Techniques for monitoring Brachyramphus murrelets: A comparison of radar, autonomous acoustic recording and audio‐visual surveys

Abstract

Conditions in Alaska, USA, pose a challenge for monitoring populations of Brachyramphus murrelets using standard survey methods, because of strong winds, 2 sympatric species, short nights, and variable nesting habitat. We tested 3 methods for monitoring Brachyramphus murrelets breeding in the Kodiak Archipelago, Alaska, in 2010-2012. In addition to standard audio-visual and radar methods, we tested-for the first time with murrelets in Alaska-the application of autonomous acoustic recorders for monitoring vocal activity. We completed 74 radar, 124 audio-visual, and 134 autonomous acoustic surveys, focused on presunrise activity peaks; this yielded 26,375 murrelet detections. Marbled (B. marmoratus) and Kittlitz's murrelets (B. brevirostris) could not be distinguished using combinations of radar and acoustic recordings; therefore, at-sea surveys will be required to determine localized species proportions. Of the 3 methods, radar sampled the largest area and detected silently flying murrelets, providing the most reliable data on local populations; however, radar identification of murrelets was unreliable in winds exceeding 18 km/hr. Audio-visual surveys were useful for species identification and to document behaviors associated with local nesting, whereas autonomous acoustic recorders allowed season-long monitoring of murrelet vocal activity. Within potential forest-nesting habitat of marbled murrelets, all 3 methods gave similar measures of presunrise murrelet activity, but only radar reliably sampled murrelets commuting between nest and ocean. Because of their low cost and flexible programming, automated sound recorders offer an affordable way to sample vocal activity prior to more intensive or expensive radar and audio-visual surveys. We recommend that population monitoring and habitat studies of Brachyramphus murrelets in Alaska include combinations of all 3 methods. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Comparing imaging, acoustics, and radar to monitor Leach’s storm-petrel colonies

“…Acoustic call rates of surface nesting Forster’s terns ( Sterna forsteri ) yielded significant correlations with colony counts, however colony sizes were small, ranging from 15-111 breeding pairs (Borker et al, 2014). Finally, radar surveys have been used to measure changes in relative abundance of seabird populations for decades (Day et al, 2003; Cooper, Raphael & Peery, 2006; Raine et al, 2017), yet validation or comparative studies exist for a limited number of species (Bertram, Cowen & Burger, 1999; Cragg, Burger & Piatt, 2016).…”

Automated Recording Unit Detection Probabilities: Applications for Montane Nesting Seabirds1

“…The functional detection distance of the older Song Meter SM2 sensors was in line with the measured detection distance of these sensors for other species and habitats. In forested habitats, Marbled murrelets were detectable out to 60 m (Cragg et al 2015). Additionally, the effective detection distance of boreal songbirds was found to be 50 m (Venier et al 2012).…”

“…Passive acoustic studies of seabirds are increasingly using Song Meter acoustic sensors (Wildlife Acoustics Inc.) due to their affordability, compact size, and ease of use. Song Meter sensors have been used to determine the presence and distribution of Marbled murrelet (Brachyramphus marmoratus) and Ancient murrelet (Synthliboramphus antiquus) in Alaska, Newell's shearwater (Puffinus newelli) in Hawai'i, and Ashy storm-petrel (Oceanodroma homochroa) in California (Buxton and Jones 2012, Cragg et al 2015, Harvey et al 2016. Despite the widespread use of acoustic sensors to determine the presence and distribution of seabirds, only a single study has been conducted to determine the difference in detection probability in habitats of different physical structure and forest canopy openness (Cragg et al 2015).…”

Perspectives and challenges for the use of radar in biological conservation

“…Marine radar has also been used to monitor numbers and flight behaviour of threatened seabird species, such as petrels and shearwaters, terns, murrelets and other small auks as they move between breeding and feeding areas (Day and Cooper 1995, Cooper et al 2001, Raphael et al 2002, Day et al 2003, Hamer et al 2005, Cragg et al 2016, Urmy and Warren 2017, often during the night or at dawn and dusk. In murrelets, counts by marine radar cover much larger areas compared to audio-visual surveys or autonomous acoustic recording, but radar identification of murrelets proved unreliable in winds exceeding 18 km h -1 : strong tail winds increased flight speeds of all birds and head winds reduced them; in either case, differentiating murrelets from slower flying birds became problematic (Cragg et al 2016). Nonetheless, radar is capable of detecting population trends and providing information on habitat associations in areas where flight paths are confined by the landscape, such as fjords and valleys (Cragg et al 2016).…”

“…In murrelets, counts by marine radar cover much larger areas compared to audio-visual surveys or autonomous acoustic recording, but radar identification of murrelets proved unreliable in winds exceeding 18 km h -1 : strong tail winds increased flight speeds of all birds and head winds reduced them; in either case, differentiating murrelets from slower flying birds became problematic (Cragg et al 2016). Nonetheless, radar is capable of detecting population trends and providing information on habitat associations in areas where flight paths are confined by the landscape, such as fjords and valleys (Cragg et al 2016). Special-purpose entomological radar systems for observation and monitoring of insect migration (as opposed to foraging behaviour) were formerly mainly horizontal-scanning pencil-beam units, but since about the year 2000 these have been superseded by nutating vertical-beam systems which are much amenable to autonomous operation (Drake and Reynolds 2012, Drake 2016, Drake and Bruderer 2017, Drake and Wang 2018.…”