Why do you find some plants and animals in one place and not another, while others seem to be everywhere? It depends on the needs and competitors of the creature or plant in question.
Let’s start with a bird that seems like it is everywhere: the Common Grackle. They hang out in parking lots looking for french fries! Surely they can tolerate anything. They do have preferences, though.
If you live in a more rural area and don’t have the extensive green lawns and food-filled parking lots, grackles are actually quite an unusual sight. I was excited to find one in “the wild” once, singing over a marshy lake edge. Its iridescent purple and bronze plumage was quite beautiful.
If they weren’t so common I suspect people would be searching for them eagerly!
All species have preferences based on their needs, but how picky they are varies. Ducks need water, but diving ducks (like Buffleheads and scaup) want deeper water, while dabbling ducks like Mallards, pintails and Gadwalls will hang out in shallow areas where they can dip their heads down to forage in the mud.
Red-tailed Hawks like to have trees or power poles from which they can watch for prey, while Red-shouldered Hawks prefer to hunt in more wooded areas.
Even plants need certain nutrients and have particular moisture requirements, so certain species will be found on certain soil types, be that clay, sand or loam.
The endangered Golden-cheeked Warbler requires mature ashe juniper forests because it will only use strips of its bark in its nest. Woodpeckers need dead trees to excavate nest cavities.
Sometimes the habitat preference can change depending on the season, perhaps because they need one habitat for nesting but are less picky in the non-breeding season.
Sometimes competitors can restrict where an animal or plant will live. Young oak trees can grow in the shade and will sprout up under a canopy of hackberries, but young hackberries can’t stand shade. Thus new hackberries will die once the oak forest becomes established.
Competition can be a problem with introduced species. For example, European Starlings nest in cavities like woodpeckers but use holes that are already excavated. This results in some woodpeckers losing their homes to birds that they are not adapted to compete with.
It can be a fun bird-watching (or anything-watching) experience to track where you see different species and how it varies by the seasons and years. A good example is Golden-crowned Kinglets.
Those tiny birds are usually not very common; we tend to see them in areas with larger trees, like in wooded ravines. This year they are very common and almost in all forested areas. Field Sparrows are fairly common all winter in any brushy habitat, but then in the summer they disappear to only a few places.
As far as I can tell, chickadees and cardinals are in the same areas year round.
The abundance of hawks seems to vary with the rodent population.
Often times we will notice the presence or absence of particular birds but have a hard time figuring out why they are gone. This is influenced heavily by factors at the population level, not just a local effect, which is why it is so hard to say why a particular bird is not around much some years.
One would need to look at environmental influences across the whole range to figure out if a species is in trouble or just locally gone for the short term. This is what many bird-monitoring programs do. These include Project FeederWatch (http:/www.birds.cornell.edu/pfw/), Breeding Bird Survey, Christmas Bird Count and eBird (www.ebird.org).
Both FeederWatch and eBird are particularly accessible because they occur over the whole winter and year round, respectively, and offer us a chance to contribute our observations to studies of bird populations.
Whether you are counting birds, feeding birds or casually observing them on your way home, keep your eyes peeled for the associations between your favorite critters and where they live. You never know what you will learn about the interactions that shape nature!