Abstract
Simple SummaryIn 1981, the crested ibis (Nipponia nippon) was a critically endangered bird with only two pairs left in the world. Now, numbers have increased, and it has been reintroduced to many places in China, Japan, and Korea. In the breeding season, the crested ibis has high food needs (fish, freshwater invertebrate, etc.) to feed nestlings, and it prefers areas with rice paddies and waterbodies near to trees for nesting. We compared nest site preference from 1981 to 2019, and found that nest sites moved closer to houses of local farmers. In the 1980s, crested ibises only lived in remote mountain areas, where the farmers were too poor to afford pesticide and fertilizer, and consequently rice paddies contained substantial fish populations. In the meantime, the massive use of pesticides in more populated areas had caused the collapse of fish populations. A pesticide ban was enforced from 1981 on, when the crested ibis was rediscovered, and the freshwater biodiversity gradually recovered. The crested ibis returned to lower and more populated areas containing their ancestral habitats with large areas of wetlands.The number of breeding pairs of crested ibis (Nipponia nippon) in Hanzhong, China has recovered remarkably from 2 to 511 from 1981 to 2019. Although the crested ibis has been closely monitored, the habitat preference of the bird has not been well studied despite the extensive increase in abundance. We used nest site data from the past 39 years and 30 environmental variables to develop species distribution models for each year. We applied random forest to select important environmental variables, and used logistic regressions to quantify the changes in habitat preferences in 39 years, taking into account the effects of interaction and quadratic terms. We found that six variables had strong impacts on nest site selection. The interaction term of rice paddies and waterbodies, and the quadratic term of precipitation of the wettest quarter of the year were the most important correlates of nest presence. Human impact at nest sites changed from low to high as birds increased their use of ancestral habitats with abundant rice paddies. We concluded that during the population recovery, the crested ibises retained their dependence on wetlands, yet moved from remote areas to populated rural regions where food resources had recovered due to the ban of pesticide use.
Highlights
Species can be described as occupying ecological niches [1] and having certain preferences for environmental conditions [2,3,4]
The crested ibis has expanded to neighboring counties in Hanzhong Basin [20], which is surrounded by the Qinling Mountains to the north and Daba Mountains to the south
From 1981 to 2019, the crested ibis population increased from two breeding pairs to 511 breeding pairs (Figure 2), expanding from Yang County to other neighboring counties in Hanzhong Basin (Figure 1)
Summary
Species can be described as occupying ecological niches [1] and having certain preferences for environmental conditions [2,3,4]. Species distribution models can quantify such preferences, and rank the importance of different environmental variables [5,6]. The habitat preferences of a species could change over time due to exogenous anthropogenic pressures (e.g., human disturbance) or environmental variation, or endogenous factors such as intraspecific competition. The crested ibis (Nipponia nippon) has experienced a dramatic increase in numbers [7,8]. The habitat preferences of the crested ibis have been studied and key variables identified [8,9,10,11,12,13,14,15,16]. The population density of the ibis has greatly changed, no study has compared the changes in habitat preference of the species.
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