Purple martins congregate at one of the bird houses in Memorial Rose Garden on Monroe Street Tuesday after their first sighting in the city this week, normally a harbinger of spring’s arrival. According to the Purple Martin Conservation Association Web site, the purple martin, the largest member of the swallow family, has specific aerial space requirements. Housing should be placed in the center of the most open spot available, about 30 to 120 feet from human housing with no trees taller than the martin housing within 40 feet. Purple martins spend the non-breeding season in Brazil, then migrate to North America to nest.(The Vicksburg Post/MELANIE DUNCAN)