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.
Indigo bunting
These birds are generally monogamous but not always faithful to their partner. In the western part of their range, they often hybridize with the lazuli bunting. Nesting sites are located in dense shrub or a low tree, generally above the ground, but rarely up to . The nest itself is constructed of leaves, coarse grasses, stems, and strips of bark, lined with soft grass or deer hair and is bound with spider web. It is constructed by the female, who cares for the eggs alone. The clutch consists of one to four eggs, but usually contains three to four. The eggs are white and usually unmarked, though some may be marked with brownish spots, averaging in size. The eggs are incubated for 12 to 13 days and the chicks are altricial at hatching. Chicks fledge 10 to 12 days after hatching. Most pairs raise two broods per year, and the male may feed newly fledged young while the females incubate the next clutch of eggs.