Bird of the Month: Purple Martin
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
At nearly twice the size of other swallows, the Purple Martin is the largest swallow in the world. It flies higher than other swallows and takes months to complete its northward migration.
The male Purple Martin is a glossy dark purple swallow with a notched tail. It has wide wings that support soaring flight which can take these martins to higher altitudes than other swallows reach. The female has a grayer plumage with some white on the belly. Their shape is similar to that of European Starlings, but the flight pattern of easy wingbeats interspersed with gliding is very different from starlings.
SWALLOW OR MARTIN
Purple Martin
Scientific Name: Progne subis
Length: 8”
Wingspan: 18”
Weight: 2 oz (56 g)
AOU Alpha Code: PUMA
“The terms ‘swallow’ and ‘martin’ are used fairly interchangeably with the square-tailed species generally being referred to as martins and the fork-tailed species as swallows” (Alderfer). However, the Purple Martin is an exception and has a forked tail. Martin is from the French meaning little Mars which is a pet name (Holloway).
The Purple Martin is placed in the genus Progne, from the Greek myth about Progne who was turned into a swallow in order to escape the wrath of her husband. The specific name subis is from a Latin word used by Pliny to describe a bird that broke eagle eggs. Early American settlers placed nest boxes for Purple Martins to take advantage of their pugnacious behavior toward hawks and crows in order to keep their chicken runs safe from those predators (Helm).
NEST BOXES AND GOURDS
The Purple Martin exhibits one of the greatest geographical differences of any bird in the use of nesting sites. By1900 the North American settlers’ use of nest boxes was widespread enough that it provided alternative breeding locations for Purple Martins and helped support its population as natural cavities become scarce. Today, Purple Martins in eastern North America breed almost exclusively in bird houses (Brown, et al).
However, in the western states where the population is smaller, Purple Martins successfully breed in their traditional habitat of abandoned woodpecker holes and cavities in dead trees. In Washington, nest boxes and hanging gourds are used to provide additional nesting locations.
Both sexes build a cup nest of leaves, grass, twigs, and mud. Usually, 4-5 eggs are deposited and incubated for about two and a half weeks. Both adults feed the nestlings which fledge in a little over three more weeks.
STATUS AND DISTRIBUTION
Purple Martin populations declined severely after the introduction of European Starlings and House Sparrows into North America. Both are cavity-nesting birds which out-compete martins for suitable nesting sites. However, other factors may be impacting Purple Martins in recent years as the decline in numbers has continued.
Breeding bird survey data suggests that from 1970 to 2014 Purple Martin populations declined by 23% (Brown et al). The causes of this trend are not well known. Purple Martins subsist almost exclusively on airborne insects. In addition to the impact of a world-wide decline in insect populations, studies indicate that Purple Martins are sensitive to changes in weather and under certain adverse weather conditions will restrict their own foraging. They will not forage in temperatures below 90C (480F) or in wind speeds above 10 km/hr. (6 mi/hr.), and they do not forage in rainy weather. Other investigators have documented historical limitations on population growth among Purple Martins due to periodic severe weather-related mass death events. For example, continual rain from a stalled hurricane in late June 1972 in the eastern United States prevented martins from finding insects for days and led to a die-off of whole populations from Virginia to Massachusetts and west to the Great Lakes (Brown et al).
The Purple Martin has a wide range over the eastern United States and Canada with an extension of the range into northern Alberta. In the western United States, the range extends to limited coastal areas west of the Cascades and Sierra Nevada ranges, and delineated stretches in the mountainous regions of Colorado, Arizona, New Mexico, and Texas. It also breeds in parts of Mexico. Purple Martins spend the northern winter in central South America.
Photo credit Mick Thompson.
References available upon request from amccormick@eastsideaudubon.org.
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