In the Salish Sea, there has been a shift in the nesting behavior of cormorants from cliffs and offshore islets (Chatwin et al. 2003) to man-made structures like bridges and hydro-electric towers (Butler 2015). These man-made structures are found within the greater city of Vancouver, a large urban centre of 2.5 million people. This proximity to the city may expose cormorants to anthropogenic stresses like commercial vessel transits, ferries (Aquabus), speedboats, and other small recreational boats (e.g., kayaks, dragonboats), and higher ambient noise levels from vehicle and train traffic as well as noise from Vancouver’s industrial port activities. On the other hand, these man-made structures may make breeding birds immune from terrestrial predators and less vulnerable to aerial predation by bald eagles (Haliaeetus leucocephalus) and gulls and therefore less prone to nest abandonment (Hipfner et al. 2012).
Breeding pairs of cormorants are difficult to census due to their remotely located and vertically‑oriented colonies. Conventional monitoring surveys of cormorants have been conducted using in-person observation using boat-based methods and binoculars. Studies on Triangle Island have been conducted in-person by using a viewing blind situated above the nests and cormorant colonies so that the adult cormorants were surveyed when they stood up (Hipfner and Greenwood 2009). However up to 2015, little was known about the timing and success of pelagic cormorant breeding colony sites along BC coasts (Hipfner and Greenwood 2009), including those of urban structures (Hipfner 2015, Butler 2015). The traditional census method for urban bridge occupancy involves looking up at near right-angles from a moving boat making it difficult to observe all nesting birds. Nonetheless, census numbers at Vancouver’s Second Narrows Bridge (i.e. Vancouver’s Ironworkers Memorial Bridge) estimated a minimum of 200 nesting pairs of pelagic cormorants (Hipfner 2015) and 93 nesting pairs of double-crested cormorants (Butler 2015). Although nesting numbers beneath Granville Street Bridge are unknown, it is well understood that this bridge is an important breeding site for cormorants (Butler 2015).
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