Feather macrostructure corresponds to increased temperature not urbanization across California

Urban environments are often associated with resource and environmental differences, providing potential novel selection pressures compared to adjacent unmodified landscapes. While these characteristics (e.g., heat islands, reduced vegetation) can contribute to differences in certain behaviors, morphology, or physiological traits, there is mixed evidence on how and to what extent populations are responding. In this study, we compared the feather morphology of Dark-eyed Junco (Junco hyemalis) populations established across an urbanization gradient. We examined whether differential temperature regimes, related to urbanization, correspond with significant variations in the proportion of down. We sampled ventral and dorsal feathers from 256 individuals throughout central and southern California at varying degrees of urbanization. Dorsal feathers had a higher proportion of down compared to ventral feathers, but did not differ between populations. Urbanization did not significantly correlate ..., We captured 256 Dark-eyed Juncos across central and southern California during the 2022 (n = 47) and 2023 (n = 209) breeding season (February–August) between 07:00 and 12:00. We mist netted at six locations on average per day, and at each location, the net was open for 30 min during which playbacks were used to attract juncos in the area. Playbacks consisted of singing juncos from Los Angeles. We color-banded each junco with a unique three-color band and one USGS aluminum band combination and recorded various metrics as part of a long-term study. Metrics included bill dimensions (width, depth, and length), body weight, wing chord length, tail length, and tarsus length. We quantified sex differences based on the presence of brood patch or cloacal protuberance, as well as plumage characteristics. The juncos were aged as after second year (ASY), second year (SY), after hatch year (AHY), or hatch year (HY) based on known plumage and molt limit. Data from HYs and recaptured juncos were exclu..., , # Feather macrostructure corresponds to increased temperature, not urbanization, across California

[https://doi.org/10.5061/dryad.1jwstqk3t.](https://doi.org/10.5061/dryad.1jwstqk3t)

Comparison of feather macrostructures (plumulaceous barbs and pennaceous barbs) found in dark-eyed juncos. Temperature values include the mean, minimum, maximum, and range from 1991 to 2020, as well as from 2021 to 2022. Built-up Index (BU) values were presented based on average values within a 50m radius around the banding site and calculated as the difference between NDBI and NDVI. 

Relevant morphometrics per individual are also included, and the federal band number is listed.

## Description of the data and file structure

The dataset consists of data files: dorsalfeather.csv and ventralfeather.csv. Standard morphometric values are provided and measured in (mm), except weight, measured in (g). Federal band numbers and band colors are included, as well as site metrics. \"Eumelanin Proportion\" refers to ...,