Population decline and demography of the world’s largest breeding population of huemul deer (Hippocamelus bisulcus) in Bernardo O'Higgins National Park, Chile

Abstract

The largest remaining populations of the endangered huemul deer (Hippocamelus bisulcus) are believed to be concentrated in the remote, rugged and largely uninhabited glacial valleys and fjords surrounding the Southern Patagonian Ice Field that lie within Chile's Bernardo O'Higgins National Park. On the Park's northwestern edge is Bernardo Fjord, an area home to the world's largest known breeding population of huemul. We present a demographic study of this population and examine its population trends since 2004. We conducted huemul transect surveys on-foot during 16 expeditions to Bernardo Fjord from October 2014 to March 2020, during which we spent a total of 254 days in the field and documented 284 observations of huemul. This coastal population of huemul exhibited higher female proportions (mean 0.64 AE SD 0.05), lower fawn:female ratios (mean 0.18 AE SD 0.23 in March and mean 0.22 AE SD 0.07 in November), and similar group sizes (mean 1.77 AE 1.06 SD individuals) to previous studies. Huemul densities in Bernardo Valley encountered from 2016 to 2019 were 60% lower than densities observed in a previous study from 2004 to 2008. We produce a 2019 huemul population estimate for Bernardo Fjord of 84 (AESD 7) individuals including 44 observed individuals and 40 (AESD 10) individuals estimated to be undetected by our surveys, which comprises 6-8% of the IUCN global population estimate. Two of the surveyed sectors -Bernardo Valley and Pampaare of critical conservation importance, given that the 5 km 2 Pampa is home to 42% of the total huemul population and 41% of the fawn population of Bernardo Fjord. We examine potential drivers of this population decline, which may include poor recruitment, predation and high incidences of foot disease exacerbated by climatic conditions, and we offer recommendations for the conservation, monitoring and management of this and other coastal huemul populations.Las mayores poblaciones remanentes del amenazado Huemul (Hippocamelus bisulcus) se cree que est an concentradas en los remotos, accidentados y mayoritariamente inahabitados valles glaciares y fiordos que rodean el Campo de Hielo Patag onico Sur, la mayor parte del cual est a contenido en el Parque Nacional Bernardo O'Higgins en Chile. En el borde noroeste est a el Fiordo Bernardo, un area que alberga la poblaci on reproductiva m as grande conocida. Presentamos un estudio demogr afico de esta poblaci on y analizamos su tendencia poblacional desde 2004. Recorrimos a pie transectos de huemul durante 16 expediciones en el Fiordo Bernardo, desde Octubre de 2014 hasta Marzo de 2020, durante las cuales permanecimos un total de 254 d ıas en terreno y registramos 284 observaciones de huemules. Esta poblaci on costera de huemul mostr o una proporci on mayor de hembras (media 0.64 AE SD 0.05), una relaci on cr ıa:hembra menor (media 0.18 AE SD 0.23 en Marzo y media 0.22 AE SD 0.07 en Noviembre), y tamaños de grupo similares (media 1.77 AE SD 1.06 individuos), que en estudios previos. Las densidades de huemules que se encontraron para el Fior...