Using radar and sound recorders to study murrelets in Alaska - 2011
In 2011 our research in Alaska continued, focusing on the two species
of Brachyramphus
murrelet which breed there. Based on our 2010 pilot study we continued
radar research on Kodiak Island and tested out recently developed
technology for automated recording of bird songs (Song Meters). Our
2011 research was funded by the North Pacific Research Board
with essential equipment and
logistical support from Dr.
John Piatt, US Geological Survey, Alaska Science Center and the Kodiak National Wildlife Refuge. See our Marbled Murrelet radar page for more details about the use of radar in tracking murrelets and our Radar Studies in Alaska 2010 page for information on the pilot study at Grant Lagoon, Kodiak Island.
Marbled Murrelet Brachyramphus marmoratus (left) and Kittlitz's Murrelet Brachyramphus brevirostris (right).
Radar, AV and automated sound surveys
UVic graduate student Jenna Cragg and her assistant Stacey Hrushowy set out to do a series of simultaneous radar counts, automated sound recordings and audio-visual surveys. The radar involved a standard marine X-band radar modified to pick up flying birds (scanning antenna is tilted slightly upward; rain and sea clutter supressors turned off; gain adjusted for high sensitivity). The radar was mounted on a truck, for sites with road access, and on the Kodiak National Wildlife Refuge's vessel Ursa Major II for sites along the southern coast of Kodiak Island. Audio-visual (AV) surveys involve a human observer located near the radar station to record all the birds seen and heard during the radar counts, following the standard Pacific Seabird Group Marbled Murrelet survey protocol. Generally, the AV observer detects only a fraction of the flying birds detected by the radar - this is because murrelets commute in dark evening and morning twilight, making them hard to see, and the radar also scans a much larger area than the human observer can.
High-frequency radar used to track flying birds on Kodiak Island, mounted on a truck (left) and the vessel Ursa Major (right)
Automated recordings of vocalizations and wing-beats were made with the Song Meter made by Wildlife Acoustics. These devices are designed to record bird song automatially in digital format. Using sound recognition software researchers can then get measures of the different species and the frequencies of their calls. Although radar has been used numerous times to track Marbled Murrelets, our study appears to be the first to combine radar with automated sound recording to help identify the birds being tracked on the radar. The Song Meters were mounted in trees and oriented to pick up calls of murrelets flying overhead.
A Wildlife Acoustics Song Meter mounted on a tree (left) and Stacey setting up a Song Meter in the forest on Kodiak Island.
Jenna and Stacey were able to deploy an array of Song Meters in likely forest nesting habitat for Marbled Murrelets, and along flight paths leading to other nesting areas inland. In this example shown here, at the radar station at Monashka Bay, six Song Meters (red dots) were deployed within the scanning radius of the radar (the red circle).
Through the 2011 summer season a huge
quantity of data were collected at 16 sites on Kodiak Island:- Radar: 160 hours; over 7,000 detections of potential murrelet targets;
- Audio-visual: 58 hours; 674 murrelet detections;
- Song Meter: 903 hours; the number of detections is still being analysed.
- Likely Murrelets;
- Possible Murrelets;
- Other Birds
Analyis of the Song Meter data involves developing sound recognition algorithms to specifically identify each species from the digital recordings of their calls. Here is an example of a spectrogram of a series of Marbled Murrelet calls showing the amplitude of sound at various sound frequencies.
Time runs along the x-axis and sound frequency on the y-axis.Click on the spectrogram to hear a series of Marbled Murrelet "keer"calls.
[You might need to click on the "go back one page" arrow afterwards to return to this page.]
Once the sound recognition algorithms have been developed for Marbled Murrelet and Kittlitz's Murrelet, the 900+ hours of recordings can be analysed to determine the number of calls and the diurnal, seasonal and spatial patterns of the sounds. The sound records of murrelets will then be compared with the counts and activity patterns recorded in the radar and AV surveys. We will post more information here once these results become available.
Vessel Surveys off Kodiak Island
In 2011 Jenna Cragg assisted with the at-sea surveys undertaken each year by Robin Corcoran of the Kodiak National Wildlife Refuge. Using the refuge's vessel Ursa Major II, Robin's study sytematically covers a series of linear transects along the nearshore Kodiak Island coast. Murrelets and other seabirds are counted using standard methods and these data are important for long-term monitoring of local populations of both Marbled and Kittlitz's murrelets. The at-sea surveys were conducted as part of the Southwest Alaska Network (SWAN) coastal monitoring program. One of the goals of the SWAN surveys is to estimate breeding productivity for both murrelet species, and special care is given to identifying newly-fledged (hatching year) murrelets of both species in August. Productivity is usually measured as the ratio of hatching-year to after-hatching-year (adults and immatures in adult plumage) birds.
The Ursa Major II in a bay off Kodiak Island, at-sea survey observer, and a pair of adult Marbled Murrelets (photos © Jenna Cragg, David Sinnett [USDA] & Alan Burger)
By participating in these surveys Jenna was able to do radar surveys at several coastal locations on Kodiak island which can only be reached by boat. She also plans to use some of the count data to compare radar counts of murrelets flying inland with at-sea counts of murrelets on the water in their marine foraging areas. Such comparisons have not been done in any previous study and Jenna and Robin's data should contribute to better understanding of the interactions between marine foraging and inland nesting habitats of both murrelet species. Data from 86 transects involving counts of over 2,300 murrelets (mainly Marbled Murrelets) are currently being analysed.
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