DOI: 10.5061/dryad.zs7h44j9s
title: Feather corticosterone reveals developmental challenges in a long‐term study of juvenile northern spotted owls

description: 1. Corticosterone is a steroid hormone integral to a variety of
 physiological pathways and is strongly associated with the vertebrate
 stress–response. In avian species, circulating corticosterone is
 sequestered into developing feathers and is used as an indicator of energy
 allocation during feather growth and widely applied in conservation
 physiology. 2. The northern spotted owl (Strix occidentalis caurina) is a
 federally threatened old–growth forest obligate of conservation concern
 endemic to the Pacific Northwest of the United States and Canada. The
 effects of landscape characteristics and individual variation on early
 development in spotted owls remain unstudied despite long recognition of
 this knowledge gap and its potential importance to species conservation.
 3. We quantified corticosterone concentrations in 4,720 feathers from
 1,056 juvenile spotted owls across seven study areas between 2001 and
 2017. We used an information–theoretic approach to examine the
 environmental and individual factors related to feather corticosterone in
 juvenile spotted owls as an indicator of challenges during early
 development. 4. Feather corticosterone was positively related to
 temperature and precipitation, and negatively related to juvenile mass at
 banding. We found strong support for an interaction between mass and
 precipitation, with greater amounts of precipitation being associated with
 higher levels of feather corticosterone in lighter juveniles. The
 temperature and precipitation metric with the strongest relationship with
 feather corticosterone occurred during the fledging period, suggesting
 that this period presents an energetic challenge for juvenile spotted
 owls. Greater juvenile mass decreased the effect of precipitation,
 suggesting that greater mass was important for juveniles to maintain
 homeostasis during fledgling. 5. Feather corticosterone in juvenile
 spotted owls provided insights to the challenges faced during early
 development, adding to our understanding of spotted owl life history and
 potential for population recovery.
description: Crews monitored historic spotted owl territories annually between
 15 March and 31 August 2001–2017, capturing and banding fledged juveniles
 for individual identification. During banding observers collected contour
 feathers from the belly, breast, back, and head of juveniles and stored
 them in plastic bags at room temperature (19 – 22° C). Sample collection
 was opportunistic and to minimize harm to owls, the area of the body and
 number of feathers collected varied by natural feather loss, but 4–12
 contour feathers was typical. All feathers were fully grown at the time of
 collection. To minimize potential bias, we standardized
 feather CORT values by total sample mass (picograms CORT per milligram of
 feather). We used radioimmunoassays to estimate corticosterone in feathers
 between 5–90 mg total mass. Five percent of the samples were greater than
 90 mg and were divided into two or three parts of approximately similar
 mass. Nearly all feathers were entirely or mostly plumulaceous.
 Following the protocol established by Bortolotti <i>et
 al.</i> (2008), we removed each calamus, measured along the rachis
 to the nearest mm, and then weighed each feather to the nearest tenth of a
 milligram. We cut the feather into pieces less than five mm<sup>2
 </sup>and placed them in 20 ml test tubes with 7 ml of
 high-performance liquid chromatography grade methanol (VWR
 International,<i> </i>Radnor, Pennsylvania). We placed samples
 in a sonicating water bath at room temperature with a cap to limit
 evaporation for 30 minutes and then moved them to a shaking water bath at
 50° C overnight. We used individual 23 cm disposable glass Pasteur
 pipettes to transfer each sample extract to 14 ml test tubes and rinsed
 the original feather sample with an additional 3.0 ml of methanol for two
 hours and that was added to the sample in the 14 ml test tube. We dried
 each sample under an evaporator rack with pressurized air in a water bath
 at 40° C. We reconstituted the dried samples in 250 ml of buffer solution,
 vortexed the samples, and then refrigerated them overnight. We then
 aliquoted the samples into duplicate 5 ml tubes and performed
 radioimmunoassays following manufacturer’s instructions (MP Biomedicals,
 LLC; Immunochem<sup>TM</sup> Double antibody Corticosterone
 <sup>125</sup>I RIA Kit, Cat. No. 07-120103), except we used
 half-volumes. We used a parallelism test of two pool samples sequentially
 diluted 1:1 (20% binding) to 1:64 (90% binding) to ensure samples fell
 within the quantitative range of the assay and that our feather mass was
 adequate to achieve ~ 50% binding. Both samples were parallel to a
 standard curve and a 1:4 dilution was adopted. Inter-assay coefficient of
 variation was 9.2% across seven assays and intra-assay coefficient of
 variation was 1.9%. For samples that were subset and used to estimate
 extraction variation, we used the mean feather CORT for subsequent
 analyses<i>.</i>
description: For the health and safety of some owls, they were released prior
 to obtaining a mass measurment. These owls were populated with the study
 area specific means. Description of Data within
 NSOfeatherCORT. ID: Individual ID number that is
 specific to a different owl in the data set<br> Collection Year:
 Hatch year fo rht e owl in which feathers and other data were
 collected<br> NN: Nest number that is specific to territory and year
 to account for auto-correlation of nest mates, but also broods from
 previos years of the same adults on the same territory<br> MASS:
 Mass in grams recorded during banding<br> mCORT: designated as mean
 CORT for any owl that had enough feathers collected to subset into
 multiple samples. Otherwise denotes the corticosterone (picograms/mg
 feather) extracted from a feather sample.<br> lCORT: natural
 lo-g-transformed corticosterone<br> STUDY: The study area on which
 the juvenile was reared<br> rBO: range-wide average annual
 proportion of historic spotted owl terriories in which a barred owl was
 detected at least once on territories surveyed three or more times within
 the breeding season.<br> xBO: Study area specific annual proportion
 of historic spotted owl terriories in which a barred owl was detected at
 least once on territories surveyed three or more times within the breeding
 season.<br> PPT 1-7: Annual study area specific mean of daily
 precipitation (mm) in 8 different 2-week periods: 1: April 10–April 23; 2:
 April 24–May 7; 3: May 8–May 21; 4: May 22–June 4; 5: June 5–June 18; 6:
 June 19–July 2; 7: Jul 3–July 17; 8: July 18–July 31<br> Tmean 1-7:
 Study area specific mean of daily mean temperatures (°C) in in 8 different
 2-week periods: 1: April 10–April 23; 2: April 24–May 7; 3: May 8–May 21;
 4: May 22–June 4; 5: June 5–June 18; 6: June 19–July 2; 7: Jul 3–July 17;
 8: July 18–July 31<br> Meas: The number of known years a juvenile’s
 father had occupied a territory, considered their number of breeding
 seasons of experience at a site.<br> Feas: The number of known years
 a juvenile’s mother had occupied a territory, considered their number of
 breeding seasons of experience at a site.<br> NR FOREST: The
 proportion of 30 x 30 m pixels in a juvenile’s natal territory covered in
 forest designated as suitable for nesting/roosting in the year they
 hatched.