What specific field mark helps differentiate modern North American *Pica* species like Black-billed and Yellow-billed?
Answer
Bill color
When observing present-day species like the Black-billed and Yellow-billed magpies in North America, the text indicates that subtle field marks are necessary for differentiation. Specifically, paying close attention to the color of the bill is mentioned as a key way to distinguish between species that share the common 19-million-year-old ancestor. While iridescence of tail feathers is also noted as a distinguishing feature for the lineage generally, bill color is explicitly provided as a means to separate the North American counterparts mentioned.
Related Questions
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