We will be doing the usual tourist things as a family, but I can't resist to see if there are any potential lifebirds in the area. Do you have any leads on: Yellow Rail, Mountain Plover, Sage Thrasher, Sprague's Pipit, Harris's sparrow, or any of the 3 Longspurs? If I thought the chances were decent I would try to workin an outing or two to try and grab one or more.
Thanks in advance for any thoughts which you can share.
My answer: All the birds can be found in winter in Texas, but in most cases you'd have to drive hundreds of miles to different parts of the state and have a lot of luck on your side.
Yellow rails are in the coastal marshes, but nigh to impossible to see unless you trudge through a cottonmouth invested marsh. They don't normally call during winter.
Mountain Plovers can show up anywhere, but most likely in farm fields around Austin and west of Rockport.
Sage Thrashers are possible in the Hill Country north of San Antonio in the Kerr Wildlife Management Area west of Kerrville.
Sprague's Pipits are a sure thing at the Atwater Prairie Chicken NWR near Sealy, TX.
Harris's Sparrows tend to show up in hedgerows along farm field roads between Houston and San Antonio; the farm roads of the Katy Prairie west of Houston is a good place to look.
Longspurs are reliably found in the Texas Panhandle north of Amarillo and especially around Dalhart in the grassy fields of ranches---but you have to do a lot of driving around those roads to spot them. In fact, of all the birds you listed, the longspurs are the surest thing if you have the time and patience to look. It can also be brutally cold and windy in the Panhandle during winter.