Sadly, it sometimes happens that a landlord looses an entire martin colony from one year to the next, or so it may seem. This is often attributed (mistakenly so) to the entire flock being killed during migration.
While the martins share the same housing from year to year, they do not pal around after the nesting season. They join larger groups heading south, but do not stay in touch with each other or overwinter as a group. Your colony may have failed to re-form, or may have abandoned their nesting efforts for a number of reasons. These are some things to consider.
Predation and poor management practices
Remember, we said that martin landlords should commit the time to manage their house. This includes maintaining records of the number of young in each nest and their estimated fledge date. Why is this important? Predation is a significant reason that martins abandon their nests. Snakes, hawks, owls, cats and raccoons may all make regular visits to a martin colony. You may not notice these visits unless you are monitoring the number of young. Adult martins may abandon a nest location after only a few visits from one of these predators.
- Selecting an apartment house with apartments 12 in. deep often place the young out of reach of an owl or a hawk. Owl guards are also available.
- Barriers can be placed on the pole to prevent snakes, raccoons and others from attacking the nesting area from the ground.
Competition moves in
House Sparrows and starling can move in and take over a colony. Active management is required to evict these two species. Some apartment style houses are designed to reduce the size and shape of the entry hole, which can discourage starlings.
Be sure to clean and close the house at the end of the season. This will prevent wasps, squirrels or even Screech Owls from moving in. Martins arriving the following year will avoid houses so occupied.
If you failed to open the martin house in time, the returning martins will have moved to another location. Use the map on the attracting page to time the opening of the martin house.
Plants taking over
Keep shrubs and vines from growing up or around the base of the pole.
Also watch for tree growth bringing tree limbs and branches too close to the martin house. They may need to be trimmed back to provide 40 feet of clear fly space.
This almost sounds like a version of the princess and the pea. Martins are very sensitive to the height and orientation of their nest. If the house has been rotated significantly, or placed at a different height after inspection, the martins will become confused and may abandon the nest all together. Martin landlords with telescoping poles should mark the relative positions of the poles when lowering and raising the nests.
Martins feed almost exclusively on flying insects. They also arrive at their nesting locations early in the year. Cold snaps longer than 4-5 days will diminish inspect populations to the point that the martins will begin to starve. There is little the martin landlord can do in this situation.
On the other end of the spectrum is extreme heat. Martin houses should be designed to provide proper ventilation.
Not enough housing
A typical 'starter house' has 12 units (apartments or gourds). This is adequate to start a colony but not enough to sustain it from year to year. As many as 50% of adult martins die each year, with an even higher mortality rate in young martins. 12-15 breeding pairs are generally necessary to maintain a thriving colony.
Many apartment style housing units are designed to easily accommodate additional housing units. Gourds can also be used to expand the colony.
It was time to head south
Beginning in mid to late summer, martins will leave their nesting locations to form large staging flocks before heading south for the winter. This is normal behavior, although many first time martin landlords become concerned the first time this occurs.