Food supplementation experiments revisited: verifying that supplemental food is used by its intended recipients

Field-based food supplementation experiments can determine whether populations are limited by natural food availability. However, they may yield spurious results if added food is hoarded by dominants, exploited by immigrants, or delivered ineffectively. Surprisingly, population-level approaches accounting for these potential sources of bias have not been established. We explored responses of free-ranging snowshoe hares ( Lepus americanus Erxleben, 1777) to food supplementation by contrasting per capita browsing rates on three study sites with added food with those on three control sites during two winters. Food augmentation reduced foraging pressure by hares; this reduction was significant when browse species of high dietary importance were considered. By implication, hares on manipulated sites switched from favored natural foods to supplemental food, meaning that the extra food found its mark and was not heavily exploited by immigrants or hoarded by dominants. Demographic responses to food addition were not detected on the manipulated sites, indicating that the study population was not food limited. Given the success with which we detected the signal of supplementation and eliminated potential confounding factors, we suggest that future studies using food addition in the context of herbivore population dynamics would benefit from a more mechanistic approach; this may involve measurement of browsing rates on manipulated and control sites.

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Differential sex-related winter energetics in free-ranging snowshoe hares (Lepus americanus)

Canadian Journal of Zoology ◽

10.1139/cjz-2015-0074 ◽

2016 ◽

Vol 94 (2) ◽

pp. 115-121 ◽

Cited By ~ 3

Author(s):

E. Ellsworth ◽

M.R. Boudreau ◽

K. Nagy ◽

J.L. Rachlow ◽

D.L. Murray

Keyword(s):

Energy Expenditure ◽

Food Availability ◽

Lepus Americanus ◽

Energetic Cost ◽

Food Supplementation ◽

Natural Food ◽

Daily Energy Expenditure ◽

Snowshoe Hares ◽

Daily Energy ◽

Free Ranging

Animals spend considerable time and energy acquiring food to meet their metabolic requirements, but if energetic or fitness costs are substantive, such as during winter, then some individuals may limit daily energy expenditure by reducing foraging duration. To date, the prevalence and magnitude of such compensatory foraging responses are poorly known. We examined energy balance compensation in free-ranging snowshoe hares (Lepus americanus Erxleben, 1777) via a food supplementation experiment to determine whether individuals reduced their daily energy expenditure (DEE) and activity periods in response to increased food availability. Overall, food supplementation had no effect on diel activity patterns, although males had higher DEE compared with females. During early and mid-winter, hares did not alter their activity periods in response to food supplementation, but during late winter, when natural food availability declined, food-supplemented females (but not males) were ∼11% less active compared with controls. Natural food likely was sufficient and could have been acquired at relatively low energetic cost, but because males likely have higher DEE due to mating behavior whereas females may limit their activity (and thus DEE) to reduce predation risk, we conclude that gender-specific life-history demands can over-ride predicted responses to supplemental food when baseline food abundance is adequate.

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Effects of Supplemental Food on the Behaviour and Paternity Status of Male Indigo Buntings (Passerina CyaNea)

Avian Biology Research ◽

10.3184/175815618x15203297120204 ◽

2018 ◽

Vol 11 (2) ◽

pp. 67-73

Author(s):

Brad T. McLeod ◽

Gary Ritchison

Keyword(s):

Time Budget ◽

Mate Guarding ◽

Breeding Birds ◽

Food Supplementation ◽

Time Budgets ◽

Blood Samples ◽

Supplemental Food ◽

Extra Pair Paternity ◽

Passerina Cyanea ◽

And Control

Breeding is energetically costly and, if energy-limited, birds may alter their time budgets, spending less time engaged in some activities and more time in others. Investigators who have provided breeding birds with supplemental food have noted changes in time budgets, but the extent and types of changes have been found to vary among species. Our objective was to determine how food supplementation might influence the time budgets and paternity status of male Indigo Buntings (Passerina cyanea). We studied Indigo Buntings from 8 May to 15 August 2009 in Madison County, Kentucky. Territories of male Indigo Buntings (n=30) were randomly assigned as either food supplemented (n=8) or controls (n=22). During time-budget observations, all behaviours were noted. To determine paternity status, blood samples were collected from adults and nestlings at 16 nests. Males with feeders in their territories spent significantly less time foraging and more time vocalising (chip notes) than males without feeders. Time spent singing and mate guarding by treatment and control males did not differ. Differences in the proportion of extra-pair young did not differ between nests in territories with and without supplemental food. Our results suggest that, when provided with supplemental food, male Indigo Buntings spend less time foraging and more time engaged in other activities. However, neither the presence of supplemental food nor differences in the behaviour of males in food-supplemented versus non-supplemented territories affected rates of extra-pair paternity.

