Yellow Warbler - Breeding

Breeding

As usual for New World warblers (Parulidae), they nest in trees, building a small but very sturdy cup nest. Females and males share the reproductive work about equally, but emphasize different tasks: females are more involved with building and maintaining the nest, and incubating and brooding the offspring. Most of the actual feeding is also done by them. Males are more involved in guarding the nest site and procuring food, bringing it to the nest and passing it to the waiting mother. As the young approach fledging, the male's workload becomes proportionally higher.

The Yellow and Mangrove (including Golden) Warblers differ in some other reproductive parameters. While the former is somewhat more of an r-strategist, the actual differences are complex and adapted to different environmental conditions. The Yellow Warbler starts breeding in May/June, while the Mangrove Warbler can be found breeding all year round. Yellow Warblers have been known to raise a brood of young in as little as 45 days, but usually take about 75 days. The tropical populations, by contrast, need more than 100 days per breeding. Males court the females with songs; a Yellow Warbler has been observed to sing more than 3,200 songs in one day. They are, like most songbirds, generally serially monogamous; some 10% of Mangrove Warbler and about half as many Yellow Warbler males are bigamous. Very few if any Yellow Warblers breed more than once per year; around one in twenty Mangrove Warbler females will do so however. If a breeding attempt fails, either will usually try and raise a second brood successfully though.

The clutch of the Yellow Warbler is 3–6 (typically 4–5, rarely 1–2) eggs. Incubation to hatching usually takes 11 days, but may take up to two weeks. The nestlings weigh 1.3 g (0.046 oz) on average, and are brooded for an average 8–9 days after hatching, and leave the nest the following day or the one thereafter. Mangrove Warblers, on the other hand, have only 3 eggs per clutch on average and incubate some 2 days longer. Its average post-hatching brooding time is 11 days. Almost half of the parents (somewhat more in the Mangrove Warbler, somewhat less in the Yellow Warbler) attend the fledglings for some time after these leave the nest. This post-fledging care can extend for two additional weeks or more, and sometimes the pairs separate early, each accompanied by one to three of the young.

Some 3–4 weeks after hatching, the young are fully independent of their parents. They become sexually mature at one year of age, and attempt to breed right away. Only about one in four Mangrove Warbler nests successfully fledge any offspring, due to accidents and predation frequently causing total loss of the clutch. By contrast, 55% of all Yellow Warbler nestings are successful in raising at least one young.