Molt and body measurements for Gray Hawks in the Lower Rio Grande Valley of Texas

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 no..., 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 (Bubo virginianus) 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 b..., , # 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, w...