As per the new law. Roads and ROW's are off limits to anything that involves picking up, capturing or even moving snakes. Taking one overnight just to photo could end someone up with a ticket or even jail time (class B misd.) Private land is OK as long as you have a license. Here are the relevant quotations from the Texas Parks and Wildlife Code:
§ 1.101. DEFINITIONS. In this code:
(1) "Hunt" means capture, trap, take, or kill, or an
attempt to capture, trap, take, or kill.
(2) "Catch" means take or kill and includes an attempt
to take or kill.
(3) "Sell" means to transfer the ownership or the
right of possession of an item to a person for consideration and
includes a barter and an even exchange.
(4) "Wild," when used in reference to an animal, means
a species, including each individual of a species, that normally
lives in a state of nature and is not ordinarily domesticated. This
definition does not include exotic livestock defined by Section
161.001(a)(4), Agriculture Code.
(5) "Take," except as otherwise provided by this
code, means collect, hook, hunt, net, shoot, or snare, by any
means or device, and includes an attempt to take or to pursue in
order to take.
Link:
http://tlo2.tlc.state.tx.us/statutes/docs/PW/content/htm/pw.001.00.000001.00.htm#1.101.00
AND THE LAW WE'RE TRYING TO GET CHANGED:
§ 62.0031. HUNTING FROM PUBLIC ROAD OR RIGHT-OF-WAY
PROHIBITED. (a) Except as provided by Subsection (b), a person
may not hunt a wild animal or bird when the person is on a public
road or right-of-way.
(b) This section does not apply to the trapping of a raptor
for educational or sporting purposes as provided by Chapter 49.
Link:
http://tlo2.tlc.state.tx.us/statutes/docs/PW/content/htm/pw.005.00.000062.00.htm#62.0031.00
So I guess you could always tell them you're looking for Eagles for Sporting purposes 
HCU has several ranches on their landowner agreement program. By joining you will have access to them all. Many are in the areas that you plan on going.
Either way, have fun...
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HCU
Snakes of Hudspeth County, Texas