The Yellow-headed Vulture is reported apparently for the first time from the peninsula. The specimens of the Streak-headed Woodhewer and the Louisiana Waterthrush are the second ones of each species taken on the peninsula. The Purple Martin taken on August 14, the Barn Swallow on August 18, and the Louisiana Waterthrush on August 14 represent earliest known autumn dates for these transients. Evidence for breeding is given for 20 species for the first time and extensions of the known breeding seasons are presented for 41 species. Fourteen genera, representing about 19 species, of Mallophaga are reported for 20 different species of bird hosts. At Pisté and Puerto Juarez, species of birds such as the Blue Honeycreeper and the Red-capped Manakin, normally thought of as characteristic of more humid areas, were found breeding in numbers near _cenotes_. However, they were not seen to venture far into the surrounding deciduous forest. The availability of suitable habitat brought on by the rainy season and the regular occurrence of _cenotes_ helps to explain the presence of such species far outside the Rain Forest zone. LITERATURE CITED BLAKE, E. R. 1953. Birds of Mexico a guide for field identification. Univ. of Chicago Press, Chicago, xxix + 644 pp. BRODKORB, P. 1943. Birds from the gulf lowlands of southern Mexico. Misc. Publ., Mus. Zool., Univ. Michigan., 55:1-88, January 30. FRIEDMANN, H., GRISCOM, L., and MOORE, R. T. 1950. Distributional check-list of the birds of Mexico Part I. Pac. Coast Avif., 29:1-202, June 30. JOHNSTON, R. F. 1962. The taxonomy of pigeons. Condor, 64:69-74, January 30. LOWERY, G. H., JR. and BERRETT, D. G. 1963. A new Carolina Wren (Aves: Troglodytidae) from southern Mexico. Occas. Papers Mus. Zool., Louisiana St. Univ., 24:1-3, December 20. MILLER, A. H., FRIEDMANN, H., GRISCOM, L., and MOORE, R. T. 1957. Distributional check-list of the birds of Mexico Part II. Pac. Coast Avif., 33:1-436, December 20. MONROE, B. L., JR. 1963. Notes on the avian genus _Arremonops_ with description of a new subspecies from Honduras. Occas. Papers Mus. Zool., Louisiana St. Univ., 28:1-12. PAYNTER, R. A., JR. 1955a. The ornithogeography of the Yucatán Peninsula. Bull. Peabody Mus. Nat. Hist., 9:1-347. 1955b. Additions to the ornithogeography of the Yucatán Peninsula. Postilla, no. 22, 4 pp. (unpaged). RIDGWAY, R. 1914. Birds of North and Middle America: a descriptive catalogue ... Bull. U.S. Nat. Mus., 50:xx+1-882, 35 pls., April 8. SELANDER, R. K. and GILLER, D. R. 1963. Species limits in the woodpecker genus _Centurus_ (Aves). Bull. Amer. Mus. of Nat. Hist., 124:215-273. SKUTCH, A. 1947. Life history of the turquoise-browed motmot. Auk, 64:201-217, April. STORER, R. W. 1961. Two collections of birds from Campeche, Mexico. Occas. Papers Mus. Zool., Univ. Michigan, 621:1-20, August 15. TRAYLOR, M. A., JR.