Fish-eaters at Perryville

     On September 1, 2016, as I have done before, I went to the public park at Stump Point, where the Susquehanna River flows into the top of the Chesapeake Bay, near Perryville, Maryland to see what fish-eating birds were there.  I didn't notice a big variety of birds, but I did see several individuals of a few fish-eating species, including around 12 bald eagles, a dozen great blue herons, 16 or more Forster's terns, eight double-crested cormorants and several ring-billed gulls.  I also saw a half-dozen great egrets, two Caspian terns and one osprey.  All those birds of various species were interesting and entertaining to watch as they went about their daily business of getting food and resting and digesting.  And they were all post-breeding species gathering on the Chesapeake to prepare for the coming winter by gaining strength and fat reserves, as they do every autumn.
     Watching those fish-eating birds for a couple of hours, I thought about how each species catches its finny prey in various ways, and in different parts of the larger bodies of water they fish in.  That diversity of snaring victims reduces competition among them for food.  The big, magnificent bald eagles take larger fish from the surface of deeper water by swooping down and grabbing their prey with their long, curved talons from the surface, without entering the water, then pumping strongly to a boulder or tree to consume their catch, sometimes surrounded by crows and vultures who want a share of the spoils. 
     The elegant ospreys hover into the wind while watching the surface of larger waters for prey.  When a larger fish is spotted, each osprey drops to the water and plunges into it, feet first, while grasping its victim in its sharp claws.  Each osprey then uses its powerful wings to pull itself out of the water, often with a fish in its talons and powers away to a tree to ingest it.
     Interestingly, ospreys seem to be most common where bald eagles are uncommon.  There is some direct competition between those species for food.  And eagles are bigger and stronger than ospreys and often rob ospreys of the fish they caught.  
     All members of the stately heron/egret family have long legs for wading in shallow water while hunting fish of various sizes, depending on the size of each bird species.  Each member of this majestic family reaches out with lengthy neck and beak to seize fish from the shallows.  Their fishing in shallow water reduces rivalry with eagles and ospreys that usually pick up fish from deeper water. 
     The petite Forster's terns and the bulky, gull-sized Caspian terns with blood red bills fly briskly on long, swept-back wings over the water, hover into the wind momentarily, then dive beak-first into deeper water to seize small fish in their sharp bills.  They swallow their victims in mid-air while watching for more.  Obviously, terns don't rival eagles and ospreys for larger fish and they don't compete with herons for fish in the shallows.        
     Double-crested cormorants float like ducks on the water's surface and dive underwater from the surface to catch small fish.  They don't compete with eagles and ospreys because they catch little fish.  And they don't rival herons or terns by catching their prey in water deeper than those other fish-eating species can manage.
     The adaptable and abundant ring-billed gulls catch smaller fish in the shallows and the surfaces of deeper water where they compete with other fish-eating birds to an extent.  But ring-bills are also devout scavengers of dead fish of whatever size, and anything else edible.  Ring-bills also commute inland to feed on invertebrates in recently plowed fields and eat humans foods discarded by careless people on large parking lots.  While inland, of course, they are not competing with catchers of fish.   
     All these kinds of fish-eating birds fish from the same bodies of water because they ingest different sized fish that they catch from various parts of those waters.  Competition among them is reduced because of their choices of prey and the different ways of getting it.  That reduction of rivalry is another way in which the various species of life survive, indefinitely, on this planet.