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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 4. December 2012 
Identification and conservation of key habitats, 
particularly at stopover sites, may he additional 
considerations for recovering populations of 
Rusty Blackbirds (Greenberg et al. 2011). 
Additional tracking of Rusty Blackbird migra¬ 
tions from other breeding locations would further 
identify migratory linkages and important non¬ 
breeding areas tor stopover and overwintering. 
This information could test more specific hypoth¬ 
eses of the species’ decline, (e.g., the effect of 
differing migration strategics on demographic 
variables, such as overwinter survival) and be used 
to coordinate conservation across the species' 
annual cycle (Greenberg and Matsuoka 2010, 
Greenberg et al. 2011), The winter distribution of 
the species tends to vary both within and between 
years (Hamel and Ozendero! 2009. Luscier et al. 
2010). Multi-year tracking of individual Rusty 
Blackbirds could add information on the plasticity 
ot migratory movements and perhaps climatic 
events that trigger them. However, the benefits 
Irom this potential information should be carefully 
weighed against the potential harm to birds fitted 
with these devices. Only 18% of the Rusty 
Blackbirds we fitted with geolocators in 2009 
returned in 2010, much lower than the 60% of 
Rusty Blackbirds banded in 2008 that returned in 
2009 (SMM, unpubl. data). This was similar to 
differential return rates reported for Purple Martins 
(Progne snbis ; 10% return rate with geolocators, 
54% for banded only), but contrary to Wood 
Thrushes (Hylocichla mustelina: 50% return rate 
with geolocators, 33% return rate for handed only 
Stutchbury et al. 2009. 2011). Other studies that 
used geolocators to irack annual movements of 
songb.rds found return rates did not significantly 
differ between tagged birds and individuals that 
were banded and released without geolocators; e.e„ 
orthem Wheatear (i Oenanthe (tenanthe: 12 5% 
return rate with geolocators. 6.0% for banded only 
Ba,rle,„ et al. 2012), Vcery 
, retllni rate w “l» geo locators, 62% for banded 
only; Heckscher et al. 2011), Gray Catbird 
(Dumetella carotinemis ; 31.8% return rate with 
geo locators 29.9% for banded only; Ryder et al. 
-OH), and Golden-crowned Sparrow (Zonotridiia 
anu-c.pdla: 33% return rate with geolocators, 39% 
loi banded only; Seavy el al. 2012). Thus species 
may vary in suitability for this technology and 
subtle differences m harness materials and methods 
may be critical to survival success 
Al! three Rusty Blackbirds upon recapture in 
-010 had loosely fitting harnesses that had 
abraded the surrounding feathers along the 
thighs and synsacrum. Body mass was lower in 
2010 for the male and the female that wintered in 
the Western Gulf Coast Plain (by 4 and 12%. 
respectively), but not for the second female. 
Rusty Blackbirds often forage in water, which 
may have made the birds in our study more 
vulnerable to a combination of feather wear and 
reduced thermoregulation. This coupled with (he 
cold weather conditions of the 2009-2010 winter 
may have been particularly detrimental to birds 
in our study. The weight of the geolocator and 
harness we used were below 4% of body mass. 
However, we recommend future studies using 
geolocators on Rusty Blackbirds should consider 
sub-grant devices. A thorough evaluation of 
materials used for harnesses is also warranted. 
Plastic cord that could maintain a tight fit by 
accommodating seasonal changes in body mass 
could be easily damaged by Rusty Blackbirds. 
Elastic cord threaded through tubular Teflon 
ribbon (3 mm; Bally Ribbon Mills, Bally. PA. 
USA), however, may possibly produce a better 
lining harness that allows for changes in body 
mass yet is sufficiently durable. 
ACKNOWLEDGMENTS 
We are grateful to Niels Dau. Luke DeCicco. Larry 
I loarc. Russ Oates, Lisa Pajot. Marian SniveJy, Kim Trust, 
and Jen Wiley for assistance in the field. Herman Griese 
and C hris McKee of (lie Department of Defense provided 
access to study areas on Elmendorf Air Force Base and the 
US. Army s Fort Richardson, respectively. We appreciate 
Ihe helpful comments of Brad Andres. Clajt Braun. Jesse 
Conklin, and an anonymous reviewer that improved earlier 
dratl.s ul the manuscript. This study was funded by Hie 
Alaska Department ol Fish and Game's Nongame Program, 
t e U.S. Department ol Defense’s Legacy Natural Resourc¬ 
es Program, the Smithsonian Migratory Bird Center, and 
Ihe U.S. Fish and Wildlife Service. Migratory Bird 
anagement (Region 7). The findings and conclusions in 
t us article are those ol the authors and do not necessarily 
represent the views of the U.S. Fish and Wildlife Sendee. 
LITERATURE CITED 
Avi m . M. L. 1995. Rusty Blackbird (Euphagus < amlinus). 
The birds of North America. Number 200. 
Bairlpjn. F.,D. R. Norris. R. Nagfx, M. Bulte. C. C. Voict. 
J- W. Fox, D. IT. Bussell, and H. Schmauohann. 
.4)1?. Cross-hemisphere migration of a 25 e songbinl 
Biology Letters dni: 10. l()98/rsbl.20III 223. ~ 
BURGER - A - F ~ ani> S. A. Shaffer. 2008. Application of 
tracking and data-logging technology in research and 
conservation of seabirds. Auk 125:253-264. 
ESRI 009. ARCGIS. Version 9.3. Environmental Systems 
Research Institute Inc.. Redlands. California, USA. 
