Efficacy of autumn plowing as a management tactic for increasing the foraging energy efficiency of the Crested Ibis during the slack season

To clarify the effects of autumn plowing on the foraging energy efficiency of the Crested Ibis, Nipponia nippon, we determined the biodiversity and biomass in paddy fields, observed the ibis foraging behavior, and conducted a plowing manipulation experiment. From observations, the ibis foraging energy efficiency was calculated 20, 40, and 120 days after autumn plowing, and the ibis prey biomass and physical characteristics of the paddy fields used by the ibis were evaluated at the same times. Using this information, a statistical model explaining the ibis foraging energy efficiency was built using a generalized linear mixed model (GLMM). Path analysis was used to examine the cascade effect of autumn plowing on ibis foraging energy efficiency. In the plowing manipulation experiment, we set up three paddy treatments: no treatment as a control, rotary plow treatment, and subsoiler digger plow treatment. We then investigated the biomass, number of species, and ibis foraging energy efficiency before and after autumn plowing with each treatment.The GLMM showed that the ibis foraging energy efficiency was not determined by the prey biomass, but by the physical environment of the paddy field. Furthermore, path analysis revealed that autumn plowing increased the foraging energy efficiency until 20 days after plowing, while its positive effects were reduced drastically 40 and 120 days after plowing. In the plowing manipulation experiment, there was no significant difference in the number of species before and after plowing with any treatment. Both the rotary and subsoiler digger plows decreased the biomass in the paddy field, while increasing it in the paddy ridge. The GLMM indicated that the ibis foraging energy efficiency from before to after plowing decreased 0.6 times with no treatment, while it increased 1.7 times with the rotary plow treatment and 3.9 times with the subsoiler digger plow treatment.Our results suggest that autumn plowing temporarily increased the ibis foraging energy efficiency, but its effect did not persist for more than 40 days. Use of a subsoiler digger plow would be an effective tactic for increasing the ibis foraging efficiency without having a negative impact on paddy organisms.