 Of the one hundred and twenty @-@ seven bird species found along the Merced River , only 35 occur along the entire length of the river . Many of these birds are migratory and only pass the area a few times every year , while 109 species of birds are found only in the breeding season . However , despite the more extensive modifications to the lower part of the river , there are more species of birds found in the lower watershed , due to the slow @-@ flowing nature of the river that forms marshes and riparian zones . Common species of bird throughout the basin include ruby @-@ crowned kinglet , cedar waxwing , American robin , yellow @-@ rumped warbler , tree swallow and European starling , and several endangered species , including white @-@ tailed kite and Swainson 's hawk . Birds that occur commonly in the middle and upper sections of the Merced River include mourning dove , Cassin 's finch , California quail , dark @-@ eyed junco , woodpecker , dipper , great blue heron , scrub jay , red @-@ winged blackbird , red @-@ tailed hawk , turkey vulture , cliff swallow , canyon wren , merganser , and rarely , bald eagle . Of the 140 insect and invertebrate species , which include mayflies , stoneflies and caddisflies , there are also three major exotic species : Asiatic clam , Chinese mitten crab , and New Zealand mud snail . 
