设\(P\)为双曲线\( \dfrac {x^{2}}{a^{2}} -y ^{2} =1(a > 0)\)上的一点，\(F _{1}\)、\(F _{2}\)分别是双曲线的左、右焦点，\(∠F _{1} PF _{2} = \dfrac {2π}{3}\)，则\(\triangle F _{1} PF _{2}\)的面积等于\((\:\:\:\:)\)
A. \( \sqrt {3} a ^{2}\)
B. \( \dfrac { \sqrt {3}}{3} a ^{2}\) C. \( \dfrac { \sqrt {3}}{3}\) D. \( \dfrac {2 \sqrt {3}}{3}\)
