biennial migration
In sharks (Naidoo et al. 2017):
C. taurus females undertake a biennial migration along the east coast of SA of approximately 1000 km from their gestation grounds to their pupping grounds in the south, so they are not exposed to any single point source of pollution such as a marine outfall or an industrialised harbour for lengthy periods.
biennial life cycles
Semivoltine, biennial are good search terms for answering this question, e.g.: https://scholar.google.com/scholar?q=semivoltine+biennial
As other answers have suggested, most of the examples we find this way are insects living in relatively cold environments where it may take more than one year to complete a life cycle (I haven't come across any examples where the life cycle is always biennial — generally these species have univoltine (one generation per year) or faster life cycles in warmer climates and semivoltine/biennial cycles in colder climates.
e.g. Sota 1996:
Two closely related Leptocarabus [beetle] species overwintered as larvae in the first winter and as adults in the second and later years; one species occurred at altitudes from 750 to 2200 m, and its life cycle changed from annual to biennial in the subalpine zone. The other smaller species occurred from subalpine to alpine zones and had a biennial life cycle.
evolutionary argument
This is somewhat hand-wavy, but it appears that most examples of biennial life cycles/migration occur in organisms with sufficiently rates of growth (in the case of insects) or resource acquisition (in the case of sharks) that they cannot manage to complete their life cycle or reproduce in a single year, so must delay until a second year. (These organisms also live in environments that are sufficiently seasonal that they must synchronize with the annual cycle in some way.)
Naidoo, Kristina, Anil Chuturgoon, Geremy Cliff, Sanil Singh, Megan Ellis, Nicholas Otway, Andre Vosloo, and Michael Gregory. “Possible Maternal Offloading of Metals in the Plasma, Uterine and Capsule Fluid of Pregnant Ragged-Tooth Sharks (Carcharias taurus) on the East Coast of South Africa.” Environmental Science and Pollution Research 24, no. 20 (July 1, 2017): 16798–805. https://doi.org/10.1007/s11356-017-9281-1.
Sota, Teiji. “Altitudinal Variation in Life Cycles of Carabid Beetles: Life-Cycle Strategy and Colonization in Alpine Zones.” Arctic and Alpine Research 28, no. 4 (November 1, 1996): 441–47. https://doi.org/10.1080/00040851.1996.12003197.
