Check these sites before you come and during your stay. They will have the most up to date info, especially on rarities that show up:
Texbirds:
http://birdingonthe.net/mailinglists/TEXS.html
NARBA:
http://www.narba.org/(X(1)S(t2y5dy55pbflrqjtjkasdnut))/Default.aspx?AspxAutoDetectCookieSupport=1. On the NARBA site, scroll down and click on the Texas Rare Bird Alert.
If you are going to be along the coast in the Corpus Christi area I recommend:
Port Aransas - go to Paradise Pond, check the beaches, the Leona Turnbelle Birding Center and a spot called Charlies Pasture which is actually behind the birding center, but you have to take some back roads to get to it. It has a very nice long boardwalk and often good things are found there. I will look up the directions & post them for you.
In Corpus Christi, you can try Blucher Park - an absolute favorite of mine in the spring; Tule Lake (which was a bit of trouble to actually find & has only a bit of a parking spot if you want to call it that!); there is a cemetary whose name I can't recall, but will post later; Polly Wog Ponds - can be good, but aren't well marked; Hans A. Suter Nature Park is a great spot for shorebirds, as well as passerines; there are other spots but I am not recalling them at the moment. Will post later. Also Hazel bazemore Park in CalAllen, just outside of Corpus Christi.
Feb is a bit tough on the upper & mid coast because spring migration hasnt usually begun yet...but here in Texas anything can happen! The valley is about 2 hrs south west of the middle Texas coast. If you have time to head to the valley - Sabal Palms Sanctuary is open again and it is a very pretty place, Santa Anna NWR. Estero Llano State Park, McAllen Cemetary, Bentsen-Rio Grande State Park, Edinburg Wetlands, Laguna Atascosa, Valley nature Centure, Frontera Audubon, Sarita rest stop and more.
Here are the names of some books that helped me when I went down to those areas:
http://www.amazon.com/Birding-Corpu...=sr_1_1?ie=UTF8&s=books&qid=1295229113&sr=1-1
http://www.amazon.com/Birding-Texas...=sr_1_2?ie=UTF8&s=books&qid=1295229113&sr=1-2
http://www.amazon.com/Exploring-Gre...=sr_1_3?ie=UTF8&s=books&qid=1295229113&sr=1-3
http://www.amazon.com/Finding-Birds...=sr_1_4?ie=UTF8&s=books&qid=1295229113&sr=1-4
These maps are great and worth the little bit they charge for them:
http://beta-www.tpwd.state.tx.us/huntwild/wildlife/wildlife-trails/coastal/