy Á Vireo Zusammenfassung Jahreszeitliche Variation in der Nutzung von Rastge- bieten: Catharus-Drosseln und Vireos im no ¨rdlichen Kolumbien Vogelzugrouten und verfu ¨gbare Rastgebiete ko ¨nnen sai- sonal und auch zwischen den Jahren variieren. Ein besseres Versta ¨ndnis des Ausmaßes dieser Variation ist ein wichti- ger Aspekt der Vogelzugo ¨kologie, besonders in Su ¨dame- rika, wo Zugrouten und Rastgebiete oft nicht bekannt sind. Wir haben Rastgebiete von zwei Vireo- und drei Catharus- Arten in der Sierra Nevada de Santa Marta im no ¨rdlichen Kolumbien wa ¨hrend zwei Jahren untersucht. Zur Be- schreibung der Variation der Nutzung der Rastgebiete ver- wendeten wir die Gesamtzahl gefangener Vo ¨gel korrigiert um den Fangaufwand und Dichtescha ¨tzungen auf Grund- lage von verschiedenen Distanz-Transekt Za ¨hlungen in drei verschiedenen Ho ¨henlagen und verschieden Habitaten. Vier der fu ¨nf untersuchten Arten zeigten signifikante jahreszeitliche Variation in ihrer Anwesenheit. O ¨ kologisch a ¨hnliche Arten waren in den jeweils gegenla ¨ufigen Zugperioden anwesend. So war V. flavoviridis ein Communicated by C. G. Guglielmo. C. Go ´mez (&) Á N. J. Bayly SELVA: Investigacio ´n para la Conservacio ´n en el Neotro ´pico, Calle 41 No 26B, 58, Apto 401, Bogota ´, Colombia e-mail: camila.gomez@selva.org.co K. V. Rosenberg Cornell Lab of Ornithology, 159 Sapsucker Wood Road, Ithaca, NY 14850, USA 123 J Ornithol DOI 10.1007/s10336-012-0876-5