Black-billed cuckoo
Many cuckoos are obligate brood parasites, meaning they only lay eggs in other birds' nests and never take care of their own young. Birds that do this, such as the common cuckoo or the brown-headed cowbird, lay relatively small eggs because their expected hosts are usually smaller birds. Cuckoos in the genus "Coccyzus", lay relatively large eggs even though they still parasitize smaller birds. Yellow warblers are the smallest birds recorded caring for black-billed cuckoo eggs. In experiments, these wood warblers were found to accept the cuckoo eggs 63% of the time even though their own eggs are only a quarter of the size. Even with the size difference, the warbler parent is often still able to raise the cuckoo as long as it can provide the chick with sufficient nutrition and incubation.
The black-billed cuckoo was originally placed in genus "Cuculus". This genus comprises Old World cuckoos that are all obligate brood parasites. Upon further genetic testing, it was placed into genus "Coccyzus" that comprises nine species of New World cuckoos. The black-billed and yellow-billed cuckoos are the only two that migrate into North America while the other seven are permanent residents of either Central or South America. Even though these two cuckoos overlap in range, they are not sister taxa. This suggests that the two species invaded North America separately. Although family Cuculidae is monophyletic, the genus "Coccyzus" was found to be polyphyletic.
Kori bustard
As with all bustards, the female makes no real nest. The female kori bustard lays her eggs on the ground in a shallow, unlined hollow, rather than the typical scrape. This nest is usually located within of a tree or shrub, termite mound or an outcrop of rocks. The hollow may measure in diameter and be almost completely covered by the female when she's incubating. Due to their ground location, nests are often cryptic and difficult for a human to find, unless stumbled onto by chance. The same site is sometimes reused in successive years. The kori bustard is a solitary nester and there is no evidence of territoriality amongst the females. Usually two eggs are laid, though seldom 1 or 3 may be laid. Clutch size is likely correlated to food supply. They are cryptically colored with the ground color being dark buff, brown or olive and well marked and blotched with shades of brown, grey and pale purple. Eggs are somewhat glossy or waxy and have a pitted-looking surface. Egg size is in height and width. The eggs weigh individually about , with a range of .