Diurnal Raptor Enemies of Purple Martins
(by Kent Justus)
A small group of adult Purple Martins circles slowly above their colony site.
They have just returned after hunting for a few hours far away from their gourds
and houses. The martins want to return to their housing to rest before venturing
out to feed again. They have recently migrated back to their breeding site after
a long and treacherous journey from the South American country of Brazil. The
martins circle lower and then as a group they slowly descend to the houses and
gourds. Suddenly, before the martins realize that they are in danger, a bird
appears in their midst that is scarcely larger than they are. The bird has a
very long tail and short, rounded wings. Panic ensues and martins scatter in
all directions emitting loud cries of alarm. The enemy bird has singled out
a mature male Purple Martin for pursuit and has rapidly closed the gap. Suddenly
it seems that the two birds are separated by only a couple of feet and the martin
begins to weave from side to side with the enemy right on his tail all the while
losing altitude until now very close to the ground. The enemy bird not only
mirrors the evasive actions of the martin, but seems to anticipate them. Suddenly
long legs are thrust forward from the enemy bird and needle sharp talons close
tightly around the martin. Their momentum takes the birds to the ground and
the enemy bird stands with the martin clutched tightly in its talons. The martin
emits a plaintive call and tries to struggle but the talons only squeeze tighter.
The other martins have now returned to witness the struggle and a few of the
mature males are dive bombing the enemy as they realize the fate of their flock
member. The struggle ceases from the martin and the enemy bird now stands victoriously
over its prey. The enemy bird then rises in flight and carries the dead martin
into the nearby forest where it is plucked and eaten. The enemy bird's identity
is revealed as the swift and cunning Sharp-shinned hawk.
I observed the above scenario unfold in March of 1992. It's hard to imagine the sleek and swift Purple Martin having enemies that could be capable of catching them on the wing but this is exactly the case under certain conditions. Adult Purple Martins are among the largest members of the swallow family (Hirundinidae) and are capable of great speed in flight when necessary. However, their bodies are shaped for flight in the open skies and when flying at low altitudes below the tree canopy they are vulnerable to attack by bird catching raptors such as accipiter hawks and small falcons. The long, angular wings that allow martins to attain high speeds high above the ground are not designed for quick acceleration. Also, recently fledged martins are on the menu for even more species of raptors such as kites and harriers.
Accipiter
hawks are probably the deadliest of the diurnal (daytime) raptor enemies of
adult Purple Martins. There are three species of accipiters in North America:
Sharp-shinned, Cooper's, and Goshawk. The Sharp-shinned hawk is the most common
and is about the same size as a Mourning Dove. The Goshawk is the largest, about
the size of a Red-tailed hawk. It is mainly a bird of the northern forest and
is rarely seen by humans. The Cooper's hawk is intermediate in size between
the Sharp-shinned (or Sharpie) and the Goshawk. It is about the size of a small
crow and has a very wide breeding range across North America. In addition, their
population seems to be increasing. Accipiter hawks are the sprinters of the
hawk world and have relatively short, rounded wings and a long tail. The legs
are thin and extremely long and equipped with sharp talons. Accipiter hawks
kill their prey with their talons and the more the prey struggles, the tighter
the talons close around their victim piercing vital organs. The spasmodic gripping
of the talons is called footing. (Photo: adult male Cooper's
hawk. Younger birds are much lighter underneath).
Out of this group the Sharpie is the most dangerous to Purple Martins. While its top speed is not quite as fast as the Cooper's hawk, it can accelerate much quicker and also has awesome reflexes and agility when pursuing small birds at close quarters. The Sharpie can also stoop from a great height right into the midst of a martin colony and go relatively unnoticed until dangerously close because of its very small size. With wings completely folded it is scarcely larger than a martin and can surprise the martins this way in addition to ambushing them from nearby trees. My good friend Victor Stoll and I have both witnessed this type of attack. The Cooper's hawk seems to be less adept at catching adult martins than the Sharpie but it is still deadly, especially to fledglings. Mr. Stoll, who lives in Finger, Tennessee and Steve Kroenke of Tallahassee, Florida have both witnessed several attacks by both species on their large martin colonies over many years and concur that the Sharpie is more dangerous to adult martins than the Cooper's. The Cooper's hawk is also notorious for landing on martin houses and extracting martins through the entrance holes. I have never heard of them attempting this on gourds. The Goshawk is probably not a serious threat to adult martins as its larger size makes it less maneuverable than the smaller accipiters. It would have a harder time sneaking up on martins without being noticed due to its large size and it usually targets larger prey.
When faced with a deadly chase by a Sharpie or Cooper's hawk below the tree canopy Purple Martins are usually at a disadvantage because the hawks can accelerate to their top speed in a matter of seconds and their long tails make them incredibly maneuverable. Accipiters try to catch fast flying birds such as martins, swallows, and swifts in a quick surprise attack at close quarters. They will not pursue fast flying birds for very long distances unless they are targeting a fledgling. Once adult martins gain speed they usually escape from accipiter hawks and above the tree canopy the odds turn dramatically. Purple Martins can fly circles around any accipiter hawk up high in the air and readily attack and mob the accipiters which seem to lack any speed or power the higher up they fly. Accipiters won't even attempt to pursue adult martins high in the air but will sometimes still go after fledglings. The fledglings can still escape from them if they can outclimb the hawk to a safe altitude.
Following is an observation by Steve Kroenke of a Sharp-shinned hawk attack
on a male martin: "It was early March and my colony had been tormented
for over a week by a female Sharpie and a female Cooper's hawk. The colony for
all practical 
purposes
ceased to exist and the martins no longer stayed at the houses and gourds during
the day. One day I was patrolling the perimeter of the colony waiting for one
of the hawks to attack any martin that had not yet left the site. Suddenly,
a male martin bolted from his gourd, gained speed quickly and streaked upward.
