S. G.  E. Betts, ?Vertebrate contents of pellets cast by Barn-Owls (Tyto alba alba) in N.E. Worchestershire?, Ibis, vol. 598-600, 1936.

E. S.  Botelho and Arrowood, P. C., ?The effect of burrow site use on the reproductive success of a partially migratory population of Western Burrowing Owls (Speotyto cunicularia hypugaea)?, Journal of Raptor Research, vol. 32, pp. 233-240, 1998.

K.  Eisermann and Howell, S. N. G., ?Vocalizations of the Guatemalan Pygmy-Owl (Glaucidium cobanense).?, Journal of Raptor Research, vol. 45, pp. 304-314, 2011.