Prof. Aldo Leopold                                          . 
1532 University Ave. 
Madison, Wisconsin 
Dear Aldo:                                              IV 
I am having sent under separate cover a raptor tether made of a 
section of one of the side chains of an old tire chain, wire, a 
commercial swivel, and an anklet made of a piece of a worn out 
In making this show up to the best advantage on your slide, I 
would suggest that you actually fasten the tether to the tarso- 
metatarsus of a horned owl museum specimen and photograph on the 
leg of the bird. You may keep the tether for demonstration 
purposes, also, if you wish. 
This tether has been used on marsh hawks, but I have adjusted the 
loop to accommodate horned owls, as well. I think it would be best 
to use the horned owl as an example and to encourage tethering of 
horned owls for a number of reasons, among which the chief are (1) 
less likelihood of the tethered birds injuring themselves, (2) 
greater scientific need of continued work with horned owls in 
connection with population studies (the horned owl being about the 
best indicator of general vulnerability of prey), (3) longer period 
over which studies of tethered birds may profitably be carried on 
with a minimum of actual visits. 
The tether may still be adjusted to marsh hawks, however, and I 
have deepened the notches to show you where the leather should 
be matched up. I have only partly wired the anklet, just enough 
to show how it is done. The small openings in the anklet between 
notches are very important, and one strand of wire should be run 
through the proper ones the first thin' before wiring the anklet 
completely and tightly. This, of course, is to prevent slipping 
in case the leather becomes wet or pulled out of shape. The 
leather anklet on the sample is not of ideal shape but it is the 
only one I have cut at present; the anklet where it comes in 
contact wit'- the raptor's leg should be wide, soft, strong, and 
loose-fitting enough not to chafe excessively or to shut off