On July 1, 1912, after 100 years as a state, Louisiana's legislature adopted an official state flag. The pelican became the central image on the flag because it was the central image on the state seal. In Louisiana's second year as a state, in 1813, the legislature passed an act stating that Louisiana was to have an official state seal and that the governor was authorized to determine what that seal would be.
Gov. Wm C. C. Claiborne was familiar with the mythology of the mother pelican tearing flesh from her breast to feed her young. The image, representing self sacrifice, was common in Catholic and Masonic art. Louisiana's citizens were mostly Catholic and Claiborne was a Mason. That, plus the fact that the pelican was common to LA coasts possibly contributed to his choice of the iconic symbol of sacrifice as the central image in the state seal. (Sadly, pelican mothers will not tear at their own flesh to feed their young, but the legend may have stemmed from a misunderstanding of normal feeding behavior in which the parent holds its bill down against its breast to enable the nestlings to reach in to feed from the parent's pouch.)
While LA was still a territory and Claiborne was the territorial governor, the official seal was Claiborne's personal seal which featured an eagle. Sometime before the legislature called for an official state seal, Claiborne had begun using a seal featuring the pelican.
The first seal had 10 chicks in the nest. The seal also included scales of justice, 18 stars and the phrase "Justice, Union & Confidence." Over the years, the arrangement of pelicans, stars, scales and motto changed. Soon after the adoption of the seal, flags started to appear with the state seal on them. Both the flags and the seals varied over the years.
In 1902, Gov. Wm. Henry Wright Heard formalized the state seal with this description: "A pelican, with its head turned to the left, in a nest with three young; the pelican, following the tradition, in act of tearing its breast to feed its young; around the edge of the seal to be inscribed, "State of Louisiana.' Over the head of the pelican to be inscribed 'Union, Justice," & under the nest of the pelican to be inscribed 'Confidence.'"
At this time, a flag with a blue field and the seal as described came into common use, but there was no legislative authority for this flag. That was remedied in 1912 with these words: "That the official flag of Louisiana shall be that flag now in general use, consisting of a solid blue field with the Coat of Arms of the State, the pelican feeding its young, in white in the center, with a ribbon beneath, also in white, containing in blue the motto of the State, 'Union, Justice and Confidence,' the whole showing as below."