Geographic variability in acoustic signals has been documented in many bird species. However, geographic variations in alarm calls have been so far neglected despite their crucial role on reducing risk to group members and relatives. We analyzed the note types and acoustic parameters of Japanese tit (Parus minor) alarm calls to three types of intruders (a nest predator, an adult predator, and a harmless species) from three populations in China. Our results revealed that tits in the same population produce similar note types to different intruders, but the three populations only shared six note types and each population had unique note types. The frequency and duration parameters of three shared common note types were significantly different among populations. The three populations belong to the same species, thus they have shared note types. We suspect that the unique note types occurring in each population may be related to three potential reasons: founder effect, predation pressure, and vocal learning. The differences in acoustic parameters of common notes among populations may be a consequence of adaptations to their environments. We suggest that population differences in the note levels of bird alarm calls do exist.

Niche theory predicts that ecologically similar sympatric species should show differentiation in at least one of the main niche dimensions (time, space, and/or food). Here, we combined observations of breeding timing, nest site selection, and diet (the latter determined using DNA metabarcoding) to analyze the niche overlap and differentiation between two sympatric secondary cavity‐nesting birds, the Japanese Tit Parus minor and the Yellow‐rumped Flycatcher Ficedula zanthopygia. The results showed that (1) there were significant differences in the first egg laying date, length of the egg laying period, incubation date, and hatching date between tits and flycatchers, and the breeding time of flycatchers peaked later (about 30 days) than that of tits; (2) the two species had a large overlap in nest site selection, although the canopy coverage and shrub density of flycatchers were significantly higher than those of tits; and (3) the niche overlap in diet was minimal, with both species heavily relying on Lepidoptera (39.6% and 63.7% for tits and flycatchers, respectively), but with flycatchers consuming significantly higher percentages of Lepidoptera, Diptera, and Coleoptera than tits. The results indicate that these two sympatric secondary cavity‐nesting species have significant niche differentiation in breeding time and diet, but little differentiation in nest site selection.

The gut microbiota forms early in life and undergoes dynamic changes that are essential for host health and development. Although body condition is a key fitness-related trait and predictor of viability in many animal species, its association with gut microbiota, especially during early life stages in wild populations, remains poorly understood. In this study, we collected fecal samples and used 16S rRNA gene sequencing to investigate temporal shifts in gut microbiota of Japanese tits (Parus minor) across nestling stages (days 3, 6, 10, and 14 post-hatching, denoted as D3, D6, D10, and D14, respectively; n = 70, repeatedly sampled) and in adults (n = 25), and examined their association with nestling body condition. The results showed that nestlings harbored distinct microbial communities compared to adults, with the latter exhibiting higher relative abundances of Bacteroidota and Verrucomicrobiota (LMMs, p < 0.001 for both). LEfSe analysis identified Actinobacteriota as a biomarker for D14 nestlings and Bacteroidota for adults. Alpha diversity decreased from D3 to D14, with adults showing higher diversity than late-stage nestlings (D10–D14), but comparable diversity to early-stage nestlings (D3–D6). Beta diversity revealed clear separation between nestlings and adults, and within nestlings, early stages (D3–D6) differed significantly from D14. Nest effects also contributed to microbial structure. Time-lagged analyses showed that Firmicutes abundance at D6 positively predicted scaled mass index (SMI) at D10 (p = 0.002), whereas Proteobacteria negatively predicted SMI (p = 0.006). Overall, these findings highlight dynamic, stage-specific shifts in the gut microbiota of Japanese tits and suggest that microbial succession may influence nestling growth and physiological adaptation.