Population trends of Imperial Cormorants (Leucocarbo atriceps) in northern coastal Argentine Patagonia over 26 years

Abstract

Monitoring programmes are essential for detecting population changes, but data series are difficult to sustain over time. Additionally, wide-scale monitoring is needed to adequately interpret demographic behaviour given the metapopulation dynamics characteristics ofmost seabird species and to understand the underlying factors, such as anthropogenic pressures and climate change. Many cormorant species are largely dependent on coastal marine environments, which are subject to increasing pressures from human activities. Here, we update information on the distribution and size of Imperial Cormorant (Leucocarbo atriceps) colonies along 1,000 km of coastline in Argentina, and review published information to assess population trends at different spatial scales over 26 years (1990-2016). During 2016, the number of nests per colony ranged between 2 and 5,617 (median: 441 nests; n = 26). Total number of breeding pairs was estimated at 21,482. During the study period, two new locations were colonised, whilst another two were abandoned. Significant growth rates ranged from 1.022 to 1.117 (median: 1.036; n = 6) for increasing colonies and from 0.580 to 0.977 (median: 0.962; n = 8) for declining colonies, but the overall breeding population remained stable between 1990 and 2016 (λ = 1.000, C.I. 95% = 0.991-1.008). Our study provides one of the longest time series on seabird breeding numbers along a wide coastal sector in South America. Given the high yearly variability in nest numbers at individual Imperial Cormorant colonies, as well as the observed establishment and extinction of colonies, large scale and long term monitoring is necessary for a comprehensive understanding of overall changes in the population distribution patterns.