He was not more than thirty feet high when the female Sharpie exploded from
a tall nearby pine tree and met the martin head on. The martin violently turned
downward and the Sharpie matched the move. The martin twisted and turned from
side to side while the Sharpie followed every move. The martin then pulled up
abruptly in a vertical climb that took him about forty feet high. The Sharpie
also climbed and was only a foot or two from the martin's tail, but the martin
was slightly faster and the Sharpie stalled out. Then the martin, emboldened
by his successful escape, immediately attacked the Sharpie and mobbed the hawk
as she flew into the nearby forest." (Photo above:
mature Sharp-shinned hawk).
The second group of diurnal raptor enemies of adult Purple Martins would include falcons such as the Peregrine, Prairie, Merlin, and American Kestrel. Obviously this group contains some of the fastest and highly celebrated fliers in the bird world. Falcons are birds of the open skies and are built for sustained flight with long, pointed wings and body shapes configured for maneuvering at speed. It would seem that Purple Martins would appear in the diet of these falcons more than they actually do based on the fact that foraging flocks of martins often come into contact with hunting falcons. Why are very few martins caught by falcons? The answer is simple: falcons tend to hunt in the open sky above the tree canopy. This just happens to be the arena where the Purple Martin's own remarkable flying ability is at its peak. The martin's combination of speed and supreme aerial ability usually render it superior to a pursuing falcon. When falcons are successful at catching fast flying birds such as martins it is usually by surprising them by stooping from a great height rather than by outflying them in a tail chase. Tom Cade is a nationally recognized falcon expert and author of the book "Falcons of the World". I heard from Mr. Cade a couple of years ago and he told me that swallows and swifts are among the most difficult targets for falcons to capture in open flight.
Even the Merlin, a small falcon which is noted for its swift and tenacious pursuit of small birds, seems to be overmatched against the Purple Martin in open flight. Merlins usually have little difficulty in capturing their chosen targets but Steve Kroenke has witnessed over a dozen extended pursuits of adult Purple Martins by them, none of which was successful. Following is his account of a Merlin pursuing an adult female martin: "I was watching my colony one morning when the predator alarm went off and the martins headed for the sky. A small, tight flock of martins was climbing at a terrific rate of speed when suddenly the martins seemed to explode in different directions. A Merlin had flown directly into the flock! The Merlin was going at full speed after a female martin. Both birds were literally "on fire" as the race of life and death continued at full steam. The Merlin matched the martin's level flight speed and closed in for the kill. The martin banked quickly to the side and the Merlin overshot but then turned around and continued the chase. The martin adeptly dodged each attack while gaining altitude at the same time. Within seconds the martin had outclimbed the Merlin and had joined other members of the colony which were preparing a counter attack. The Merlin dived quickly away with a flock of angry martins on its tail". Steve tells me that while the awesome speed of this particular chase wasn't measured, it seemed that the birds were flying at about 60 miles per hour. Martins have been clocked at 41 miles per hour while feeding but could almost certainly fly much faster than this when confronted with a deadly chase by a falcon high in the air.
The Merlin, Peregrine, and Prairie falcons pose the greatest threat to adult Purple Martins but the robin-sized American Kestrel can also cause problems. A Minnesota resident (our very own Linda Janilla!) informed me that she had witnessed the capture of a martin this year by a female kestrel which was nesting nearby. The kestrel attacked the martin as it flew from the top of a tree slamming into it and riding it all the way to the ground. The kestrel then managed to fly away with the martin while being fiercely mobbed by other martins.
Other diurnal raptors that are potential threats to Purple Martins include
the Mississippi Kite and Northern Harrier. These aren't as fast or agile as
the accipiter hawks or falcons but can still pose a serious threat to fledglings.
My own colony in central Arkansas 
is
attacked every year by Mississippi Kites when the young martins begin to fledge.
The daily attacks occur most frequently in early afternoon and the falcon-like
kites tail-chase and stoop at the fledglings until they tire them out. The young
martins that have been flying for only 1-3 days are at greatest risk because
they haven't developed any flying stamina. I watched a fledgling get caught
this year after dodging at least seven different attacks by the kite but then
as it tired, it could no longer maneuver with very much speed. As the fledglings
reach about day four the odds begin turning in their favor and after about seven
days of flying they can easily escape the attacks and the kites no longer even
attempt to pursue them. They can recognize how old the fledglings are by their
flight style and always target the inexperienced fliers. Even then their success
rate at capturing them is not very good. The young martins escape the kites
by rapidly changing direction when the kite closes in on them. The kite's method
of attack in open flight makes it conspicuous to the martins which emit loud
alarm calls and are rarely caught off guard. (Photo:
Mississippi Kite).
In conclusion, there are many species of hawks and falcons that will prey on
Purple Martins when given the chance. Let me point out again, however, that
adult martins are usually only vulnerable to daytime raptors under certain conditions.
The size of the martin colony and it's proximity to large trees seem to be the
major factors in attracting bird catching raptors. From my experience, the larger
the colony, the more likely it is to be attacked. This is especially true when
the colony is encroached by trees. While some martin colonies are attacked frequently
and on a yearly basis, daytime raptors probably account for only a very small
percentage of the annual mortality of the entire Purple Martin population. What
then, you might ask, is the most dangerous raptor enemy of martins? Listen for
the haunting calls of the Great-horned and Barred owls and you will have your
answer. - Kent Justus - Little Rock, Arkansas
