DOI: 10.5061/dryad.c59zw3rjn
title: Data from: Molt and body measurements for Gray Hawks in the Lower Rio Grande Valley of Texas

description: We captured 235 Gray Hawks (Buteo plagiatus) in the Lower Rio Grande
 Valley (Hidalgo, Willacy, and Cameron counties) of Texas from 6 February
 2003 to 8 April 2023. We identified birds in five molt cycles: 115 birds
 in their first cycle, 16 in their second cycle, 73 in at least their
 second cycle, 19 in at least their third cycle, and 12 in at least their
 fourth cycle. Of these, we documented 15 instances of preformative molt,
 six instances where birds had an incomplete second prebasic molt,
 resulting in one to three retained juvenile rump feathers and/or wing
 coverts, and 18 instances where incomplete prebasic molts resulted in
 birds with multiple generations of flight feathers. We also present
 morphometric data from 144 Gray Hawks (nestlings and first-cycle birds
 captured prior to 1 October excluded). These results from the Lower Rio
 Grande Valley, on both molting strategies and measurements, differed in
 some respects from other sources based on the entire Gray Hawk population,
 most notably that birds from this northern and non-migratory population
 may show lower incidence of Stafflemauser molting patterns, and that they
 are heavier, which supports Bergmann’s rule.
description: We primarily used bal-chatri traps with 8–10 cm nooses made from
 13.6 kg test monofilament fishing line to capture free-flying Gray Hawks
 (Bub 1991). We also used phai traps, bow net, and mist nets with a mounted
 Great Horned Owl (<em>Bubo virginianus</em>) lure near nest
 sites (Bloom et al. 2007). We fit Gray Hawks with individually numbered
 U.S. Geological Survey (USGS) aluminum bands, and birds banded after
 November 2019 also received an aluminum color band (Acraft Sign and
 Nameplate Co. Ltd., Edmonton, Alberta, Canada and Anillas Talismán S. L.,
 Madrid, Spain). We recorded hallux claw length, tail length, mass, wing
 chord, and exposed culmen length for each bird (Hull and Bloom 2001, Pyle
 2008). Measurements were obtained using digital scales and calipers, clear
 plastic rulers, and metal wing rules with a 90-degree stop following the
 techniques outlined in Pyle (2008). We did not measure tarsus length
 because this was too difficult to standardize among multiple
 banders. Measurements on 196 birds were performed by WSC or MTS, with ten
 banders performing measurements on the remaining 39 birds under their
 direct supervision. We initially categorized birds as
 in their first year (juvenile or formative plumage) or as adults (basic
 plumage) based on the criteria of Pyle (2008). We also categorized birds
 as actively molting flight feathers or not molting. First-year birds
 were examined for preformative molt, i.e., newer gray formative
 body feathers contrasting with juvenile feathers. Preformative molt occurs
 prior to the onset of the second prebasic molt, as documented and
 discussed for Gray Hawk and other raptors in Pyle (2005a). Adults were
 examined for retained, worn, brown juvenile or moderately worn, gray,
 basic flight feathers. We ensured that our findings were based on molt by
 examining replacement patterns on both wings, and not
 adventitious replacement, which is not symmetrical between
 wings.  We categorized molt and plumage cycles using
 Humphrey-Parkes-Howell terminology, and age classes according to
 molt cycle (Howell et al. 2003, Clark and Pyle 2015, Pyle et al. 2021). We
 separated age classes into local (nestlings, unable to fly), first cycle
 (between fledging and dropping the first primary during the second
 prebasic molt, or HY/SY in calendar-based terms), second cycle (between
 this and dropping the first primary during the third prebasic molt, or
 SY/TY), minimum second cycle (AHY/ASY), minimum third cycle (ASY/ATY) ,
 and minimum fourth cycle (ATY/A4Y). When examining flight feathers, we
 looked for “sets” of sequentially replaced feathers between distally
 oriented waves<br>of molt (Pyle 2006, 2008). Sets are defined by an
 older, more worn primary distal to an adjacent newer primary, each set
 showing a cline in freshness from older inner to newer outer
 feathers, although a cline may not be even due to differing generations
 or molt suspensions; the number of these sets was used to
 determine minimum age for birds beyond third cycle (Pyle 2006,
 2008). Open-wing images showing front and back of an extended wing were
 taken for archival purposes and to study molting patterns.
description: # Data from: Photos and banding data from: Molt and body measurements for
 Gray Hawks in the Lower Rio Grande Valley of Texas
 [https://doi.org/10.5061/dryad.c59zw3rjn](https://doi.org/10.5061/dryad.c59zw3rjn) ## Description of the data and file structure From 6 February 2003 to 8 April 2023, we captured 235 Gray Hawks, 201 newly banded birds and 34 recaptures of previously banded birds. We categorized molt and plumage cycles using Humphrey-Parkes-Howell terminology, and age classes according to molt cycle (Howell et al. 2003, Clark and Pyle 2015, Pyle et al. 2021). We separated age classes into local (nestlings, unable to fly), first cycle (between fledging and dropping the first primary during the second prebasic molt, or HY/SY in calendar-based terms), second cycle (between this and dropping the first primary during the third prebasic molt, or SY/TY), minimum second cycle (AHY/ASY), minimum third cycle (ASY/ATY) , and minimum fourth cycle (ATY/A4Y). When examining flight feathers, we looked for “sets” of sequentially replaced feathers between distally oriented waves of molt (Pyle 2006, 2008). Sets are defined by an older, more worn primary distal to an adjacent newer primary, each set showing a cline in freshness from older inner to newer outer feathers, although a cline may not be even due to differing generations or molt suspensions; the number of these sets was used to determine minimum age for birds beyond third cycle (Pyle 2006, 2008). Open-wing images showing front and back of an extended wing were taken for archival purposes and to study molting patterns. ### Files and variables 48 color photographs of Gray Hawks showing the extent of molt. Birds that molted flight feathers include the USGS band number in the file name, those with preformative molt include the color band two-digit code and color in the file name. Two R scripts for running summary statistics and creating tables. One csv file with banding data. Missing values are indicated by "NA." * Band - newly banded or recapture * USGS band number * Banding date - in day-month-year format * Year * Color band - includes the leg the color band is on, right (R) or left (L), along with the color of the band and the two-digit code * Latitude - of banding location * Longitude - of banding location * Age - calendar based age codes * Local (L) * Hatching Year (HY) * After hatching Year (AHY) * Second Year (SY) * After Second Year (ASY) * Third Year (TY) * After Third Year (ATY) * After Fourth Year (A4Y) * After Fifth Year (A5Y) * Plumage category - this describes the plumage of the individual * Sex - male (M) or female (F) * Hallux - in millimeters * Tail - in millimeters * Mass - in grams * Wing chord - in millimeters * Culmen - in millimeters * Molt - if the bird was actively molting, had evidence of a preformative molt, or exhibited Staffelmauser * Comments ## Code/software Analyses were performed using R, and with the following packages: * tidyverse * here * knitr * kableExtra * sjstats * sjPlot