TONY CROASDALE, a heavily tattooed bird-watcher/punk-rocker from South Philly, was leading a Saturday bird walk in November on a wooded trail along Cobbs Creek when Wendy Willis, a high-school student in the Cobbs Creek Environmental Center's naturalist training program, said, "I see a yellow bird."

Croasdale, a high-octane dude who brings the headbanging energy of his defunct thrash band R.A.M.B.O. to birding (imagine going on a bird walk with Iggy Pop) remembers thinking, "Goldfinch."

He peered through his high-powered binoculars.

"I'm stunned," Croasdale recalled recently, standing on the fateful trail. "I've birded all around the world and I've never sounded the alarm on a mega-rarity before. I sounded the alarm."

The yellow bird was a Townsend's warbler, a Pacific Northwest species that should have wandered no farther east than the wilds of Montana. Apparently blown off course, it was hanging out on Naylors Run trail, a ribbon of creekside woods between the rowhouses of Upper Darby and West Philly.

Fifty serious birders responded to Croasdale's alarm. "The bird hung out all weekend, which was cool," Croasdale said.

But a mega-rare warbler showing up thousands of miles from home wasn't the coolest thing that happened. The bigger miracle was that people were on a trail in Cobbs Creek Park to see it.

After decades as a crime-ridden, overgrown haven for torched cars, trashed appliances and the occasional body, Cobbs Creek Park has been exorcised of its gruesome ghosts.

And its transformation is a shining example that last year's merger of the lethargic Fairmount Park Commission and the city Recreation Department - which the Daily News' Pulitzer Prize-finalist "Acres of Neglect" campaign advocated for a decade ago - was the right thing to do.

Park rebirth

Cobbs Creek Park's spectacular makeover puts it on the verge of becoming Philadelphia's next hot recreation oasis.

But first, Parks and Recreation Commissioner Michael DiBerardinis has to convince thousands of neighbors on both sides of Cobbs Creek - many of whom use the five rec centers on the park's perimeter but won't venture into the interior - to hike, run or bike the nearly seven miles of trails, or just spend some quiet time in the woods.

"Connecting the Cobbs Creek neighbors to the watershed," he told the Daily News, "is the first big test of whether the merger is working. There is no comparison between the use of Cobbs Creek Park and the use of Wissahickon or Pennypack parks. Cobbs Creek's beauty is in the same league. What's missing are the people."

Working their butts off to get the people back into Cobbs Creek Park are folks like Joe Caesar - a Parks & Rec volunteer coordinator who is equal parts spiritual visionary and sweat-equity grunt.

As he walks the born-again Cobbs Creek trails, showing off what he, 30-year park-system veteran Harry Clement and their 1,000-volunteer army have done, Caesar, 49, is nearly overcome with emotion.

"The older growth was there, but you see that whole under-forest?" Caesar asked, pointing to hundreds of leafy young trees reaching toward the sun. "The kids restored that under-forest by hand. They removed the jungle of invasive Japanese knotwood, and planted silver maples, river birches, white oaks and sycamores. So you're looking at a hand-planted forest canopy."

Fish and turtles flourish in the creek. During mating season, Caesar said, "you hear bullfrogs out here nonstop."

Near the end of one trail, you can see the city but you don't feel it. Instead, you feel the Cobbs Creek peace.

"I have to slap myself sometimes when I look at all we've done," said Caesar, who started out as a Cobbs Creek Park community liaison in 1998. "This was a burned-out dump. Only the bold and the seriously delinquent ventured in here. Both trails were closed - so overgrown you couldn't walk them, so dangerous you wouldn't want to."

He said professional studies concluded that Cobbs Creek Park would always be that way.

"The research said there was such a long history of dumping and neglect here that the community was turned off," he said as sunlight filtered through the young forest along the trail. "So the problem was, how can you get people back on board when you've turned your backs on them for decades?"

Some years back, Caesar and Clement rounded up some neighborhood teenagers and started cleaning out the massive garbage dump at the park's Marshall Road gateway, removing the thick walls of invasive plants, opening the creek trail that had been closed since before those kids were born.

