One day last month, a senior conservationist at the Wildlife Conservation Society, Michael Klemens, donned waders and slogged through mud to set up turtle traps in the Bronx River. The next day, he found an energetic population of snapping turtles, ranging in age from 4 to 50.

Mr. Klemens recorded the specific details of his June 11 catch and released the animals. Along with the findings of 200 other scientists and community members who observed birds, bats, insects, rodents, plants, fungi, and fish in and around the Bronx River during a 24-hour biodiversity study. Mr. Klemens’s results were announced yesterday at a meeting of the Bronx River Alliance, an organizer of what was called BioBlitz.

According to a BioBlitz coordinator, Teresa Crimmens, the participants observed 610 species along the river, which runs for 23 miles from southern Westchester down into the East River.

Mr. Klemens said his group encountered bullfrogs, a pregnant garter snake, and a few painted turtles, but he was especially surprised to find several red-eared sliders, a species that evolved from the tiny turtles children keep as pets.

“Is the introduced species out-competing the native species? These are the kinds of questions an ecologist asks,” Mr. Klemens said. “Have we had a displacement of the painted turtle by the red-eared slider?”

A Greenway coordinator at the Bronx River Alliance, Maggie Greenfield, said her group combed the forests of the Bronx Zoo at midnight, looking for wild screech owls. The group played calls on a boom box to attract owls to their area.

The leader of Ms. Greenfield’s group, Robert DeCandido, said the number of screech owls has declined because of the use of pesticides, the felling of trees in which the owls nest, and competition with squirrels for tree space.

“They’re as much a part of our culture as the Mets and Yankees,” Mr. De-Candido, an ecologist who studies bird migration, said. “The challenge for us is to make many people aware of the good things in our parks, so if they want to protect them they can. If people are aware, they care.”

A member of the group that did the census on small mammals, Stefan Ekernas, said he caught only one white-footed mouse because animals need to acclimate to the presence of the baited cage. With more time, the group could have seen voles, shrews, or the rare flying squirrel.

“What’s interesting about the BioBlitz is that you get a little short snapshot in time and it tends to be not a complete picture,” Mr. Ekernas, research coordinator at the urban-wildlife-protection group WildMetro, said. “But it’s great to get an idea of some of everything, if not all of everything.”