The first one looks a bit more like a hyoprora based on the rostral. The second one looks more like a microphthalmus. I'm not sure based on these pictures.
The best way to differentiate the two species is by looking at the subcaudal scales underneath the tail. In hyoprora, most of the subcaudals are not divided. In microphthalmus, the subcaudals are divided. Microphthalmus also has more ventral scales (137-173 vs. 124-141 in hyoprora). Hyoprora also tends to be found lower than 1000 meters ASL, while microphthalmus are usually found above 1000 meters ASL.
"The Venomous Reptiles of the Western Hemisphere" by Campbell and Lamar would be a great place to start. They have a lot of information on the genus, and probably have ecological data for the two species in question.
I also found some papers that might help you out:
Bernarde, P. S., FERREIRA-MARTINS, L. S., & Oliveira, J. R. (2008). Bothrocophias hyoprora (Amazonian hog-nosed pit viper). Diet. Herpetol. Rev, 39(3), 353.
(LINK-
http://www.herpetofauna.com.br/Bothroco ... oxDiet.pdf)
Bernarde, P. S., do Amaral, E. D. S., & do Vale, M. A. D. (2015). Squamata, Serpentes, Viperidae, Bothrocophias hyoprora (Amaral, 1935): Distribution extension in the state of Acre, northern Brazil. Check List, 7(6). (LINK-
http://www.checklist.org.br/getpdf?NGD115-11)
Cisneros-Heredia, D. F., Borja, M. A., Proano, D. A. N. I. E. L., & Touzet, J. (2006). Distribution and natural history of the Ecuadorian Toad-headed Pitvipers of the genus Bothrocophias. Herpetozoa, 19, 17-26. (LINK-
http://www.landesmuseum.at/pdf_frei_rem ... 7-0025.pdf)
DE CARVALHO, V. T., & DE FRAGA, R. A. F. A. E. L. (2013). Toad-headed Pitviper Bothrocophias hyoprora (Amaral, 1935)(Serpentes, Viperidae): New Records of Geographic Range in Brazil, Hemipenial Morphology, and Chromosomal Characterization. Herpetological Review, 44(3), 410-414. (LINK-
http://www.researchgate.net/profile/Ric ... e509f3.pdf)
GUTBERLET, JR, R. L., & Campbell, J. A. (2001). Generic recognition for a neglected lineage of South American pitvipers (Squamata: Viperidae: Crotalinae), with the description of a new species from the Colombian Chocó. American Museum Novitates, 1-16. (LINK-
http://digitallibrary.amnh.org/bitstrea ... sequence=1)
Valencia, J. H., Garzón, K., & BETANCOURTYEPEZ, R. (2008). Notes on the reproduction of the Ecuadorian Toad-Headed Pitviper Bothrocophias campbelli (FREIRE-LASCANO, 1991). Herpetozoa, Wien, 21(1/2), 95-96. (LINK-
http://www.landesmuseum.at/pdf_frei_rem ... 5-0096.pdf)
Voss, R. S. (2013). Opossums (Mammalia: Didelphidae) in the diets of Neotropical pitvipers (Serpentes: Crotalinae): Evidence for alternative coevolutionary outcomes?. Toxicon, 66, 1-6.
Good luck with your study
-Justin