I believe the Declaration of Causes was written by a committee of the delegates to the Texas Secession Convention which convened at Austin Jan.28 1861-Feb.4 when it adjourned to await the popular vote. Feb.23 results 44,317 for --- 13,020 against.The convention was reassembled on March 5 and officially declared Texas Independent. The 2nd.session of the Convention was adjourned on March 23.

http://archive.org/stream/journalofsecessi00texarich/journalofsecessi00texarich_djvu.txt

Above should be the Journal of the Texas Secession Convention.

It is interesting a prominent Texan of German descent,Ferdinand Lindheimer of New Braunfels was employed by the State of Texas to print 5,000 copies of the Confederate Constitution(including various addresses of the Convention) and Carl Wilhelm Von Rosenberg was employed to translate the Constitution into German. I do not know but it is probable this may have included the Texas Declaration of Causes.