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The Home Habitat

Purple Martins’ use of clam shells in the 2018 nesting

Small 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.

clam shells for martins Purple martin taking larger clam shell

16 smaller clam shells in left tray
16 larger clam shells in right tray

The martins did not grab and fly.They often remained on the tray for several minutes, clutching a clam shell in their beak.
purple martin calcium purple martin calcium preference
6/30/2018 Picking the larger shells after the smaller shells were all taken
Purple martin taking clam shell Purple martin behavior
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?
40 oyster shells and 40 clam shells Clam shells taken first

7/5/2018 Forty oyster shells on left
40 clam shells on right

7/5/2018 All clam shells were taken. 23 of 40 oyster shells remained at end of day.
30 oyster and 30 clam shells large clam shells taken first

7/10/2018 - 9:46 am 30 oyster shells on left
15 smaller and 15 larger clam shells on right

4:16 pm - Large clam shells taken first
2 large clam, 7 small clam, 22 oyster left
clam shells taken first straw preferred over pine needles
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.

The purple martin’s strong preference for clam shells over crushed oyster shells is likely because the clam shell is easily recognizable and has served the martins well for millennia, allowing evolution to take its course. The crushed oyster shells are a recent product of the poultry industry and resemble gravel. One may be as beneficial as the other. But, the clam shells are more desirable to the martins. At one point, when the shells were almost gone, 5 martins, each clutching a large clam shell in its beak, just perched on the tray for several minutes and seemed to be staring at one another. Were they showing off their prized shell? Were they waiting for one of them to make a move? Suddenly all five flew off to the gourds. I did not see which one flew first, but their reaction time is much faster than mine.

purple martin nestlings purple martin eggs
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.
purple martin nest with 5 eggs
Removing a starling nest using a car as a blind
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.


persimmon leaves for purple martins

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.

2019-2020 Purple Martin nesting
2018 martins use of clam shells
2017 Purple Martin prey
Purple Martins 1997-2014

2022 update - Return of the barn owls
2021 Chimney Swift tower success!!!
2020 Barn Swallow nesting
Barn swallow nest cups
2019 Barn Swallows and Black Rat Snakes

2018 - The Barnyard Balance of Nature Goes Awry
Black rat snakes vs barn swallows, Northern flickers, kestrels and others

2018 Purple Martin preference for clam shells
2017 - Return of the Monarchs!
2017 Purple Martin prey photos
2010 - 2016 Northern flicker nestings
2014 house wren gourd use
2014 - A dramatic loss of many types of insects
2019-2020 Purple Martin nesting
2014 barn owl nesting - prey study
A new barn swallow shelter for 2013
2010 barn owl nesting
2010 Update
2016-2017 Kestrel nestings
Starling traps
Using blinds in the home habitat
Providing perches for birds
Providing snags for wildlife
The ugly young maple
2001 - 2013 nest cams
Use of tomato cages as hunting perches by insectivorous song birds
Vultures, beetles and the resurrection of life

Species of interest in our yard - photos and articles
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
Willow flycatcher
cedar waxwing Northern mockingbird
Blue-gray gnatcatcher
turkey vulture
Yellow warbler Acadian flycatcher

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