Answer: In my experience, butterflies do not seem to be deterred by scarecrows. Crows on the other hand can be very difficult to discourage. in particular, they seem attracted to new seedlings and baby transplants. Once the plants grow a little bit, the problem seems to decrease somewhat. In the meantime, however, to establish the plantings, you will need to do something.
Although a scarecrow is a typical image of bird deterring device, it doesn't usually work for very long. This means that whatever you use needs to be changed once the birds get used to it and are no longer afraid of it. This also means the birds will come to your birdbath once you remove the scarers -- and maybe while the scarers are in place, too! In addition to scarers, you can try physical barriers, these are not going to stop the birds from using the birdbath at all, but will protect the plants. Themost effefcive is setting a protective barrier of wire mesh over the plants/seed beds. Or possibly, a floating row cover would exclude them, although you would need to use the summer weight covering in warm weather.
You can also string clear monofilament fish line 6-8" above each row or planted area, and a couple down either side of the plot, to keep the birds from landing in the patch . They'll encounter the line when they try to land, and get confused by the unseen obstruction.
Continuous flagging is the most traditional way to keep birds/crows from crops such as corn. Stakes are placed 15 to 20 feet apart all around the corn patch and a long flag of cloth is attached to the top. The flag can be tied directly or tied first to a string and the string attached to the stake (gives more play iin the wind). Set up the stakes before the corn is attractive to the birds.
Another method, although more frequently used for ripening fruit trees or small fruits, is bird netting stretched above the ground.
Noise makers like a radio (got any neighbors who might be bothered?), aluminum pie pans on a scarecrow or line, metallic flash tape and mylar balloons (the reflection bothers the birds), have been used with varying degrees of success. Varying your scare tactics works best, as it keeps the birds from getting used to them.
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