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 martin numbers from the days when it nested in single pairs or small
groups.  In 2013
Partners in Flight estimated a Purple Martin population of 7,000,000,
and in 2016 the
North American Bird Conservation Initiative rated Purple Martin a
species of "Moderate Concern", with a score of 9 on a scale of 4-20, where higher
numbers indicate more concern.  At 10, the Tree Swallow score was slightly worse.

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, Eastern 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.  The photo below by David King shows a
Tree Swallow (far left gourd, just visible peeking out), an Eastern Bluebird, and a pair
of Purple martins, all wishing to nest in this group of gourds.  

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.  On the other hand, 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 and evicted 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 a martin apartment house for itself).

The Solution:  Follow this protocol for avoiding interference.
Over the years Purple Martin enthusiasts have developed some effective techniques
for reducing interspecific competition.  Excellent information can be found on the
Purple Martin Conservation Association web site, and there are a number of other
good online resources for persons concerned by bluebird and swallow competition
with martins.  The consensus is that both bluebirds and Tree Swallows must be
prevented from settling in
new or unestablished martin houses.  If these non-target
species appear to be starting to nest, 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 usually prevent others of their own kind from moving into in the nearby
martin compartments, which they consider within their own territorial space.

Here for Dan Drew's much more detailed treatment of how to prevent Tree
Swallow and bluebird interference with Purple Martin colony establishment.

The two examples below show nest sites for bluebirds or Tree Swallows placed near
Purple Martin colonies in order to reduce competition.  The first is at Doug Smith's
colony in New York.  The second, in Charlie Kelley's photo, is in Alabama.

So, if you encounter beginning martin lovers, frustrated because the "wrong swallows"
or bluebirds are claiming their new martin housing complexes, please suggest the
procedure above or recommend they contact one of the many Purple Martin hobbyist
groups or online forums for advice.

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

Learn About Birds at Tree Swallow Nest Box Projects
Reducing Competition
between Purple Martins
and Tree Swallows
bluebird/swallow box
martin gourds
swallow gourd
martin gourds