Birds don’t always look like they do in field guides.

There are variations within a bird species due to obvious reasons such as age, time of year or sex. Immature birds take time to achieve adult plumage. That could be a few months or, in the case of the bald eagle, four or five years. Male wood ducks, one of the most splendid birds in New England during breeding season, is a dull brown duck after shedding its breeding feathers. Sexually dimorphic birds, such as cardinals, have obvious differences between males and females.

Sometimes, even the sun can make birds look different. Grackles may appear purple, green, blue or black, depending on how the light hits it. Male indigo buntings can look spectacular or rather ordinary depending on the sun.

There are also regional differences among bird species. Blue jays in New England, I have found, are much brighter and larger than the blue jays in Florida. I’m also surprised when I see how small the blue jays are when I visit my brother in southern Florida.

Some bird species have different morphs. Most of the red-tailed hawks in New England are lighter overall than their western counterparts. This is also commonly referred to as a phase. The best example of a morph I can think of is not a bird at all, but the gray squirrel. Gray squirrels also come in white and black. In fact, in some parts of the country, black gray squirrels are the norm and gray ones are the rarity.

Then there are the pigment abnormalities such as albinism, leucism and melanism. Albino birds are fairly rare. Albinism is a condition that prevents the production of melanin, which is the pigment that gives animals their color. Leucism, or partial albinism, is more common. It is still extremely unusual to find a leucistic bird. Robins, juncos and red-tailed hawks seem to be particularly susceptible. I remember seeing a pair of leucistic Canada geese many years ago. They were more white and tan rather than brown and black.

Melanism causes birds to look darker than their “normal” kin. Again, red-tailed hawks seem to be susceptible to melanism. Red-tailed hawks, with their morphs and light and dark pigment abnormalities, definitely do not always look like their picture in the field guide.

Hybridization also impacts the bird world and can make for difficult identifications. Mallards and black ducks often hybridize, making for a duck that looks an awful lot like a mallard, but something is off just a bit. Other ducks and gulls hybridize as well. Oddly enough, there are also many cases of hybrid hummingbirds seen in the West.

A bird’s diet can also impact their appearance. The carotenoids in the algae eaten by the tiny shrimp gobbled up by flamingos give the large birds their pink appearance. With that algae and shrimp, flamingos would appear gray instead of pink.

In New England, sometimes people see an oddly colored house finch. Most male house finches are reddish pink, but every once in a great while, people will see an orange or yellow house finch. This is because the bird’s diet during the molt did not contain the pigments of a house finch’s typical diet that give the birds their normal color.

Finally, sometimes birds look different for unknown reasons. With an estimated 50 billion individual birds in the world, some strange occurrences are bound to happen. I have yet to hear a good explanation as to why some downy woodpeckers appear to be yellow or tan and black instead of the usual white and black. It could be the diet or could be that the inside of the hole in the tree that it calls home rubs off the plumage, but I’ve only seen this in one bird at a time. I would think the bird’s mate would have the similar abnormality.

Who knows? Maybe it was something it ate.