There are thousands of books in the children's room at the High Bridge library, but it's hard not to notice the empty shelves. At one end of the room, where a colorful mural depicts the high arches of the nearby bridge connecting the Bronx and Manhattan and a dark green reading rug mimics a grassy hill beneath a wood and fabric tree, a bank of powder-grey metal bookshelves lines the walls, and more than half are empty. Only a few of the remaining shelves are over half full. Most contain short stacks of books and foot after foot of empty space, with an occasional title displayed facing outward.

Those shelves at High Bridge are more vacant than most, but recent budget cuts and rising circulation have made for slimmer pickings at many city libraries. Since 2002, citywide circulation has grown by nearly 60 percent, but over the last decade the number of books, periodicals and e-content materials available to circulate increased by a much smaller number – 16 percent in the New York Public Library system, which serves Manhattan, Staten Island, and the Bronx. Though rates of circulation growth varied between the NYPL and the separate Queens and Brooklyn Public Library systems, all three systems have seen major cuts to their book budgets since 2009 even as the cost of materials continues to rise.

Each budget decrease "really affects the number of items you see on the shelf," says Charlene Rue, deputy director of collection management for BookOps, a new shared division of the New York and Brooklyn public libraries that oversees the acquisition and distribution of materials for both systems.

The branches have had holes in their stacks before—in the early 1990s, the NYPL's then-president Paul LeClerc warned of a "sclerosis of the collections" after several years when funding for books plunged but circulation grew after hours of operation, which had been cut to two or three days a week at many branches, were restored to five days.

But major new factors are at play now, including technologies that are changing the ways readers access books and altering how libraries acquire and manage their collections. Books are as important as ever to libraries and their patrons – a survey last year by the Pew Research Center's Internet and American Life Project found 80 percent of Americans 16 and older consider borrowing books is a "very important" library service. But their place is evolving as they share physical space and funding with classes, community rooms, public programs and computers and other digital resources that also support libraries' broad literacy mission.

For many patrons of New York's libraries, getting any book in the library's holdings has never been easier. Others grumble about what they don't find on the shelves.

The half-full on half-empty

Emptier shelves are in part an indicator of libraries' success at getting people in the door and providing materials they want to check out. Gesille Dixon, who as library network manager oversees 16 branches in the Bronx, says she attributes the sparsely-filled shelves at High Bridge and similar ones at the Mott Haven branch to the introduction of a new after-school tutoring program in September. "Items are circulating," and as fast as they come in, they go out again, making it a challenge for staff to keep the shelves stocked, Dixon says.

Jenny Gomez, a teacher in an unaffiliated after-school program who spends hours at the Mott Haven branch each day with her students, has noticed a change since the tutoring program, an NYPL pilot, began.

"I see a lot more people grabbing books," she says. "They need them for their projects."

What's on the shelves matters to Gomez, who does all her reading at the library, where she can focus; at home her mother and two sisters usually have music playing or the television on. She doesn't check out books, and has never requested a book from a different branch library.

"I'm like the old-fashioned," says Gomez, who at 23 has been a regular at the branch for a decade. "I just look to see what kind of books I'm interested in and I read it."

The flip side of rising circulation in a time of reduced budgets is "[fewer] things are there for people to discover," says Christopher Platt, director of BookOps.

Not every branch is low on materials. Those near commercial or transit hubs, such as the New Utrecht and Dyker Heights branches in Brooklyn, or the main locations open on Sundays, like Bronx Central, tend to accumulate a surplus since they are a point for easy returns. "We have a lot of branches that are inundated with materials, says Dixon. Librarians throughout the system can "shop" for books by scouring the listings at these overstocked locations via the library's computers and have them delivered to their own branches, she says.

The libraries have what they call "floating collections," which allow books checked out at one branch to stay at the branch where they are returned, says Platt. The idea is that if one person in a community wanted to read a book, likely another will too. It's a way of "keeping shelves interesting to browse," he says.

Funds for buying new books in steep decline

Each of the city's three library systems differs in its capacity to fill its shelves. Queens has roughly 6.5 million print and digital circulation materials to fill its 62 locations. NYPL circulates roughly 5 million materials throughout 88 branches. BPL has some 3.5 million materials circulating across its 60 locations.

But for all three systems, money for new materials has been in steady and steep decline. As overall budgets for the libraries shrunk by 16 percent from fiscal year 2009 to fiscal year 2013, funds for books and digital materials were cut by more than half. QPL's materials budget was down 58 percent, from $9.65 million in '09 to $4.06 million in '13. For the current fiscal year, Brooklyn's materials budget dropped another $500,000 (or 7 percent ) from the previous year, to $6.2 million. NYPL projects it will spend about $15 million for materials this year.

"Materials is one of the very few items in our budget that the library has full discretion over, so when we have to ‘make ends meet,' that is a line that takes a hit," says Joanne King, spokeswoman for the Queens system. She says the materials budget is slated for an increase this year, to between $4.5 million and $5 million, but adds: "It could change."