Supplementary material for Striking rusty-brown neck collars in Rufs: plumage polymorphism or staining? Yvonne I. Verkuil, Joop Jukema, Pavel S. Tomkovich, Nelli Rönkä, Jos C.E.W. Hooijmeijer & Theunis Piersma Corresponding author: yvonneverkuil@gmail.com Tis PDF contains: Fig. S1. Seasonal patterns in the recording of the intensity of the rusty-brown neck collars in the staging population of Ruffs in Friesland, The Netherlands. Table S1. Model selection to determine factors involved in the occurrence of rusty-brown neck collars in Ruffs migrating northward through Friesland, The Netherlands. Fig. S2. Seasonal change in the occurrence of rusty-brown neck collars in Ruffs in the staging population in Friesland, The Netherlands. Fig. S3. The single female amongst 73 females in Zoological Museum of Moscow State University showing a possible trace of the rusty-brown neck collar. Fig. S4. Iron oxide test results for rusty-brown feathers collected from the neck of Ruffs, with negative and positive controls. research paper Wader Study 128(1): supplement. doi:10.18194/ws.00223