Header loses uper case in rmarkdown + tufte

Question

I'm trying to keep the uppercase part of the title in the page-headers; it shows ok in the title page, so I'm looking for a way to pass text as it is from the yaml header to the page headers, I've seen examples with plain latex where passing strings as they are is the default behavior, so I guess it is somewhere in the chain yaml-rmarkdown-tufte; my yaml header is the following, it renders "guatemala", so I'd like to have the capital G here.

link to log file

---
title: "Intercambio de experiencias en restauración de manglar: Guatemala"
output:
  tufte::tufte_handout:
    citation_package: natbib
    latex_engine: xelatex
  tufte::tufte_html: 
    self_contained: yes
  tufte::tufte_book:
    citation_package: natbib
    latex_engine: xelatex
author: "Pronatura Veracruz"
date: "`r format(Sys.time(), '%d %B %Y')`"
link-citations: yes
bibliography: biblio.bib
lang: es
urlcolor: blue
linkcolor: blue
header-includes:
  - \usepackage{titling}
  - \pretitle{\begin{center}
    \includegraphics[width=2in,height=2in]{lancha.jpg}\LARGE\\}
  - \posttitle{\end{center}}
  - \usepackage{tocloft}
---