Where Do Birds Go To Molt Their Feathers?

This adult male northern cardinal (Cardinalis cardinalis) has a less-than-spectacular appearance because he is molting. This study suggests that northern cardinals, which are resident, still move to molt — although only by a short distance.
(Credit: Keith / Creative Commons Attribution 2.0 Generic license.)
FIGURE 1. Bird-capture stations used in breeding and molting probability analyses. Dots indicate distribution of 936 Monitoring Avian Productivity and Survivorship (MAPS) stations and dashed lines indicate delineation of western and eastern North American regions for analyses.
(doi:10.1642/AUK-17–201.1)
FIGURE 2. Captures of breeding and molting birds in relation to day of year. Birds in breeding condition peaked in June–July, while birds in molting condition were largely captured in July and August; no substantial differences in these patterns were noted between West and East regions.
(doi:10.1642/AUK-17–201.1)
FIGURE 4. (A) Predicted probabilities that landbirds captured at their breeding sites would also be captured molting. Dashed lines show mean species predicted molt probabilities; shaded regions span ±95% credible intervals. The mean probability that a bird captured at its breeding site would be molting was similar in the West (0.47; 95% cred. int.: 0.38–0.57) and East (0.42; 95% cred. int.: 0.32–0.52). Six species showing evidence for directional or elevational movements to molt are illustrated. (B) Boxplots summarize distributions of predicted molt-probability means for species categorized according to the literature as nonmigratory (Resident; shown in black), migratory and reported to molt on the breeding grounds (Breed; shown in blue), or migratory and reported to molt away from the breeding grounds (Nonbreed; shown in orange).
(doi:10.1642/AUK-17–201.1)
FIGURE 8. Examples of spatial (latitude and longitude) and elevational shifts from breeding to molting locations for selected species. Sample sizes are given for each species. Maps were developed by implementing 1° resolution, spatial–conditional autoregressive models with responses representing differences between probabilities of captured individuals being in breeding condition during May–August and being in molting condition if captured on August 1. Bluer areas represent relatively high breeding probabilities relative to molting probabilities; redder areas represent relatively high molt probabilities relative to breeding probabilities. Breeding locations aggregated within 1° cells are indicated with black “x” symbols; molting locations are indicated with black open squares; symbol sizes are scaled according to numbers of captures in breeding or molting condition, respectively. Locations in which all captures lacked both breeding or molting condition are shown with gray open circles scaled to total numbers of captures. Latitude, longitude, and elevation plots represent differences in each response variable (mean ±95% confidence intervals) between stations where birds were captured in molting relative to breeding condition.
(doi:10.1642/AUK-17–201.1)
Although most migrant landbirds showed southward and/or eastward movements between breeding and molting grounds, Steller’s jay (Cyanocitta stelleri) showed an unusual northward movement to its molting grounds.
(Credit: Alan D. Wilson / CC-BY-SA 3.0.)

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𝐆𝐫𝐫𝐥𝐒𝐜𝐢𝐞𝐧𝐭𝐢𝐬𝐭, scientist & journalist

𝐆𝐫𝐫𝐥𝐒𝐜𝐢𝐞𝐧𝐭𝐢𝐬𝐭, scientist & journalist

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PhD evolutionary ecology/ornithology. Psittacophile. scicomm Forbes, previously Guardian. always Ravenclaw. discarded scientist & writer, now an angry house elf