Calcium is Not a Limiting Micronutrient for Egg Production by Green-Backed Tits in a Mosaic Landscape of Mixed-Oak Forest and Cedar Plantation in Subtropical Taiwan

Abstract In many passerines, reproductively active females must forage for calcium-rich materials on a daily basis to meet exact calcium demands during egg production. Calcium availability often constrains reproductive output in birds, but is dependent on species-specific foraging traits and local calcium availability, and, thus, land use. Here, we examined whether calcium availability limits the reproductive output of Green-backed Tits Parus monticolus over a four-year period in mid-altitude subtropical forest of Taiwan. We compared soil nutrients and the availability of calcium-rich snails between mixed-oak forest and Japanese cedar Cryptomeria japonica plantation. We also provided supplementary calcium (in the form of snail shells and chicken egg-shells) in the nest boxes of half of all pre-laying pairs breeding in both habitats. The reproductive output of birds across the two treatments and two habitats was recorded. Our results showed that the soil was very acidic in both habitats. Compared to the mi...