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.
Black robin
Eggs are laid between early October and late December. A second clutch may be laid if the first is unsuccessful. The clutch size varies from one to three eggs, but two is typical. Eggs are creamy in colour with purple splotches. When the eggs are laid the female will sit on them to keep them warm until they hatch in about 18 days. Then both parents will help to feed the chicks. Chicks often spend the first day or two, after leaving the nest, on the ground - a dangerous place to be for it with predators that are possibly there. Young robins stay in the nest for about 23 days after hatching, but even after leaving the nest the parents will continue to feed them until they are about 65 days old. This period of parental care is longer than would normally be expected for a bird of its size.