Task: Question Generation
Input (English): Passage: After European colonization, the passenger pigeon was hunted more intensively and with more sophisticated methods than the more sustainable methods practiced by the natives. Yet it has also been suggested that the species was rare prior to 1492, and that the subsequent increase in their numbers may be due to the decrease in the Native American population (who, as well as hunting the birds, competed with them for mast) caused by European immigration, and the supplementary food (agricultural crops) the immigrants imported (a theory for which Joel Greenberg offered a detailed rebuttal in his book, A Feathered River Across the Sky).  The passenger pigeon was of particular value on the frontier, and some settlements counted on its meat to support their population. The flavor of the flesh of passenger pigeons varied depending on how they were prepared. In general, juveniles were thought to taste the best, followed by birds fattened in captivity and birds caught in September and October. It was common practice to fatten trapped pigeons before eating them or storing their bodies for winter. Dead pigeons were commonly stored by salting or pickling the bodies; other times, only the breasts of the pigeons were kept, in which case they were typically smoked. In the early 19th century, commercial hunters began netting and shooting the birds to sell as food in city markets, and even as pig fodder. Once pigeon meat became popular, commercial hunting started on a prodigious scale.Passenger pigeons were shot with such ease that many did not consider them to be a game bird, as an amateur hunter could easily bring down six with one shotgun blast; a particularly good shot with both barrels of a shotgun at a roost could kill 61 birds. The birds were frequently shot either in flight during migration or immediately after, when they commonly perched in dead, exposed trees. Hunters only had to shoot toward the sky without aiming, and many pigeons would be brought down. The pigeons proved difficult to shoot head-on, so hunters typically waited for the flocks to pass overhead before shooting them. Trenches were sometimes dug and filled with grain so that a hunter could shoot the pigeons along this trench. Hunters largely outnumbered trappers, and hunting passenger pigeons was a popular sport for young boys. In 1871, a single seller of ammunition provided three tons of powder and 16 tons (32,000 lb) of shot during a nesting. In the latter half of the 19th century, thousands of passenger pigeons were captured for use in the sports shooting industry. The pigeons were used as living targets in shooting tournaments, such as "trap-shooting", the controlled release of birds from special traps. Competitions could also consist of people standing regularly spaced while trying to shoot down as many birds as possible in a passing flock. The pigeon was considered so numerous that 30,000 birds had to be killed to claim the prize in one competition.
Output (English): What did commercial hunters start to net and shoot in the early 19th century?