Grazing and Feeding Behaviors in Herbivores¶

Overview¶

This document summarizes research on grazing patterns, optimal foraging theory (Marginal Value Theorem), patch selection, feeding time budgets, and resource depletion responses in herbivorous mammals.

Key Findings¶

Grazing Patterns and Movement¶

Daily Grazing Patterns¶

• Cattle and sheep exhibit distinct bimodal grazing patterns with peaks in morning and afternoon, plus a pronounced midday rest period
• Horses graze more steadily throughout the day (50-80% of their time) without pronounced rest periods
• Consistent individual differences in cattle behavior suggest "grazing personalities" that persist over time

Daily distance traveled varies significantly: - Sheep: 2.85 km/day - Cattle: 1.68 km/day - Horses: 1.65 km/day

Factors Influencing Grazing Distribution¶

• Abiotic factors: slope, distance to water, terrain characteristics
• Biotic factors: forage availability and quality
• Resource heterogeneity in the environment
• Movement speed is lower in spring/winter with higher daily foraging percentages due to lower food resources and shorter daylight hours

Patch Selection and Optimal Foraging Theory¶

The Marginal Value Theorem (MVT)¶

Core Principle: Developed by Eric Charnov (1976), the MVT predicts when an animal should leave a resource patch to maximize overall energy intake rate.

Mathematical Rule: Foragers should abandon all patches once their instantaneous intake rate falls to the same marginal capture rate as the expected average rate across all patches in the environment.

Critical Variables: - Ti: Time spent in a given patch (residence time) - Interpatch travel time: Time moving between patches - Patch yield: Amount of resources obtained - Intake rate: Rate of resource acquisition within patch

Key Predictions: - Longer travel times between patches = longer optimal giving-up times (GUTs) - Leave patch when: instantaneous intake rate = long-term average habitat intake rate - Giving-Up Density (GUD): Quantifies forager's quitting harvest rate within a resource patch

Patch Size and Scale Effects¶

• Scale matters: WallisDeVries et al. (1999) demonstrated that patch size significantly affects herbivore selectivity (240+ citations)
• Sheep spend more time grazing smaller grass patches (1-6 m²)
• Red deer show no consistent grass patch size preferences
• As patch size and density decline, animals walk faster, crop larger bites, and take more bites per stem

Feeding Time Budgets¶

Diurnal Patterns (24-hour cycles)¶

• 90% of grazing time occurs during daytime
• 73% of ruminating time shows strong diurnal patterns
• Hour of day, season, and supplementary feed significantly affect grazing, rumination, and idling behaviors
• Sheep spend approximately 8.57 hours grazing on average during daylight
• Grazing and rumination time budgets remain similar across different forage types (pasture, chicory, silage)

Key Relationships¶

• Longer grazing time → higher intake → longer rumination time required for processing
• Idling time varies based on forage type
• Resting is integral to animal fitness through optimization strategies
• Restricting pasture access results in much greater grazing efficiency

Time Allocation Strategies¶

• Bimodal species (cattle, sheep): morning peak, midday rest, afternoon peak, nighttime rest
• Continuous grazers (horses): steady grazing throughout extended periods
• Seasonal variation: spring/winter show higher foraging percentages due to resource scarcity

Resource Depletion and Response¶

Giving-Up Density (GUD) Framework¶

• GUD experimentally quantifies forager's quitting harvest rate within a resource patch
• Animals should quit patches when benefit (harvest rate) no longer outweighs costs (including predation risk)
• Social rank influences giving-up density in group-feeding scenarios (e.g., bison studies)

Response to Depletion¶

• Herbivores become more selective during dry seasons to obtain high-quality forage
• Increased selectivity driven by metabolic requirements
• Plant quality and biomass variability significantly influence diet selection

Seasonal Changes in Grazing Behavior¶

Movement and Activity Patterns¶

• Movement speed: Lower in spring and winter, higher in summer
• Daily foraging percentage: Higher in spring/winter due to lower food resources and shorter daylight
• Grazing season effects: Highly significant effects on diurnal intake time, bite weight, dry matter intake, total steps, and chews per feed

Diet Selection Changes¶

• Mega and meso-herbivores: 25 forage plants constitute over 70% of diet year-round
• Consistent preferences: Despite seasonal differences, herbivores maintain preferences for adult leaves with more epiphytes and higher nitrogen content
• Pasture selection: Cows, mares, and ewes spend most grazing time on improved ryegrass-clover pasture regardless of season

Social Feeding Behavior¶

Social vs. Feeding Motivations¶

• Social grouping tendencies influence grazing behavior significantly
• Sheep more easily split into subgroups with familiar peers
• Two key factors for group-living herbivores:
• Feed availability
• Individual dominance status

Dominance and Foraging¶

• Dominance hierarchies impact foraging behavior
• Time of grain supplementation and social dominance interact to affect feeding patterns
• Grazing personalities (consistent individual differences) affect group distribution

Species-Specific Comparisons¶

Grazing Hierarchy (University of Idaho)¶

Competitive dominance: cattle > sheep > elk > mule deer > bighorn sheep > pronghorns > white-tailed deer

Species Comparison Table¶

Cattle¶

• Bimodal grazing pattern with distinct rest periods
• Prefer grasses over other forage types
• Higher soil compaction due to weight
• Moderate daily travel distance (1.68 km)
• Social dominance affects foraging in groups

