Since martins require lots of swooping space around their housing, a tree-encroached yard is undesirable to them. Since most fledgling martins do not return to breed at their natal colony sites, once all the veteran martins have died, the site is lost because there are no younger martins to take their place. If martin numbers at your colony site are gradually declining, and tree encroachment is the cause, only tree cutting, pruning, or house relocation will reverse the trend. If poor weather persists continuously for more than 4 or 5 days, martins begin to die of starvation. At the other extreme, heat waves and droughts can also be a problem.
Prolonged drought can also adversely affect insect numbers.
Martin landlords who allow their housing to become overrun with nest-site competitors often lose their martins. In addition, one pair of House Sparrows will clog so many compartments with their nesting material, that they essentially barricade martins from access. Research has shown that landlords who allow House Sparrows and starlings to nest in their martin housing, have colony sites with significantly reduced martin occupancy and productivity. If a landlord makes the mistake of leaving their martin housing out, and open, over the winter and paper wasps, squirrels, American Kestrels, or Screech Owls take up residence before the martins return from migration, the martins will abandon the house. A landlord should never allow any other species to occupy housing intended for martins.