CITY HALL -- D'oh deer.

Only 527 deer were found on Staten Island during the city's latest aerial survey of the herd -- 236 less than the last count two years ago and well below what the city expected.

The Parks Department insists that the data will nonetheless play a crucial role in plans to perform hundreds of vasectomies on borough bucks to help manage what is still believed to be an expanding herd.

The city only looked for deer on Island parkland in 2014 -- the most recent survey this past February was of the whole borough.

"We had to redo it because this is not a plan to manage deer in parks in Staten Island, it is a plan to manage deer in all of Staten Island," said Sarah Aucoin, Chief of Wildlife and Education at Parks.

A low-flying plane piloted by a wildlife biologist used infrared technology to map concentrations of deer during the two surveys. Both were done in mid-February and cost less than $20,000 each.

Results of two deer surveys of Staten Island in 2014 and 2016. The 2014 survey was only of the borough's green space, while 2016 looked at the whole Island.

Officials said fewer deer could have been found this year because the survey was done during warmer, less cloudy weather than in 2014. Infrared picks up less on clear days and deer may have been more skittish in higher temperatures.

"When you have a warmer winter, people are using the parks more," Aucoin said.

The city would have to repeatedly survey Staten Island over several months to get a more precise aerial count.

"There's nothing to indicate that the population has declined -- we are confident that it doesn't mean that," Aucoin said. "What this means is we've got a minimum of 527 deer on the Island, but it's likely much higher."

The city has no official population estimate of Staten Island's herd, though many ecologists believe there could be more than 1,000 deer here now. The 2014 survey found 763 deer in borough green spaces.

The Parks Department will spend $2 million this year to sterilize male deer as part of a three-year study. The plan is expected to eventually reduce the borough herd 10 to 30 percent annually.

The city hopes to glean a more accurate count of deer after the first part of the study.

'NUMBER OF DEER IS LESS IMPORTANT'

Wildlife conservation nonprofit White Buffalo Inc. will not only perform the vasectomies, but will track deer with ear tags, radio collars and trail cameras. The data will be independently analyzed by other wildlife biologists who are experts in population modeling.

This year's survey shows large concentrations of deer in the Greenbelt, most parks and along the West Shore. But many deer are also in residential parts of the city.

"We knew that they were venturing outside of parks and into other areas, but it confirmed what we suspected," Aucoin said.

Though Parks officials were initially concerned about the survey results, they don't think an exact count is vital.

"The deeper you get into deer management, the more you learn that ultimately the number of deer is less important and what's most important is how they are affecting people and what do people want to do about it," Aucoin said.

HOW DEER AFFECT PEOPLE

An unrestrained and expanding deer herd can harm parks and private property, spread tick-borne illness and wander into roads more often, increasing the risk for deadly vehicle collisions.

The bacteria that causes Lyme disease was found in about a third of 107 deer ticks tested by the city in 2014. The NYPD has reported 26 deer-vehicle collisions on Staten Island so far this year, on track to surpass a total 40 in all of 2015.

The city believes the herd is growing mostly through reproduction, not migration onto the Island. Sterilizing males instead of females is meant to be faster, cheaper and more humane.

Some wildlife experts think the plan won't work because the city is ignoring basic deer biology and conventional herd management practices. A few called the proposal "really stupid" and "incredibly foolish."

The state Department of Environmental Conservation regulates wildlife and must approve a control plan. Fertility control is only permitted by the state as part of a scientific study.

THE VASECTOMY PLAN

Anthony DeNicola of White Buffalo is expected to start performing vasectomies in September, in time for this fall's rutting season.

So far DeNicola has walked the entire Island and identified 104 properties where he can reach the greatest number of male deer. Most are parks or city property, but a few are private developments.

The Island's been divided into four research zones where the biggest bucks will be targeted for vasectomies first. They'll be baited, shot with tranquilizers and driven unconscious to one of several parks facilities that would be prepped for the surgery. The deer would then be released where they were caught.

The plan is unprecedented in scope and method.

"We're really venturing into new territory," Aucoin said.

This article was corrected to clarify that the vasectomy effort is expected to eventually reduce Staten Island's deer herd 10 to 30 percent annually, not 10 to 30 percent overall.