Parent–offspring conflict has explained a variety of ecological phenomena across animal taxa, but its role in mediating when songbirds fledge remains controversial. Specifically, ecologists have long debated the influence of songbird parents on the age of fledging: Do parents manipulate offspring into fledging to optimize their own fitness or do offspring choose when to leave? To provide greater insight into parent–offspring conflict over fledging age in songbirds, we compared nesting and postfledging survival rates across 18 species from eight studies in the continental United States. For 12 species (67%), we found that fledging transitions offspring from comparatively safe nesting environments to more dangerous postfledging ones, resulting in a postfledging bottleneck. This raises an important question: as past research shows that offspring would benefit—improve postfledging survival—by staying in the nest longer: Why then do they fledge so early? Our findings suggest that parents manipulate offspring into fledging early for their own benefit, but at the cost of survival for each individual offspring, reflecting parent–offspring conflict. Early fledging incurred, on average, a 13.6% postfledging survival cost for each individual offspring, but parents benefitted through a 14.0% increase in the likelihood of raising at least one offspring to independence. These parental benefits were uneven across species—driven by an interaction between nest mortality risk and brood size—and predicted the age of fledging among species. Collectively, our results suggest that parent–offspring conflict and associated parental benefits explain variation in fledging age among songbird species and why postfledging bottlenecks occur.

Host–symbiont relationships are ubiquitous in nature, yet evolutionary and ecological processes that shape these intricate associations are often poorly understood. All orders of birds engage in symbioses with feather mites, which are ectosymbiotic arthropods that spend their entire life on hosts. Due to their permanent obligatory association with hosts, limited dispersal and primarily vertical transmission, we hypothesized that the cospeciation between feather mites and hosts within one avian family (Parulidae) would be perfect (strict cospeciation). We assessed cophylogenetic patterns and tested for congruence between species in two confamiliar feather mite genera (Proctophyllodidae: Proctophyllodes, Amerodectes) found on 13 species of migratory warblers (and one other closely related migratory species) in the eastern United States. Based on COI sequence data, we found three Proctophyllodes lineages and six Amerodectes lineages. Distance‐ and event‐based cophylogenetic analyses suggested different cophylogenetic trajectories of the two mite genera, and although some associations were significant, there was little overall evidence supporting strict cospeciation. Host switching is likely responsible for incongruent phylogenies. In one case, we documented prairie warblers Setophaga discolor harboring two mite species of the same genus. Most interestingly, we found strong evidence that host ecology may influence the likelihood of host switching occurring. For example, we documented relatively distantly related ground‐nesting hosts (ovenbird Seiurus aurocapilla and Kentucky warbler Geothlypis formosa) sharing a single mite species, while other birds are shrub/canopy or cavity nesters. Overall, our results suggest that cospeciation is not the case for feather mites and parulid hosts at this fine phylogenetic scale, and raise the question if cospeciation applies for other symbiotic systems involving hosts that have complex life histories. We also provide preliminary evidence that incorporating host ecological traits into cophylogenetic analyses may be useful for understanding how symbiotic systems have evolved.

For most bird species, little is known about their ecology and survival between fledging and independence despite the potential for post-fledging survival to be a factor limiting population dynamics. Cerulean Warblers (Setophaga cerulea) are a declining migratory species, and full-life-cycle conservation efforts that include the post-fledging period are warranted to attempt to reverse their decline. To understand movement, habitat selection, and survival, we radio-tracked 20 fledglings throughout the dependent post-fledging period. Broods were split by their parents, typically (88%) left parental breeding territories within 12 days, and survivors moved 2.4 ± 0.7 km (mean ± SE) from their nest within the 28.1 ± 1.8 day tracking period. Fledglings were usually observed in the mid-canopy to upper canopy and selected habitat with greater mid-story cover, less basal area, and areas closer to water bodies, compared to available points, when considering data from the entire post-fledgling period. However, habitat selection varied with fledgling age. Young fledglings (0–2 days post-fledging) selected areas with greater sapling cover and less stand basal area, but as fledglings matured, they selected areas farther from canopy gaps with greater mid-story cover. Compared with nesting habitat selected by parents, fledglings used areas with smaller and more numerous trees, fewer canopy gaps, and greater mid-story cover. Survival of the entire period was 48 ± 14% and most (8/10) mortalities occurred within the first 3 days post-fledging. Evidence indicated eastern chipmunks (Tamias striatus) as the most common predator. Providing or retaining large tracts of forest is recommended to prevent the restriction of post-fledging dispersal, and managing forests to maintain a heterogeneous landscape that includes stands with numerous canopy gaps and dense understory (e.g., shelterwood harvests or late seral stage conditions) as well as stands with a dense mid-story (e.g., younger stands and riparian areas) appears to be important for this life stage.