Do Owls Attack Purple Martin Decoys?

Reprinted from: Update 11(1)
Thomas B. Dellinger
PO Box 380163

George P. Dellinger
4108 Liberty Woods Ct.
Hartsburg, MO
65039, TX

Robert L. Dellinger
2767 US 231 S
Crawfordsville, IN
[email protected]

The three of us are brothers and have a long-shared heritage of dealing with Purple Martins all the way from the rough-wood martin houses on our family's 1930's Indiana farm to our present three colonies that we talk about nearly every time we call, write, or meet.

Today's martin conversation piece is about owl predation on George Dellinger's colony in central Missouri.

Brother Bob, with a martin colony in central Indiana, has carved wooden decoy martins and supplied them to all his kith and kin that have martin colonies. Bob's decoys figure prominently in this story.

Brother George had placed Bob's wooden decoys on his martin house much as shown in Fig. 1. Four decoys were near the ends of two 1/2" dowel rods placed across the roof gutters of a Trio Grandpa. The dowels were bolted to the roof with small bolts placed about 4" from the end edge of the roof. The decoys were clamped near the ends of the rods.

In 1997 George's colony was progressing nicely with three compartments containing 10 young from 8 to 14 days-of-age. Then, on the next nest check, there were no young at all and one of the decoys was missing.

The following day, while George was mowing his yard, he found the decoy in the grass about 70 yards away from the martin house. The next day another decoy was found about 50 yards away. In both cases the dowel rod had been broken at the bolt hole nearest to the decoy. An analysis of the location of the bolt on the roof would suggest that the rod was broken by an upward pull.

What was the answer to this mystery? There had been no wind strong enough to break off the decoys and carry them away. There was no other damage to the house. George had seen an occasional Great Horned Owl (Bubo virginianus) in the area. George did not find any remains of young martins on the ground.

The analysis and speculation is that the young martins were all robbed and taken by a Great Horned Owl in the period from one inspection to the next, and that the young were carried off and away from the house.

We also speculate that the owl hit the wooden decoys and that the breaking of the dowel would have been by a lifting motion. The owl would have carried the broken pieces of the dowel rods and the wooden decoys the distance of 50 to 70 yards before dropping them. Can you imagine the owl expecting a tasty morsel of soft martin, but ending up with a hard wooden piece and a trailing length of wooden rod?

The moral of this story is that the martin houses need protection from owl predation. You can bet that the next year there was an owl guard on George's house.

[Editorial comment: The PMCA has also received several reports of hawks attacking martin decoys, sometimes even leaving talon marks behind in the material. Besides helping novices attract their first martins, decoys may actually help reduce martin predation by drawing the attacks of raptors away from genuine martins.]

All three Dellinger brothers were raised on a small farm near Crawfordsville, Indiana. All three are now retired and each has a martin colony. Tom was an engineer and is now a frequent contributor to this magazine. George was a 36-year wildlife biologist with the Missouri Department of Conservation. Bob, who remained in Crawfordsville, was a farmer who turned his career to factory work.

Copyright 1998 by Purple Martin Conservation Association. All Rights Reserved.

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