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Food supplementation experiments with terrestrial vertebrates: patterns, problems, and the future

Canadian Journal of Zoology ◽

10.1139/z90-031 ◽

1990 ◽

Vol 68 (2) ◽

pp. 203-220 ◽

Cited By ~ 552

Author(s):

Stan Boutin

Keyword(s):

Population Level ◽

Fold Increase ◽

Food Supplementation ◽

Home Ranges ◽

Small Spatial Scale ◽

Supplemental Food ◽

Terrestrial Vertebrates ◽

Tropical Environments ◽

Body Weights ◽

Fluctuating Populations

I reviewed 138 cases in which terrestrial vertebrates received supplemental food under field conditions. These cases are strongly biased toward small-bodied herbivores in north temperate environments. Most studies address population level questions and have supplied food over a short term (< 1 year) and on a small spatial scale (to less than 50 individuals). Individuals receiving supplemental food usually had smaller home ranges, higher body weights, and advanced breeding relative to those on control areas. The typical population response to food supplementation was two- to three-fold increase in density, but no change in the pattern of population dynamics. In particular, food addition did not prevent major declines in fluctuating populations. Researchers have failed to examine behaviour of individuals under conditions of supplemental food when addressing questions of population regulation. This review points to the need for researchers to conduct food supplementation experiments in tropical environments, on a larger scale, and over longer periods of time.

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Survival of juvenile hares during a cyclic population increase

Canadian Journal of Zoology ◽

10.1139/z98-136 ◽

1998 ◽

Vol 76 (10) ◽

pp. 1949-1956 ◽

Cited By ~ 10

Author(s):

Elizabeth A Gillis

Keyword(s):

Cause Of Death ◽

Food Availability ◽

Survival Rates ◽

Lepus Americanus ◽

Population Increase ◽

Differential Survival ◽

Proximate Cause ◽

Supplemental Food ◽

Snowshoe Hares ◽

And Control

Snowshoe hares (Lepus americanus) are multilittered synchronous breeders that produce up to four distinct litters of young each summer. I used radiotelemetry to determine the effects of juvenile cohort (i.e., litter group) and food availability on postweaning survival of hares in the southwestern Yukon during the increase phase of a hare cycle. During the study, I monitored 86 juvenile hares from control areas and areas in which supplemental food was provided. Twenty-eight-day survival did not differ between food addition and control areas for any juvenile cohort, and survival rates of juveniles (all cohorts combined) did not differ significantly from those of adults (juveniles: 0.91 per 28 days; adults: 0.93 per 28 days). However, when examined by juvenile cohort, survival of third and fourth litters was significantly lower than that of adults and first and second litters. These differences were the result of differential survival among the juvenile cohorts during a 3-month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% of deaths.

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Food shortage for breeding Black-billed Magpies (Pica pica): an experiment using supplemental food

Canadian Journal of Zoology ◽

10.1139/z87-198 ◽

1987 ◽

Vol 65 (5) ◽

pp. 1270-1274 ◽

Cited By ~ 36

Author(s):

Wesley M. Hochachka ◽

David A. Boag

Keyword(s):

Breeding Population ◽

Egg Laying ◽

Food Shortage ◽

Laying Date ◽

Food Supplementation ◽

Natural Food ◽

Supplemental Feeding ◽

Pica Pica ◽

Supplemental Food ◽

Before And After

Supplemental food was provided to a breeding population of Black-billed Magpies (Pica pica), starting before and after eggs were laid, to determine if and when natural food was limited. The production of fledgling magpies was increased only when supplemental feeding was begun before laying. Laying date was also advanced when supplemental feeding began before laying, but clutch and egg size were not significantly changed. Because the two feeding treatments were conducted in different years, we cannot conclude whether natural food was limiting before or after egg laying. However, out data suggest that the former may have been the case. An improved design for food supplementation experiments, which can be used to determine the time of food shortage, is suggested.

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Effect of supplemental cover on survival of snowshoe hares and cottontail rabbits in patchy habitat

Canadian Journal of Zoology ◽

10.1139/z97-761 ◽

1997 ◽

Vol 75 (9) ◽

pp. 1357-1363 ◽

Cited By ~ 16

Author(s):

Eric W. Cox ◽

Robert A. Garrott ◽

John R. Cary

Keyword(s):

Effective Means ◽

Protective Role ◽

Range Limits ◽

Sylvilagus Floridanus ◽

Fragmented Habitat ◽

Snowshoe Hares ◽

Patchy Habitat ◽

Study Sites ◽

And Control

We examined mortality patterns of sympatric snowshoe hares (Lepus americanus) and cottontail rabbits (Sylvilagus floridanus) on sites with and without brush piles to evaluate the protective role of cover in the fragmented habitat typical at the range limits of both species. Treatment sites received ≥2 oak brush piles per hectare in August and September 1994. Leporids used a minimum of 56% of created brush piles, but we failed to detect a difference in survivorship between animals occupying treatment and control sites, suggesting that brush piles may not have served as effective refugia to leporids of either species. Coyotes (Canis latrans) killed leporids in understory cover similar in mean density to that of study sites, whereas raptor kills occurred in areas with sparser understory than the average for the study sites or at coyote kills. We concluded that other methods of habitat alteration may be more effective means of increasing numbers of snowshoe hares and cottontail rabbits.

