And I'd like to add that the research was done out of the University of Minnesota, as part of the GWWA study that was presented at the recent paper session, and the Univ. Of Tennessee, though the lead author has moved onto UCB.
Paul Paul Budde [email protected] <div>-------- Original message --------</div><div>From: Refsnider <[email protected]> </div><div>Date:12/22/2014 5:18 PM (GMT-05:00) </div><div>To: [email protected] </div><div>Subject: [mou-net] Golden-winged Warbler Clarification </div><div> </div>I want to clarify an earlier post today regarding Golden-winged Warblers (GWWA) which contained a link to a brief, but very interesting, BBC piece on temporarynesting areaabandonment to avoid tornadic activity. Gordon Andersson mentioned "an apparent 50% mortality [unrelated to the tornadoes] of the 20 study birds [carrying geolocators] in one year." This is not quite correct. The researchers resighted 10 of the 20 geolocator-bearing study birds a year after the attachment of geolocators and color bands. One bird already had dropped the geolocator somewhere, so if he is excluded from analysis, 9 of the 19 geolocator birds--47%--were resighted. This means the SURVIVAL RATE of that group was a MINIMUM of 47%, but could be as much as 100%, because there is no way to know what happened to the 10 birds that were not resighted. Geolocators are quite different from radio-transmitters or satellite-tracked devices that can be remotely relocated by signal receivers. Geolocators do not transmit radio signals, so birds carrying them must be resighted to determine if they survived. (The birds must be recaptured to download the geolocator's data.) If a geolocator-carrying bird isn't seen in the area being searched it isn't correct to assume that it died. It may simply be nesting a few miles away, but beyond the perimeter of the study area. With geolocators one can't simply hop in a plane and fly over a large area and listen for the appropriate ping on a receiver to refind more study birds. What the study actually showed was a 47% RETURN RATE of the geolocator-carrying birds to their previous nesting area, rather thana one-year survival rate. All things considered, being able to resight 47% of the study population a year later is pretty darn impressive. Importantly, as this was a pilot study to assess the feasibility of using newer, lighter-weight, geolocators on GWWAs, there also was a control group. Of those GWWAs that were color-banded only (no geolocators), 42% were resighted a year later. Though it's probably not a statistically significant difference, the geolocator birds actually showed a slightly higher return rate than the control birds. A return rate around 50% is quite normal for small passerine species. Finally, I want to thank Gordon, and urge him to continue his ongoing valuable service of using MOU-net to post links to interesting avian publications. There are a lot of important research findings being published every week, and Gordon does a better job than most of us keeping up with them. We all benefit from his efforts, and he probably doesn't often get thanked for doing it. Disclaimer: I am related to the lead author of this study. And I'm probably being overly nit-picky here. But I'm fascinated with the knowledge that might come from increased use of lightweight tracking devices like these. It's important to understandthat they're now so light as to be safely worn by some of our smallest birds during round-trip migrations. ---Ron Refsnider ---- Join or Leave mou-net: http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net Archives: http://lists.umn.edu/archives/mou-net.html