But since the Parks & Rec merger, that work has accelerated at breakneck pace - supported, as always, by the Pennsylvania Horticultural Society, which donated the lion's share of the trees, shrubs and flowers.

"We had over 1,000 volunteers here in 59 days this spring," Caesar said joyously. "Everything from church groups to the Jewish Federation of Philadelphia's 'Mitzvah Mania' day of service. I'm surprised I'm still standing. If you find any body parts in the woods around here, they're mine."

Beauty on a budget

The throngs of volunteers and DiBerardinis' world-class partnering skills have enabled cash-strapped Parks & Rec to make Cobbs Creek Park look like a million bucks for less than 50 grand.

"When I was here the first time, I was loaded with capital dollars," said DiBerardinis, who served as rec commissioner under Mayor Ed Rendell. "Now, I have 1/20th the money."

So DiBerardinis connected with revitalization-minded partners including the Philadelphia Water Department, which is pouring $150 million over the next 10 years into restoring the creek, and into building an extensive pipe system to prevent sewage from overflowing into it during storms.

And he's partnering with the Ed Snider Youth Hockey Foundation, which is spending millions to enclose three ice rinks - including Cobbs Creek Park's Laura Sims Skatehouse - as year-round rec centers.

DiBerardinis said: "I'm not the kind of person who says, 'These are tough times. We've got money troubles. We'll just sit back and wait until the recession's over.' Even in tough times, you can do big things if you connect with partners who want to do them."

Cobbs Creek Park is running a full slate of new programs - biking, birding and photography clubs, family movie nights - to dispel the lingering fear that it's unsafe. The greater the neighborhood presence in the park, DiBerardinis said, the safer it will be.

He said that Philadelphia police are working with their counterparts in Upper Darby and Millbourne to eliminate "legitimate safety concerns such as crazy ATVs [all-terrain vehicles], drug use, drinking, homeless encampments - the kind of stuff that keeps people out of the park."

Neighbors take pride

That kind of nonsense, plus the dumping of burned-out cars and appliances along Callowhill Street near 67th, is what used to make the northern section of Cobbs Creek a nightmare, said Kesho Watson, who led the neighbors' effort to turn the mess there into the beautiful tree-lined meadow, picnic area and creek trail that it is today.

Watson and her neighbor, Sylvester Melvin, whom she dubbed "the unofficial cop of Cobbs Creek," keep a watchful eye on their piece of the park.

"There's a calmness here," Watson said, but it takes constant vigilance by a network of park-loving residents with cellphones. "We text when something's going on. The police are very responsive."

On the Upper Darby side of the park, Joe and Betsey Piette, like their Philly counterparts, grew sick of the invasive shrubs that created a hidden haven for drug users and muggers, and the Fairmount Park Commission's "let it return to its natural state" credo of neglect.

"I'd walk my dog along the park and see other women walking their dogs, carrying a baseball bat or a golf club for protection," Betsey said. "We are a multinational neighborhood of Irish, Greeks, African-Americans, Asians, Eastern Europeans - and we came together over common concerns. At our first cleanup in 2008, 40 neighbors came out with everything from machetes to kitchen tools, we cleared that first block along the park from Chestnut Street to Afton Road and just kept going."

Today, the park's border is a welcoming gateway accented by neighbor-tended garden beds.

"Before, ethnic differences might have kept people from talking to each other," Betsey said. "Working together has broken down a lot of barriers, besides making our park beautiful."

Betsey, an accountant, loves gardening and bird walks. Joe, a postal worker, is a runner. "I'd drive to the Art Museum all the time to run," he said. "Now, I run in Cobbs Creek Park from Callowhill Street to Baltimore Avenue. That's a five-mile loop."

Betsey said: "For years, Cobbs Creek was the stepchild of the parks system. Not anymore."

"What we are doing in Cobbs Creek," DiBerardinis said, "is a model for what the merged Parks and Recreation Department can do all over the city. So we have to do this one right. We're doing this one right."