Bird Conservation International (2015) 25 :479 –488 . © BirdLife International, 2014 doi:10.1017/S0959270914000367 Multi-scale habitat use analysis and interspecific Ecology of the Critically Endangered Black-breasted Puffleg Eriocnemis nigrivestis ESTEBAN A. GUEVARA , ELISA BONACCORSO and JOOST F. DUIVENVOORDEN Summary The Black-breasted Puffleg Eriocnemis nigrivestis is a hummingbird endemic to Ecuador and consid- ered Critically Endangered, given its limited distribution, low population numbers, and ongoing habi- tat degradation. We investigated habitat use patterns using landscape and microhabitat variables. In addition, we explored a previously postulated competition hypothesis involving the Black-breasted Puffleg and the Gorgeted Sunangel Heliangelus strophianus . Our results suggest that landscape vari- ables may play a role in the habitat selection process; specifically the distance to nearest forest border seems to have a significant effect on our habitat model. We speculate that, as the species is known to perform seasonal movements, the avoidance of forest border might reduce the physiological stress caused by altitudinal migration. At microhabitat level, Black-breasted Puffleg seems not sensitive to forest structure variables. Our findings suggest that ensuring forest tract connectivity, between the altitudinal extremes of the species’ range at the north-western flanks of the Pichincha volcano, might be crucial for survival of the species during its annual cycle. However, non-metric multidimensional scaling (NMDS) indicates that Black-breasted Puffleg and the Gorgeted Sunangel do not overlap spatially, but this finding is not conclusive considering our field observations. Resumen Eriocnemis nigrivestis es un colibrí endémico de Ecuador, considerado Críticamente Amenazado debido a su distribución restringida, reducido tamaño poblacional y pérdida continua de su hábitat. Investigamos los patrones de uso de hábitat por parte de la especie, empleando variables a nivel de paisaje y micro hábitat. Adicionalmente exploramos la hipótesis de competencia entre Eriocnemis nigrivestis y Heliangelus strophianus que ha sido previamente postulada. Nuestros resultados sugieren que las variables de paisaje como la distancia al borde de bosque más cercano tendrían un rol en el proceso de selección de hábitat. Especulamos que la especie, en términos generales, evite los bordes de bosque con el fin de reducir el ya existente estrés fisiológico que la migración altitudinal conlleva. A nivel de microhábitat, Eriocnemis nigrivestis aparentemente no responde a las variables relacionadas con la estructura del bosque. Nuestros resultados también sugieren que para incremen- tar las probabilidades de sobrevivencia de la especie es necesario asegurar la conectividad entre frag- mentos de bosque ubicados a lo largo del rango altitudinal de la especie en los flancos nor-occidentales del volcán Pichincha. Por otro lado, a pesar de que nuestros hallazgos indican que Eriocnemis nigrivestis y Heliangelus strophianus no se solapan espacialmente, pensamos que estos resultados no son concluyentes considerando nuestras observaciones de campo. Introduction Hummingbird species of the Eriocnemis genus inhabit a wide range of habitats including forest, borders, and sub-paramo in the subtropical and temperate zones of the Andes, ranging at altitudes E. A. Guevara et al. 480 of ∼ 1000–5000 m (Schuchmann et al. 2001 , Cortes-Diago et al. 2007 ). One of those species is the Black-breasted Puffleg Eriocnemis nigrivestis , which is endemic to Ecuador and regarded as ‘Critically Endangered’ (BirdLife International 2012 ). Two arguments support this conservation status. The first is its limited global distribution (∼ 68 km 2 ) which is divided into two confirmed subpopula- tions, one on the north-western flanks of Pichincha volcano, in Pichincha province, and the other located in the Toisan mountain range in Imbabura province (BirdLife International 2012 ). Jahn ( 2008 ) reported historical specimens collected at Atacazo volcano, in Pichincha province; however, there are no recent surveys confirming the persistence of this population. The second argument is its small population size, recently estimated in the range of 250–999 individuals (Jahn 2008 ). Little information on the ecological requirements (e.g. nest and foraging site selection) of the Black-breasted Puffleg has been published to date (but see Jahn 2008 ), probably because of its scarcity and elusive habits. Bleiweiss and Olalla ( 1983 ) have referred to ridge-crest elfin forest as Black-breasted Puffleg habitat. However, recent information indicates that the species may also be found in shrubby forest borders, steep slopes with stunted vegetation, and the interior of mature montane forest (Jahn and Santander 2008 ). In any case, the species’ presence seems not to be determined by the occurrence of a particular feeding plant since it has been recorded feeding at a wide range of ornitophilous plant species (Bleiweiss and Olalla 1983 , Jahn and Santander 2008 ). Habitat use is considered the result of the habitat selection process in which individuals choose the habitat that provides environmental conditions appropriate for survival, reproduction, and population persistence (Boyce and McDonald 1999 ). Research on habitat use by terrestrial threat- ened bird species has shown that fine-scale features of forest physiognomy might be relevant in discriminating patterns in habitat usage (Bonaccorso and Barreto 2002 , Oppel et al. 2004 , Cahill and Matthysen 2007 ). Nevertheless, habitat selection may be seen as a spatially hierarchical process (Johnson 1980 ), in which species choose suitable conditions first at a broader scale (e.g. landscape) and then at a more narrow scale (microhabitat). Therefore, a complete habitat assessment may include multiple scales of research (McClure et al. 2012 ). Along the distributional range of the Black-breasted Puffleg, formerly pristine habitat has been heavily disturbed, especially because of the expansion of the agricultural frontier and human-induced burning of grassland and forest habitats (Jahn and Santander 2008 ). This situation has given rise to a matrix of different landscapes including forest patches, cattle pastures, and forest borders, making habitat assessments at different spatial scales essential for planning conservation efforts. The way in which species that exploit similar resources coexist in space and time is a central mat- ter in community ecology (Martin 2001 , Sheth et al. 2009 ). Several mechanisms such as habitat selection, spatial distribution, and morphological differentiation have been proposed to explain the coexistence of organisms and the maintenance of community assemblages (Stevens and Willig 2000 , Martin 2001 ). Recently, concern has been raised over the apparent altitudinal range extension of the Gorgeted Sunangel Heliangelus strophianus , a species that could be a potential competitor to the Black-breasted Puffleg (Jahn 2008 , Jahn and Santander 2008 ). Determining whether the more widely distributed Gorgeted Sunangel is a better competitor might contribute to an understanding of recent declines in the abundance of the ‘Critically Endangered’ Black-breasted Puffleg. In this study we aim to test hypotheses on whether the Black-breasted Puffleg responds to microhabitat and landscape variables, measured as vegetation structure and distance to nearest forest border respectively. In addition we explore potential competition among Black-breasted Puffleg and other hummingbird species in hummingbird communities. Methods Study area The study area is located on the north-western flanks of the Pichincha volcano, Pichincha province, north-western Ecuador, covering an altitudinal range of 2,700–3,500 m ( Figure 1 ); it lies within the Mindo Important Bird Area (IBA; Freile and Santander 2005 ) and two natural formations are Black-breasted Puffleg ecology 481 Figure 1. Location map of the four study sites on the north-western flanks of the Pichincha volcano, Pichincha province, Ecuador. Elevation ranges in m are represented by grey gradient colours, from darkest grey to lightest: > 3,400, 3,000–3,400, 2,400–3,000, 2,000–2,400 and < 2000. Thin black lines = rivers; thick black lines = study transects; black triangles = record sites at Esperanza Hill and black circles = towns. identified: montane cloud forest and evergreen high-mountain forest (Sierra 1999 ). We estab- lished three 1.2-km transects at three different sites within our study area: 1) Yanacocha reserve 2) Verdecocha reserve and 3) Alaspungo community reserve. All transects were at a minimum distance of 500 m from each other. Our study sites further included the Esperanza hill, where the Black-breasted Puffleg has also been recorded during observations performed outside the study transects. Details of coordinates and the elevation of each transect and Esperanza hill are provided in Table1. Appendix S1 in the online supplementary material summarises all Black-breasted Puffleg and Gorgeted Sunangel records at these sites. Bird surveys Bird censuses were performed applying the “multi-time window transect-mapping” (MTW) protocol for audio-visual monitoring studies (Jahn 2011 ). A complete survey session accord- ing MTW methodology consisted of 24 samples at each transect, accomplished within a mini- mum of six days (four samples per day). A sample, according to the MTW protocol, consists of an observation walk along the entire transect route in one direction (Jahn 2011 ). The dura- tion