Sheep¶

• More selective grazers than cattle
• Prefer smaller patches (1-6 m²)
• Longest daily travel distance (2.85 km)
• Lower soil impact due to lighter weight
• Form subgroups based on familiarity
• Less pasture damage compared to cattle and horses

Horses¶

• Longest grazing time (50-80% of day)
• Continuous grazing pattern without pronounced rest periods
• Hindgut fermenters (different digestive strategy than ruminants)
• High soil compaction
• Prefer grasses
• Shorter daily distance (1.65 km) despite longer grazing time

Deer (Wild Ungulates)¶

• Highly selective foragers
• No consistent grass patch size preferences (1 m² to larger areas)
• More flexible habitat use compared to domestic species
• Lower in grazing hierarchy when competing with livestock
• Migration patterns influence diet selection
• 25 key forage plants constitute >70% of diet

Rabbits¶

• Generally known to be highly selective grazers
• Create distinct grazing lawns through intensive localized grazing

Mathematical Models¶

Functional Response Models (Holling-based)¶

• Type II functional response: Intake rate increases with resource density but plateaus due to handling time
• Type IV functional response: Intake rate declines at very high resource densities (recently documented in plant-herbivore systems by Mezzalira et al., 2017)
• Intake rate formula: Function of bite size, bite rate, and forage density

Key Equations¶

Marginal Value Theorem:

Depart when: dTi/dt = average habitat intake rate

Functional Response (simplified):

Intake rate = f(bite size, bite rate, forage density, handling time)

Giving-Up Density:

GUD = initial resources - resources consumed when forager quits

Key Academic References¶

Foundational Papers¶

1. Charnov, E.L. (1976). "Optimal Foraging, the Marginal Value Theorem" (7,370+ citations)
2. Belovsky, G.E. (1984). "Herbivore Optimal Foraging: A Comparative Test of Three Models" (358 citations)
3. WallisDeVries, M.F., Laca, E.A., & Demment, M.W. (1999). "The importance of scale of patchiness for selectivity in grazing herbivores" (241 citations)
4. Pyke, G.H. (1977). "Optimal Foraging: A Selective Review of Theory and Tests" (4,561 citations)

Recent Research (2018-2025)¶

1. Mehdizadeh et al. (2023) - "Classifying Chewing and Rumination in Dairy Cows"
2. (2025) - "Activity and behavior patterns of cattle, horses, and sheep grazing in mountainous areas"
3. (2024) - "Consistent individual differences in cattle grazing patterns"
4. (2021) - "Holling meets habitat selection: functional response of large herbivores revisited"
5. Mezzalira et al. (2017) - "Mechanisms and implications of a type IV functional response"

Specialized Reviews¶

1. Tedeschi (2019) - "Mathematical modeling in ruminant nutrition: approaches" (78 citations)
2. (2023) - "Livestock feeding behavior: A tutorial review on automated techniques"

Implementation Notes for Minecraft Mod¶

Key Behaviors to Implement¶

1. Bimodal grazing: Animals graze in morning and afternoon, rest midday
2. Patch selection: Animals move between grass patches based on Marginal Value Theorem
3. Giving-Up Density: Animals leave depleted patches for fresh ones
4. Grazing personalities: Individual variation in grazing behavior
5. Social feeding: Dominant animals get access to best patches
6. Seasonal variation: Different grazing patterns by season

Configuration Parameters¶

Minecraft Entity Considerations¶

Vanilla animals that could benefit: - Cows, Sheep, Mooshroom: Bimodal grazing, patch selection - Rabbits: Selective grazing, creating grazing lawns - Horses (if added): Continuous grazing pattern - Goats: Similar to sheep, more selective

Behavior improvements: - Animals actually consume grass blocks over time (regenerate later) - Animals move between grazing areas, not just wander randomly - Dominant animals push subordinate animals from good grazing - Pregnant/nursing mothers have higher nutritional needs - Seasonal changes in grazing behavior (more grazing in "winter/spring" biomes)

Code Structure Suggestion¶

public class GrazingBehavior {
    private final double givingUpDensity;
    private final int patchSize;

    public void tick(AnimalEntity animal) {
        // Check if it's grazing time
        long dayTime = animal.level().getDayTime() % 24000;
        if (!isGrazingTime(dayTime)) {
            return; // Resting or not grazing time
        }

        // Check current patch quality
        BlockPos currentPos = animal.blockPosition();
        double patchQuality = assessPatchQuality(currentPos);

        if (patchQuality < givingUpDensity) {
            // Leave patch, find new one
            findNewPatch(animal);
        } else {
            // Continue grazing
            graze(animal);
        }
    }

    private boolean isGrazingTime(long dayTime) {
        // Bimodal: morning (0-6000) and afternoon (8000-12000)
        return (dayTime > 1000 && dayTime < 5000) ||
               (dayTime > 8000 && dayTime < 11000);
    }

    private double assessPatchQuality(BlockPos pos) {
        int grassBlocks = 0;
        int totalBlocks = 0;

        for (BlockPos check : BlockPos.betweenClosed(
            pos.offset(-patchSize, -1, -patchSize),
            pos.offset(patchSize, -1, patchSize))) {
            totalBlocks++;
            if (animal.level().getBlockState(check).is(Blocks.GRASS)) {
                grassBlocks++;
            }
        }
        return (double) grassBlocks / totalBlocks;
    }
}