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.
Little owl
This owl becomes more vocal at night as the breeding season approaches in late spring. The nesting location varies with habitat, nests being found in holes in trees, in cliffs, quarries, walls, old buildings, river banks and rabbit burrows. A clutch of three to five eggs is laid (occasionally two to eight). The eggs are broadly elliptical, white and without gloss; they measure about . They are incubated by the female who sometimes starts sitting after the first egg is laid. While she is incubating the eggs, the male brings food for her. The eggs hatch after twenty-eight or twenty-nine days. At first the chicks are brooded by the female and the male brings in food which she distributes to them. Later, both parents are involved in hunting and feeding them. The young leave the nest at about seven weeks, and can fly a week or two later. Usually there is a single brood but when food is abundant, there may be two. The energy reserves that little owl chicks are able to build up when in the nest influences their post-fledgling survival, with birds in good physical condition having a much higher chance of survival than those in poor condition. When the young disperse, they seldom travel more than about . Pairs of birds often remain together all year round and the bond may last until one partner dies.