Hello Bird Nerds On page 525 of the Sibley Guide to Birds (Pine Grosbeak account) and page 513 (Red-winged Black Bird account) there are illustrations of plumage variations in those species that are denoted by two female symbols or two male symbols. Why is this? Do such double symbols indicate an unusual genetic sorting? Could this occur in all passerines? Is this a printing error? I have seen photos of the Black Bird variation and observed what Sibley calls "Russet" female Pine Grosbeak variation in Northern Minnesota. I am quite curious as to what this symbolism means.
Alex Watson ---- Join or Leave mou-net:http://lists.umn.edu/cgi-bin/wa?SUBED1=mou-net Archives:http://lists.umn.edu/archives/mou-net.html
