From PCT Online, November 2009:

“In May, a small group of professionals from around the country met the “locals” from one of the toughest rodent environments — New York City. Here’s a bit of what they learned…

“New York City was established in 1625 as New Amsterdam. No one knows for certain when the rat arrived thereafter, but estimates place it at perhaps 150 years later. Now, the problems associated with keeping rat populations low in New York City are directly related to New York’s human population….

“So, how will New Yorkers manage this formidable pest within the constraints of this complex city? The cold, hard truth is, in spite of the best efforts of NYC pest professionals, the Norway rat is likely to persist there in the shadows and underfoot, out of sight and mind to most except those that seek it out. They’ve had more than two centuries and hundreds of generations surviving and adapting to life in the Big Apple. In fact, it’s fair to say that most rats in New York City are not killed by man. Most die from stress caused by competition for food and territory among their own kind….”  Read more at: http://www.pctonline.com/Article.aspx?article_id=42946