Monitoring Tips:
Preventing Premature Fledging

Includes instructions for making the TG-12 quieter

Reprinted from: Purple Martin Update 6(3): 8

Dr. Thomas B. Dellinger
Box 380163
Duncanville, TX 75138-0163

"Jumpy" nestlings can be kept in their compartments during nest checks using the string and sock technique described in this article.

Nest monitoring is an important part of being a successful martin landlord. Since nesting activities take place over an extended time period, due to the spread-out arrival time of adult and subadult martins, a typical housing system will contain young of all ages. When the same housing system contains both older (20+ days) and younger nestlings, special care is sometimes required when monitoring nests, to avoid causing premature fledging of older nestlings.

In many years of working with Purple Martins, I have found that martin young over about 20 days of age will sometimes leave the houses prematurely after they are disturbed by a nest check. Young birds leaving the house at this age are at risk of not surviving. Many will end up on the ground, unable to fly; these are usually caught and put back in the house. Even so, these same birds may jump again before the house is back up in position and the birds have quieted down.

Young martins between 22-27 days old are also at risk of not surviving, even if they fly and stay in the air until well away from the house. Young that fledge normally will have a parent accompanying and helping them. Even though they are old enough to fly well, young that fledge without this parental care may not survive. Thus, it is important that young birds not jump too early. During nest checks, every effort should be made to keep the young in the house, and quieted down, so that they do not fledge prematurely, or without their parents' attention.

I have found that rag plugs inserted in the openings will keep young birds in the houses as I monitor the nests or band the young. I always lower the houses gently. Then, before I do any monitoring, I look into each compartment to see if there are any young old enough to pose a risk of fledging prematurely [looking at Project Martinwatch records will also work]. If I see young that are possibly old enough to jump, I put a rag plug in the opening to keep the birds inside. I leave these rag plugs in the openings as I monitor all the nest compartments.

Each rag plug has a 15-foot string attached to it so I can pull it out from the ground, once the house is back up in position. After the house is raised, I leave all the plugs in place for 5 minutes before removing them. In this way, the young will calm down and be more likely to remain in the house.

Further, on Trio Grandpas, the construction is such that a loud rasping noise usually occurs when the houses are raised or lowered with the lanyard. This noise is due to the "tin box" effect of a thin metal shell and the edges of two metal base plates being dragged across the pole. The resulting noises and vibrations are sometimes loud and disturbing enough that older nestlings will occasionally become frightened and leave the house prematurely.

To prevent this noise/vibration, I have removed the two centering plates that rub on the pole, ground their metal openings to a larger diameter, then inserted a section of 3/8" plywood, fitted onto the two plates. The metal centering plates remain, but the contact points are now wooden, so the rasping noise and vibration are essentially eliminated. My houses now go up and down quietly.

To retrofit a TG-12, the metal plates are removed, and their openings enlarged with an electric drill motor and a small grinder stone. Drill an opening for the pole in the plywood. Center the wooden opening so that the plate metal does not contact the metal pole. Use the plate as a template, and drill bolt holes in the plywood. Use bolts that are 3/8" longer than what originally came with the house.

The noise is exacerbated even more with a safety catch that is placed on some of the houses. Even though the safety catch is a good idea for stopping dropped houses from falling on human heads, the noise the catch creates is not to my liking, and I have removed the safety catches from all of my houses.

By following the techniques and modifications outlined above, I am able to monitor all nests, and band the young, without causing nestlings to fledge prematurely.


PMCA staff member, Ken Kostka, inserts a cup and string into each gourd that contains nestlings 24 days of age or older during a late season nest check. This technique helps prevent premature fledging of older nestlings. In combination with the Prognosticator, the baby pictures, and Project Martinwatch nest record sheets, a landlord should know the exact age of every nestling BEFORE they lower their housing for a check. Cavities with nestlings in the 24+ day age bracket are plugged as soon as housing is lowered, then are checked. The cup is removed, using the string, after the house is raised back up.

Copyright 1995 by Purple Martin Conservation Association. All Rights Reserved.

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