Kansas City, Mo ? Bird watchers taking notice of fewer visitors to their bird feeders this winter have perhaps been left wondering why.

Well, it’s not, as some have feared, the West Nile virus, which is especially fatal to crows, blue jays and birds of prey.

It’s nothing more than the weather. The dry weather to be exact.

Seed production in plants and insect numbers are down because of extremely dry conditions in summer and late autumn, said Mark Robbins, the ornithology curator and bird expert for the Natural History Museum at Kansas University.

“Drought is affecting our counts throughout Kansas and western Missouri,” he said.

Those numbers include a decrease in sparrows as well as waterfowl, Robbins said. He has compiled numbers for recent surveys at the Squaw Creek National Wildlife Refuge north of Kansas City and the Four Rivers Conservation Area to the south, both in Missouri.

A bird count on Dec. 14 in Jackson County at several locations, including Swope Park, Lake Jacomo and Longview Lake, also showed fewer numbers of some birds, said Don Arney of Kansas City, a survey compiler for the Burroughs Audubon Society.

The limited seed crop means birds will have to go elsewhere to survive this winter, Arney said.

And that’s what’s probably causing the variations in the number of birds being seen this season as birds migrate, Robbins said. Some species may have moved to regions with more feed and water. Others may be lingering north of Kansas City because of mild weather in the upper Midwest, Robbins said.

“The blue jay you have in your yard in summer is not the same one you see at the winter feeder,” he said. “In winter, they probably come from Minnesota or Canada.”

That means birds infected with West Nile virus here likely headed south during cold spells in early December. Those arriving from the north may not have been exposed.

Mild weather, too, has kept birds well dispersed. Cold and snowy weather force birds to congregate at feeders, Robbins said.

Biologists are asking people who keep bird feeders to help track the nation’s bird populations by participating in the Project FeederWatch. Its goal is to gather long-term, regional trends for a database maintained by the Cornell Lab of Ornithology and private conservation groups.

Participants record and report bird species and their numbers at regular intervals. There is a $15 fee to participate. In return, the project provides a research kit and helps pay administrative costs.

Though not an exact science, over decades the data shows population changes or patterns for unusual bird sightings, said Larry Rizzo, a natural history biologist for the Missouri Department of Conservation.