3 of the 4 birds shown are Red Crossbills. The fourth (lower right image) is a Black-Headed Grosbeak. All of the birds have very interesting oversized bills but the Red Crossbills have an additional feature: a curved almost clawlike tip on their upper bill. This tip assists them in a very specific type of foraging. These Crossbills eat pine seeds and that bill allows them to pry the seeds out to eat while the seeds are still in the cones.The Black-Headed Grosbeak's bill is thick and strong for breaking open seeds but isn't nearly as useful in getting food directly from the cones. The Red Crossbills beak gives it a little jump on the competition.
Red Crossbills, like the Williamson's Sapsucker we saw earlier, exhibit plumage dichromatism. Males are bright red and females are a duller yellow. The bird in the lower left corner is probably a juvenile male, showing bright yellow with splotches of red. This bird will likely become all red as it matures.
