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Ornithological Science
Abstract
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 mixed-oak forest, the litter in the cedar plantation contained marginally significantly more calcium, while the soil had significantly higher pH and exchangeable Ca2+. The cedar plantation supported similar, or even higher, snail abundance than the mixed-oak forest. We found no abnormal eggs with defective shells in either habitat. We also found no significant difference in clutch size, egg mass, egg shape index, egg volume, clutch volume, or hatching success across the two calcium-treatment groups or the two habitats. Calcium availability had a weak effect on the reproductive output of birds in the two habitats, possibly because the study area supported a high abundance of snails. Our results, combined with our calculations of the calcium demand of birds, suggest that calcium is not a limiting micronutrient for egg production by Green-backed Tits in the montane forest of subtropical Taiwan at present.
We thank Hsin-Te Yang, Kung-Kuo Chiang, Mu-Chun Yao, Po-Yin Chen, Shu-Yen Huang, Shih-Han Hsu, Yu-Chieh Pan, Chia-Chun Tsai, and the members of the Wildlife Laboratory of the Department of Life Science, National Taiwan Normal University, for assisting during fieldwork and providing valuable comments. We also thank Dr. Chiang-Her Yen and the members of the Forest Soil and Tree Mycorrhiza Laboratory, Department of Forestry, National Chung Hsing University for assisting with the soil survey and analysis. We thank Dr. Jim Reynolds and the anonymous reviewer for providing valuable comments on a draft of our manuscript. Our research was partly supported by the Shei-Pa National Park Headquarters with a grant to M.-T. Shiao. The funder did not have input on the content of the manuscript, nor did the funder require approval of the manuscript before submission or publication. The bird banding permits were issued by Shei-Pa National Park Headquarters and Miaoli County Government. The bird rings were provided by the Taiwan Bird Banding Center of the Wild Bird Federation Taiwan. There are no conflicts of interest to declare.
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