Using radar and sound recorders to study murrelets in Alaska - 2011
In 2011 our research in Alaska continued, focusing on the two species
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.
and Kittlitz's Murrelet Brachyramphus
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
. 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.
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
- Audio-visual: 58 hours; 674 murrelet detections;
- Song Meter: 903 hours; the number of detections is still being
Using the flight speed and flight path criteria we developed in the 2010 pilot study, we were able
to separate bird targets on the radar into:
- Likely Murrelets;
- Possible Murrelets;
- Other Birds
As part of Jenna's thesis work, these criteria will be refined and
contribute to a consistent murrelet monitoring protocol for Alaska.
Statistical analysis of the radar and AV data is underway.
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] &
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.