Conscientious martin landlords should make a habit of regularly checking the ground underneath their martin housing for clues that may help them discover what is happening at their colony. At the PMCA's research site in Edinboro, PA, we check underneath our houses and gourds twice daily. Ground checking can be very instructive if you know how to "read" the clues you find. As a guide to help the landlord, we are publishing this primer on how to become a Sherlock Martin-Holmes.

1. Plucked feather from a nestling martin. Feathers from nestlings are only partially grown and are still enveloped in a sheath at their base. Finding a few nestling feathers is strong evidence that a baby martin was forcibly extracted from its nest cavity by an avian predator and lost the feather(s) in the struggle.

2. Molted feather from an adult martin. In late summer, adult martins begin molting their flight feathers starting with the outermost secondary on each wing. An observant landlord will often find molted secondaries on the ground under martin housing just about the time nestlings are fledging. You will rarely find more than a single molted feather on the ground at any one time.

3. Attached group of adult wing feathers. This is evidence that an owl or a hawk has taken an adult martin. Birds do not molt their feathers in attached groups. Therefore, if you find numerous individual feathers, groups of attached feathers, feathers with basal sheaths on them, entire wings, or individual feathers that are not secondaries, you have evidence that predation has occurred at your colony.

4. Wing of a nestling Purple Martin chewed off by a raccoon. Note the feather sheaths at the base of the wing. This makes it the wing of a nestling. Raccoons often eat their prey while sitting on the roof of an active martin house. After a raccoon raid, you will find entire wings on the roof of your martin house and also scattered on the ground underneath.

5. Wing of an adult Purple Martin chewed off by a raccoon. Note the absence of sheaths at the base of the wing feathers and the overall larger size.

6. Great Horned Owl feather. When owls visit martin housing at night to extract and eat martins, they often lose a few feathers in the scuffle. Look on the ground for tawny-colored, barred feathers with smooth, felt-like surfaces. Other evidence that owl predation has occurred, is finding opened or pulled-off doors on aluminum martin houses.

7. Pile of plucked nestling feathers. This is unrefutable evidence that a nestling was killed, plucked (i.e. its feathers torn off), and eaten by an aerial predator. Owls commonly pluck their martin prey at the martin housing at night before eating them. In contrast, hawks usually fly away with their martin prey before plucking them. When adult martins are eaten by owls at the colony site, the feather piles will contain feathers without basal sheaths.

8. Dead, featherless, martin nestling. Parent martins commonly remove weak, dying, or dead nestlings from their nests and drop them out onto the ground. Less commonly, starlings and House Sparrow will toss martin nestlings out while they are despoiling an active martin nest in a cavity they are attempting to usurp or takeover.

9. Two halves of a successfully-hatched martin egg. During the process of hatching, nestling martins use their eggtooth to score the inside of their egg around its equator. Upon hatching, the egg breaks into two hemispheric halves. Parent martins instinctively remove these shell hemispheres from their nest within hours of the emergence of a nestling. They usually carry them away from the colony site, but some just toss them out of the compartment hole.

10. Beak-pierced martin egg. Starlings, House Sparrows, crows, Blue Jays, and wrens will eat or beak pierce martin eggs. A beak-pierced egg will not hatch. Apparently, on occasion, martins will beak pierce their own unhatched eggs during the process of removing them from the nest.

11. Unhatched martin egg. If a martin egg fails to hatch because of infertility or embryo death, martins will often nudge them to the nest's edge. These eggs may eventually get tossed out onto the ground.

12. Runt martin egg. On occasion, the very first egg a subadult female martin lays will be of abnormal size or shape. A runt egg will rarely hatch, but if it does, the nestling would have little chance of survival, due to food competition with its larger siblings.

13. Soiled martin egg. When unhatched martin eggs are not removed from the nest cup by the parents, they become soiled from the feces of their nestmates. In those martin houses in which landlords don't clean out nests between seasons, such eggs will often get tossed out come spring when returning birds refurbish the old nests before reusing them. At such times, the ground will be littered with old eggs.

14. Shed snakeskin. When rat snakes climb martin poles to swallow eggs, nestlings, and adult martins, they will often rest for several days before descending the pole. During these periods of inactivity following a meal, they usually shed their skins. Finding shed snakeskins in, on, or below active martin housing is a good sign that snake predation has occurred.

15. Owl pellet. Several hours after an owl has had a meal, it will regurgitate a compacted pellet comprised of the non-digestible fur, bones, and feathers of its prey. If you find such a pellet under your martin housing, you'll know owls are landing on it at night.

16. Piece of corn stalk. Martins use all types of plant material for constructing their nests. Dropped material can often be found underneath martin housing.

17. Twig. During the nest-building phase of the martin's breeding cycle, it is quite common to find twigs littering the ground underneath martin housing. In most cases, these twigs are too long for the martins to get in through their compartment's entrance hole. Martins drop these twigs after futilely attempting to fit them through their cavity's opening.

18. Aluminum pulltab. Martins have the peculiar habit of carrying shiny, aluminum pulltabs into their nests during nest building. A few of them get dropped on the ground underneath martin housing.

19. Green leaf. Martins instinctively line their nest cups with fresh, green leaves. The cyanide gases given off by these leaves as they dry are thought to limit nest parasites. As the leaves dry, martins toss them out and replace them with fresh ones.

20. Metal fragments. Parent martins commonly feed their nestlings metal, glass, and quartz, which function as grit. The metal fragments shown here had passed through a nestling and were found in a nest imbedded inside a fecal pellet.

21. Glass fragments. It's quite common to find glass fragments about this size in the nests of martins, in the gizzards of martin nestlings, and on the ground underneath martin houses. Martins pick up shiny objects (such as glass and white quartz) for nest-building material and to feed their nestlings for grit.

22-33. Dropped prey items. As soon as martin nestlings are old enough to stick their heads out of their nesting holes while awaiting food from their parents, prey items start getting dropped on the ground during the food exchange. The dropped prey items pictured here were all picked up at the PMCA's research colony in Edinboro, PA. As you can see, many of these common food items are quite large.

22. Red Admiral butterfly
23. Forewing of fritillary butterfly
24. Wasp
25. Forewing of male Promethea moth. Note the beak mark on the wing.
26. Comma butterfly
27. Beetle
28. Green Darner dragonfly
29. Grasshopper
30. Mourning Cloak butterfly
31. Clear-winged Sphinx moth
32. Katydid
33. Cicada