\documentclass{beamer}
\usepackage{tikz}
\usetikzlibrary{positioning,automata,overlay-beamer-styles}
\tikzset{orange on/.style={alt=<#1>{orange}{}}}
\begin{document}
\begin{frame}
\frametitle{Ducks}
\begin{tikzpicture}[shorten >=1pt,node distance=2cm,on grid,auto]
\node[state,initial] (s) {$s$};
\node[state,accepting] (g_1) [above right=of s] {$g_1$};
\node[state,accepting] (g_2) [below right=of s] {$g_2$};
\path[->]
(s) edge[orange on=1] node {b} (g_1)
edge[orange on=2] node [swap] {a} (g_2)
edge[orange on=3] [loop above] node {a,b} ()