Richard and Diane Van Vleck Personal Pages The Home Habitat |
Purple Martins’ use of clam shells in the 2018 nestingSmall clam shells were gathered from the nesting material in last year’s martin nests. The shells were disinfected and offered to this year’s colony, as well as the usual ground oyster shells. 6/30/2018 – Looking out an upstairs window in the early morning, I saw what appeared to be an ASY male martin passing a small object to a female. They were perched on the calcium supplement tray under their gourd rack 100 feet from the house. Looking through a 19th C wavy glass window sash at that distance, a speck of white is all I could see. But, a tray of twenty small clam shells of the genus Corbicula had been placed in the tray the previous evening. The possibility of seeing this behavior repeated up close and with a camera prompted me to set out trays of clam shells and observe from the wagon shed. I never witnessed the gifting of a shell again, but it did offer the opportunity to observe the martins’ group behavior at the shell trays. Sixteen smaller clam shells and sixteen larger clam shells were placed in separate trays under the gourd rack. |
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16 smaller clam shells in left tray |
The martins did not grab and fly.They often remained on the tray for several minutes, clutching a clam shell in their beak.
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These nine martins remained on the tray for several minutes after the shells were all gone. They kept looking at one another, perhaps expecting more shells to appear? | |
7/5/2018 Forty oyster shells on left |
7/5/2018 All clam shells were taken. 23 of 40 oyster shells remained at end of day. |
7/10/2018 - 9:46 am 30 oyster shells on left |
2 large clam, 7 small clam, 22 oyster left |
7/10/2018 - 6:21 pm. All clam shells taken. 19 oyster shells left. | This year's martin nests in the natural gourds were composed mostly of straw. |
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The purple martins used straw rather than pine needles even though abundant needles are always present under the large white pines and are offered at the gourd rack. Mud was mostly used in the plastic super gourds, perhaps to anchor the nest, preventing it from sliding around during construction. However, most natural gourds also have at least some mud. Fresh leaves were present in all nests. | |
For the first time starlings tried to nest in one of the gourds this year. The gourd was removed and there was no attempt to renest. | The martins are hesitant to land on the shell tray when I am near, so a car makes a quick and comfortable blind. Note the two small persimmon trees just left of the car. |
While observing the martins taking clam shells on 6/30/2018, one, then two and then three martins landed on the closer of two young persimmon trees and each began chewing off pieces of the base of a leaf. They methodically worked their way from edge to stem and appeared to have no interest in the rest of the leaf. It may be that they could only get a good perch on the leaf stem that would support their weight. This seemed to be a one time event. Persimmon leaves have antibacterial activity due to their tannins. Perhaps they also protect against parasites? Or, it may be just a case of “monkey see-monkey do” in selecting this small tree near their gourds. Once the threesome had finished, no further damage to either persimmon tree was noticed.
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While the martins exhibited a strong preference for smaller shells on June 30 and for larger shells on July 10, the variation in age of nestlings was substantial and I could not determine to which gourd each shell was taken or if the adult swallowed the shell. Even so, it is likely that younger nestlings were offered smaller shells.
barn owl | American kestrel | purple martin | barn swallow | Eastern bluebird |
tufted titmouse | Eastern phoebe | yellow shafted flicker | tree swallow | chimney swift |
house wren | big brown bat | Carolina wren | brown thrasher | catbird |
cedar waxwing | Northern mockingbird | |||
Yellow warbler | Acadian flycatcher |
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