Warm weather early in the year means rattlesnakes are more active than usual following April's breeding season, and local dogs could be bearing the brunt of it, animal experts said.

"Our calls are up -- calls on dogs bitten, dogs dying and quite a few people bitten," said Al Wolf of the Sonoma County Reptile Rescue Center in Sebastopol. "By the end of May, we're usually at about 25 rattlesnakes; this year we're at 85 already."

PetCare Veterinary Hospital in Santa Rosa has seen a 30 percent increase in rattlesnake bites affecting pets this year.

"We had twice as many bites in April compared to last year, and it's really unusual," said Dr. Nicholas Davainis. "We also saw some much earlier in the year, even one in January."

Carolyn Cole-Schweizer, who lives near Annadel Heights above Bennett Valley, lost her Jack Russell terrier to a rattlesnake bite early this month. The terrier discovered a rattlesnake in the backyard and suffered three bites in the leg before dying of the injuries.

"We've been there (in the house) two years, but we've never had one," Cole-Schweizer said. "We don't know why the rattlesnake came into our yard."

The rescue center knows of at least three dogs that have died from rattlesnake bites this spring, but the number could be higher, Wolf said.

Wolf attributed the increase to the weather, noting the past decade has been marked by sporadic local weather patterns. Davainis also said warmer weather could have contributed to the increase.

Though Wolf said he knew of one Cazadero woman who suffered a severe rattlesnake bite requiring a longer hospital stay, local emergency rooms haven't seen any significant increases.

A Kaiser Permanente spokesman reported one person who was treated for a rattlesnake bite over the past few months. The individual was briefly admitted and then discharged. Sutter Hospital spokeswoman Lisa Amador also reported one snakebite from April.

Santa Rosa Memorial Hospital's emergency room has treated one person for a rattlesnake bite over the past two months, hospital spokeswoman Katy Hillenmeyer said.

The California Poison Control System reported a decrease in rattlesnake bites statewide this spring.

"We've had reports of about 66 bites so far, but that's somewhat low for us," said Stuart Heard, executive director of the California Poison Control System. "Although last year we did have a big increase in calls."

Heard also said that Poison Control is "just one part of the picture" among the many agencies who receive calls about snakebites, and said that the number could be higher.

"It's always important for people to be alert," said Heard.

Wolf said Northern California is lucky in that it only deals with one species of rattlesnake -- the Northern Pacific rattler.

"Southern California has around seven different species of rattlesnakes," Wolf said. Several of those species' venom contain more toxic proteins or neurotoxins that can affect the nervous and respiratory systems, making their bites trickier to deal with, he said.

If people discover a rattlesnake on their property, people should back away from the snake and call the rescue center, Wolf said.

"Once you see it, you're safe," Wolf said. "Give us a call and we'll come get it -- that's what we're here for."

You can reach Staff Writer Melody Karpinski at 521-5205 or melody.karpinski@pressdemocrat.com.