So curious I overrode my aversion to HTML in titles. Quote of note:

Joseph J. Salvo, the population director for the New York City Department of Planning, had yet another theory. The migrants, he surmised, might be prison inmates. To that end, Mr. Salvo explained that, according to the census, 99 percent of these new Bronx residents were living in institutional group quarters, a category that includes prisons. Nearly 90 percent of them arrived in the Bronx, he said, to Community Districts 1 and 2, which includes Rikers Island. Furthermore, almost all of them were men. It looks like a prison population transfer, he went on, but quickly added that there were not enough state prisons and holding facilities in Allegany County to account for more than 4,000 people. He mused aloud that it was conceivable that inmates from other upstate counties might have accidentally been counted in the mix, although he could not tell for sure.

Exodus Lacks Explanation on Trail of Bronx Mystery By ALAN FEUER ANDOVER, N.Y., Nov. 10 - William Bosworth, a retired professor at Lehman College in the Bronx, made an odd discovery a few years ago while studying the latest census data. Much to his surprise, he determined that from 1995 to 2000 about 4,000 people moved to the Bronx from rural Allegany County, in the southwest corner of New York State. This was strange. Allegany County, nestled in the woodlands along the Pennsylvania border, is as country as the country gets and has as much in common with the Bronx as a barnyard has with Billy's Sports Bar outside Yankee Stadium. The county covers more than three times the area of New York City, but with a population of only 49,950. In Allegany, people fish, drive pickup trucks and hunt deer come fall. It is sometimes said that folks in Allegany County would not move next door to Cattaraugus County. So why would 4,000 of them suddenly pick up and migrate to the Bronx? Dr. Bosworth, who used to teach political science and now runs the Bronx Data Center at Lehman, did not have a clue. "I got the data and looked at it three times to make sure I wasn't misreading it," he said. "But there it was. You understand, I'm not making this up. It's in the census." Still, he included a disclaimer in his findings, which he put on a page of his Web site, called "Discovering the Bronx," (www.lehman.cuny.edu/deannss/bronxdatactr/discover/bxtext.htm). "The large migration to the Bronx from little Allegany County is a mystery not yet explained," he wrote.