The Problem: Tree Swallows can prevent establishment of Purple Martin colonies.
You may encounter persons hoping to attract Purple Martins who complain Tree
Swallows are interfering with their plans.  We've added this page so you can direct
them to online resources which explain in depth just how to resolve this problem.  
But before discussing this subject you might want some Purple Martin background.  
(The photo below by Cathie Westcot shows a perching female Purple Martin and a
Tree Swallow peeking out of a martin "gourd" house).





















Don't be fooled by the name; Purple Martins are swallows.  The term "martin" comes
from England, where swallows with short, squared or notched tails are traditionally
called martins, as opposed to "swallow-tailed" species such as Barn Swallows.   

Purple Martins are our largest swallows by far, weighting nearly three times as much
as Tree Swallows (56 gm. average as opposed to 20 gm.).  The bird on the left below
is a male in full adult plumage.  At right is an adult female.




















Purple Martins are obligate secondary cavity nesters, meaning that they must nest in
cavities but are unable to make their own.  Under original (pre-human) conditions
Purple Martins relied on old woodpecker holes and natural cavities in trees and large
cacti.  These sites are still used by martin populations in Mexico, and the United
States and Canada west of the Rocky Mts.  However, martins in eastern North
America now nest exclusively in cavities provided by people.  These houses can be
quite elaborate, with multiple compartments of varying sizes and shapes, and a large
hobbyist movement has grown up dedicated to attracting colonies of Purple Martins.





















Purple Martin colony projects, some with hundreds of nesting pairs, have
dramatically increased the numbers of this species from the days when it nested in
single pairs or small groups, and today Purple Martins appear to be in excellent shape,
with a population of about 11,000,000 and a rating as a species of "Least Concern" by
the International Union For Conservation of Nature and Natural Resources (IUCN).

Why have eastern martins switched to such an unnatural, concentrated mode of
nesting?  One factor may be that "martin houses" now vastly outnumber the old, hole-
filled riverside snags Purple Martins once preferred.  Plus, concentrations of cavities
have favored certain martin behavior, especially the willingness of older, experienced
males to permit younger males to settle nearby, allowing the older males
opportunities to father more young by copulating with the younger martins' mates.















However, it should come as no surprise that concentrations of cavities put out for
Purple Martins attract other cavity nesting species, among them European Starlings,
House Sparrows, bluebirds, and Tree Swallows.  These four species begin nesting
before martins arrive in spring, and all four will defend their nest and surrounding
compartments against martins.  These martin competitors pose somewhat different
levels of problems for martin lovers.  Starlings and House Sparrows will harass and
drive away adult martins, break their eggs and kill their young, but since they are
unprotected non-native birds starlings and sparrows can be dealt with aggressively.  
But, bluebirds and Tree Swallows are natives whose active nests cannot be
destroyed legally by humans.  Luckily, these native species do not destroy martin
eggs and young, and pairs that try to nest in well-established Purple Martin colonies
are normally dominated easily by returning martins.  However, if a pair of bluebirds or
Tree Swallows has begun nesting in one compartment of a new or unestablished
martin site they will try to defend the entire housing complex against other birds,
which discourages Purple Martin "scouts" from settling at the new locale. (In the
photo below by Ryan Bloom the "wrong swallow" has claimed an apartment house).

















The Solution:  Follow Dr. Daniel Drew's protocol for avoiding interference.
Over the years Purple Martin enthusiasts have developed some effective techniques
for reducing interspecific competition.  The Purple Martin Conservation Association
web site is one excellent resource, but the best reference for persons concerned by
bluebird and swallow competition with martins is Daniel Drew's very detailed page on
the subject.  Dr. Drew states that it is essential that bluebirds and Tree Swallows be
prevented from settling in new or unestablished martin houses.  If these non-target
species appear to be starting, all martin compartments should be closed at once or
the houses completely removed temporarily.  A single nest box built to the smaller
birds' specifications should then be erected no more than 25' to 35' away from the
martin site (see below), with its entrance facing the martin houses.  The pair of
bluebirds or swallows should be allowed to occupy this box, but only when there is
evidence they have truly committed to it (nest building and egg laying) should the
martin houses be reopened.  Once committed to the single box the bluebirds or
swallows will prevent others of their own kind from moving into in the nearby martin
compartments, which they consider within their own territorial space.


















So, if you encounter martin lovers frustrated because the "wrong" swallows or
bluebirds are investigating or claiming compartments in their martin housing
complexes, please refer them to Dr. Drew's web site for assistance.

And if by chance you find both Tree Swallows and Bluebirds are interested in your
martin houses try "pairing" two swallow/bluebird boxes 5-10 feet apart from each
other, with the box pair 25-35 feet away from the martin compartments.  You might
hit the jackpot and have all three species nest!  For more on pairing boxes for
swallows and bluebirds click here.







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Learn About Birds at Tree Swallow Nest Box Projects
Martin Competition
bluebird/swallow box
martin houses