LAUSR

Markham's Storm-Petrel Oceanodroma markhami is one of the least known seabirds in the world. Between 2013 and 2017, we conducted an extensive ground based survey to locate nests, confirm nesting colonies and, whenever possible, characterize Markham's Storm-Petrel breeding phenology. The survey was conducted in the Atacama Desert, northern Chile, covering the area between Arica (18.240°S, 70.509°W) and Taltal (25.050°S, 70.486°W). Our study led to the discovery of two new colonies and to a six-fold increase in the estimate of the breeding population at the previously known Arica colony: a more accurate estimate of 55,308 pairs. Prior to this study, 9362 breeding pairs were known to occur in two colonies. Currently, the colonies of Arica (34,684 nests), Pampa La Perdiz (624 nests) and Salar Grande (20,000 nests) represent almost 95% of the known breeding population. We found that the colony of Arica has a different breeding phenology to that of the Pampa Perdiz and Salar Grande colonies, which could be due to differences in their food phenology. None of the colonies lie within designated protected areas and they strongly overlap with current and planned mining, wind farms and power plants in northern Chile. Apart from the disturbance caused by destruction of habitat and nests, these developments are also important sources of artificial light that cause the grounding of fledglings, after which many of them probably die from the collision impact or predation. It is vital to ensure the conservation of this species by protecting their breeding grounds and by reducing the light pollution not only in the colonies, but also at the access points to the colonies and at the big cities nearby.