Using Porch Dividers On Purple Martin Houses And Houses With Separate Porches Per Hole
Purple martins are colonial nesters and nest in concentrated numbers in gourd racks and houses. Though martins nest together, they are still territorial to an extent and seem to “like a little space” between nesting pairs—territorial privacy.
Before purple martins became colonial nesting birds, they probably nested as single pairs or scattered pairs in abandon woodpecker or natural cavities in dead trees. This nesting behavior encouraged martins to develop territorial defense behaviors to protect their cavities from other martins. Martins out west still nest in natural cavities.
As martins transitioned to nesting in cavities provided by people, including natural gourds and wooden houses, martins became more communal nesters. And with this gradual change, martins began fighting each other over territory and mates.
Some martins are overly aggressive and the males in particular will take over multiple cavities to keep other males out. This is called nest domination behavior. I have seen one male martin dominate an entire side of a traditional Trio aluminum house with six rooms per side and not let any other male martins move in.
Why do some martins try to control multiple cavities in a martin house? This behavior relates to territory and mate selection. Some aggressive males try to keep other males out so that the male “owning” the territory has a better chance of attracting a female without more competition from other males. Plus having multiple cavities gives any female a choice for a nest site and it’s the female that selects the male and his territory. Nest domination behavior tends to most severe during territory establishment, mate selection, and nest building. Once a female has finished nest building and started laying eggs, then her aggressive mate may begin to relinquish control of vacant cavities near their actual nest site and other new males can move in.
Some purple martin houses will have multiple compartments per floor with holes side by side. This means that entrance holes share a common porch and martins can move at will along the porch and control multiple cavities. A good example of these is the traditional 12 room Trio house with three holes per floor and six holes per side.
Fortunately there are commercial martin house designs that now incorporate one entrance per floor providing territorial privacy and others that have porch dividers. Some examples of aluminum houses include the Trendsetter, Sunset Inn, Lone Star Goliad and Alamo (much like a wooden T-14) and Coates Watersedge. I have used all these houses in my various martin colonies. The most well-known wooden house is probably the T-14 with vertical placement of rooms and separate porches.
Other commercial martin houses where cavities share a common porch can be modified by the landlord with either factory supplied porch dividers or homemade ones. We, my next door neighbor and I, have modified traditional Trio M-12s and Castles with porch dividers in our personal martin colonies and satellite sites in northwest Louisiana. These changes have increased occupancy levels by martins in these colonies.
Why are porch dividers important? These dividers can serve two main functions and can increase martin occupancy levels and even help to successfully fledge more youngsters.
First, a porch divider separates entrance holes on a continuous porch and can help to reduce male martins from dominating multiple cavities. The porch divider helps to keep a male from easily moving on a continuous porch and minimizes visibility between entrances. However, aggressive males can still go around these porch dividers and chase off other male martins. But the dividers can help to reduce dominating behavior.
Second, the dividers can prevent large martin nestlings from moving along the porch and entering nests of other martins which may contain eggs or babies. When large nestlings move into other occupied nests, the non-parental martins will usually attack and try to evict the interlopers. If the larger nestlings invade a nest with smaller babies, the invaders, if not evicted, will often consume most of the food. This can sometimes result in the smaller nestlings starving or becoming malnourished. So dividers can help prevent this problem on houses with continuous porches and the martins are nesting closer together.
What about separate porches per entrance hole? This design approach serves to isolate each cavity from others and help provide territorial privacy. Plus nestlings are unable to move along a continuous porch to enter other cavities. However, aggressive martins can still dominate by moving up, down or to the side from one porch to the other. But the separate porch design may minimize this behavior or reduce the duration of it as the breeding season progresses.
If you don’t want to use a multi-room house and perhaps have to modify it, then the easiest solution is a gourd rack with a cluster of gourds! Gourds tend to provide more territorial privacy between martin pairs as each gourd is separate from the others. Plus nestlings can’t move along a common porch to enter different gourds. Gourds can be arranged on a rack so that the entrances face different directions and visibility is reduced between martin pairs. I have always had greater occupancy levels in gourds over houses in my various martin colonies in north Florida where I previously lived and now in northwest Louisiana. However, aggressive martins can still control multiple gourds but such domination behavior in gourds tends to be less severe and doesn’t last as long as with houses. And I’m currently replacing my remaining Trendsetter houses with gourd racks. For the 2020 martin season I will only have two Trendsetters left in my martin colony and my plan is to go all gourds in 2021. Though I had good success with my Trendsetters and other modified aluminum houses with porch dividers, I have always preferred gourds over houses and will finally go that route in the future.
However, other martin landlords have excellent success with properly designed martin houses such as T-14s with vertical placement of rooms and separate porches and Trendsetters with staggered entrances and one hole per floor with porch dividers. Both separate porches and/or porch dividers can increase occupancy levels by martins and minimize problems with large nestlings moving from one nest to another. Modifying quality houses such as the Trios with porch dividers may increase their occupancy levels and eliminate nestlings moving from one cavity to another.
Here are some photos of houses where I installed porch dividers. There is a 16 room Lone Star Goliad that already has by design separate porches. However, I installed homemade porch dividers on this Goliad to create even more territorial privacy between martin pairs. Another photo shows two Trio M-12s with factory installed porch dividers. These houses are on a multi-purpose pole with four Troyer Horizontal gourds. The Trio is a traditional martin house where rooms share a common porch. In this house, there were three rooms per side with enlarged compartments. Both houses and all the gourds were usually fully occupied by the martins each season. The last photo shows a Trio Castle that I modified with double nesting chambers and porch dividers. This castle was always 100% occupied by martins.
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