Even within the same family, related species can have a vastly different appearance. One of the parts of a bird that can vary is their beaks, since the shape has evolved around their primary food source. One group that this can be seen in are finches.
Pine siskins, a small boreal finch, have thin beaks, perfect for small seeds lacking a thick shell such as thistles, grasses, alder and birch.
In the middle of the spectrum are house finches, which have a generalized shape and size for their family group. They, like their bills suggest, are general seedeaters, eating a wide variety of seeds from thistle to sunflowers, fruits, and various weeds.
On the other end of the spectrum are finches that are generally given the name of grosbeaks. This group of finches tend to have large bills compared to head size. The evening grosbeak is a good example of this. Their thich beak is perfect for larger and hard to crack seeds like box elder, ash, elms and pines. In addition, they will eat the extremely hard to crack unfallen cones of the bald cypress, few other species except the extinct Carolina Parakeet where known to also do so.