Leporids have long been known to reingest soft faeces. However, it was recently found that they regularly reingest hard faeces, too. During the daytime, both soft and hard faeces are defecated and all of the faeces are reingested. Excreted at night are the hard faeces, which are normally discarded but reingested in starvation. The separation mechanism in the proximal colon, which diverts fine particles into the caecum and thus only passes large food particles, produces hard faeces. When the mechanism ceases acting, fermented caecal materials are excreted as soft faeces. The reingestion of soft faeces, rich in vitamins and microbial proteins, is physiologically imperative. Hard faeces are basically a refuse, but their thorough mastication at reingestion reduces poorly digestible large particles to fine ones good for fermentation. The regular reingestion of daytime hard faeces thus promotes food digestibility. The temporary use of night-time hard faeces allows leporids to do without food for some time. It thus gives leporids behavioural flexibility and thereby an ecological advantage. Reingestion is also known in other small-to medium-sized herbivores, which are all caecal fermenters. Morphological differentiation between faeces is reported only in larger species, but all ingested faeces are found to be richer in nutrients than discarded ones. Thus a separation mechanism is probably present in all reingesting species. Reingestion activity is deeply related to other behavioural and physiological traits of small mammalian herbivores, hence its study is important to understanding of their ecology and biology. Leporids are the largest of the reingesting species except for the semi-aquatic Coypu, and reingestion by leporids is certainly the most sophisticated. This development of a reingestion-involved digestive system has probably brought them to their present niche, as terrestrial medium-sized generalist mammalian herbivores, and consequently made their characteristic hide-and-run lifeforms by exposing them to a strong predation pressure.

We have estimated the number of sika deer, Cervus nippon, in Hokkaido, Japan, with the aim of developing a management program that will reduce the level of agricultural damage caused by these deer. A population index that is defined by the population divided by the population of 1993 is first estimated from the data obtained during a spotlight survey. A generalized linear mixed model (GLMM) with corner point constraints is used in this estimation. We then estimate the population from the index by evaluating the response of index to the known amount of harvest, including hunting. A stage‐structured model is used in this harvest‐based estimation. It is well‐known that estimates of indices suffer from large observation errors when the probability of the observation fluctuates widely; therefore, we apply state‐space modeling to the harvest‐based estimation to remove the observation errors. We propose the use of Bayesian estimation with uniform prior‐distributions as an approximation of the maximum likelihood estimation, without permitting an arbitrary assumption that the parameters fluctuate following prior‐distributions. We are able to demonstrate that the harvest‐based Bayesian estimation is effective in reducing the observation errors in sika deer populations, but the stage‐structured model requires many demographic parameters to be known prior to running the analyses. These parameters cannot be estimated from the observed time‐series of the index if there is insufficient data. We then construct a univariate model by simplifying the stage‐structured model and show that the simplified model yields estimates that are nearly identical to those obtained from the stage‐structured model. This simplification of the model simultaneously clarifies which parameter is important in estimating the population.

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We consider here a management policy for a sika deer (Cervus nippon) population in the eastern part of Hokkaido. Deer populations are characterized by a large intrinsic rate of population increase, no significant density effects on population growth before population crash, and a relatively simple life history. Our goals of management for the deer population are (1) to avoid irruption with severe damage to agriculture and forestry, (2) to avoid the risk of extinction of the deer population, and (3) to maintain a sustainable yield of deer. To make a robust program on the basis of uncertain information about the deer population, we consider three levels of relative population size and four levels of hunting pressures. We also take into consideration a critical level for extinction, an optimal level, and an irruption level. The hunting pressure for females is set to increase with the population size. We also recommend catching males if the population size is between the critical and optimal levels and catching females and males if the population size is larger than the optimal level. We must avoid cases of irruption or threatened population under various sets of uncertain parameter values. The simulation results suggest that management based on sex-specific hunt-ing is effective to diminish the annual variation in hunting yield.

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We evaluated relative density indices of sika deer (Cervus nippon) to aid in population management. We monitored sika deer population trends from 1992 to 2002 in the eastern part of Hokkaido Island, northern Japan, using spotlight surveys, aerial surveys, catch per unit effort (CPUE), sighting per unit effort (SPUE), and cost of damage to agriculture and forestry. We assumed that the artificial bias in the spotlight index would be lower than in other indices, and compared temporal patterns of other indices to those produced using spotlight surveys using model II regression. There was a significant correlation between the damage cost index and the spotlight index, and both indices indicated consistent population trends. Managers used CPUE as a tool to determine hunting quota efficiency. The SPUE index had the smallest standard error among the indices, and the spotlight survey index had the second smallest standard error. Overall, the spotlight survey was the most useful index because its estimate error was small and it was precise in showing population trends; however, spotlight surveys did lead to underestimation once in 1994. The SPUE index seems to be effective in checking the validity of the spotlight index, but there are so many environmental and demographic uncertainties that several independent indices should be used and crosschecked for accurate evaluation of population trends.

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The daily rhythms of formation and reingestion of hard and soft faeces were studied in Lepus brachyurus. Although the Leporidac have long been known to reingest soft faeces, the Japanese hare also reingests a substantial amount of hard faeces. All the faeces excreted during the daytime stay in a form, comprising first hard faeces, then soft faeces and again hard faeces, were reingested. Hares repeatedly sit straight up from the squatting position to practise reingestion. A reingestion bout for hard faeces consists of repeated faeces‐taking actions each followed by mastication, whereas that for soft faeces includes only one faeces‐taking action without mastication. If deprived of food during foraging at night, the Japanese hare reingested most of the faeces that were normally discarded. Evidence in literature indicates that other Leporidae also practise reingestion of hard faeces.