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Does predation risk cause snowshoe hares to modify their diets?

Canadian Journal of Zoology ◽

10.1139/z03-192 ◽

2003 ◽

Vol 81 (12) ◽

pp. 1973-1985 ◽

Cited By ~ 20

Author(s):

K E Hodges ◽

A R.E Sinclair

Keyword(s):

Species Composition ◽

Predation Risk ◽

Sublethal Effects ◽

Population Cycle ◽

Food Supplementation ◽

Snowshoe Hare ◽

Supplemental Food ◽

Snowshoe Hares ◽

Wide Range ◽

Mammalian Predators

Snowshoe hares (Lepus americanus) undergo a 10-year population cycle with several years of low densities. Several authors have suggested that snowshoe hares modify their foraging behaviour to reduce predation risk during the low phase, resulting in protein-poor diets and poor body condition. We test that idea by using a factorial manipulation of food supplementation and predator reduction and by examining the species composition, browse size, and nutritional quality of snowshoe hare diets during 3 years of low snowshoe hare abundance in southwestern Yukon. Our results negate the hypothesis that snowshoe hares change their diets in response to mammalian predators during the cyclic low phase. Snowshoe hares on the different treatments had diets that differed in species composition and twig sizes, but protected hares did not have higher protein diets than unprotected hares. Snowshoe hares with access to supplemental food ate more fibrous and lower protein natural browse than unfed hares, showing that they did not choose diets primarily for protein content. Instead, snowshoe hares converted a wide range of forage availabilities into similar intakes of protein and fibre, despite variation in predator presence. Our results suggest that snowshoe hares select their diets to balance the protein and fibre contents. Although sublethal effects of predators may influence cyclic dynamics, our results show that such a feedback does not occur via a nutritional mechanism, counter to previous suggestions.

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The efficacy of anthelmintic treatment on the parasite abundance of free-ranging snowshoe hares

Canadian Journal of Zoology ◽

10.1139/z96-177 ◽

1996 ◽

Vol 74 (9) ◽

pp. 1604-1611 ◽

Cited By ~ 12

Author(s):

Dennis L. Murray ◽

Lloyd B. Keith ◽

John R. Cary

Keyword(s):

Propylene Glycol ◽

Control Sample ◽

Nematode Species ◽

Parasitic Nematodes ◽

Wild Mammals ◽

Snowshoe Hares ◽

Nematode Abundance ◽

Study Sites ◽

Free Ranging ◽

Nematodirus Triangularis

We examined the efficacy of an anthelmintic agent (ivermectin, Merck–Agvet) on the parasitic nematodes of free-ranging snowshoe hares (Lepus americanus) during 27 months in southern Manitoba. Marked hares on six 25-ha sites were injected bimonthly with ivermectin (treatment, n = 134) or propylene glycol (control; n = 149) and carcasses were necropsied to determine prevalence and intensity of Obeliscoides cuniculi, Nematodirus triangularis, Trichuris leporis, Dirofilaria scapiceps, and Protostrongylus boughtoni. We supplemented the control sample with hares (n = 175) captured off the study sites and not given propylene glycol. Mean prevalence (percentage of hosts infected) and intensity (number of parasites among infected hosts) of each nematode species decreased after treatment and were 35 – 85% lower than controls after 20–40 days. Treatment significantly reduced prevalence of D. scapiceps and P. boughtoni for about 50 days and of O. cuniculi and N. triangularis for longer periods. Overall intensity of O. cuniculi, N. triangularis, and P. boughtoni was significantly lower in treated than in control hares, and intensity of D. scapiceps was marginally (P < 0.10) lower for 50 days post treatment. Total reductions in nematode abundance (prevalence × intensity) ranged from 29 to 88% among the five species. Neither prevalence nor intensity of ticks (Haemaphysalis leporispalustris) was reduced following treatment. We conclude that ivermectin is effective at controlling nematodes in snowshoe hares but that its efficacy is variable among species. We use our results as a basis for discussing the applicability of anthelmintics to the conservation and management of free-ranging wild mammals.

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Menadione nicotinamide bisulphite as a source of vitamin K and niacin activities for the growing pig

Animal Science ◽

10.1017/s135772980005493x ◽

2000 ◽

Vol 71 (1) ◽

pp. 111-117 ◽

Cited By ~ 5

Author(s):

M. Marchetti ◽

M. Tassinari ◽

S. Marchetti

Keyword(s):

Vitamin K ◽

Control Diet ◽

Live Weight ◽

Organic Salt ◽

Free Form ◽

Food Supplementation ◽

Sodium Bisulphite ◽

Chemical Factors ◽

And Control ◽

Physical And Chemical

AbstractWhen compared with other menadione derivatives such as menadione sodium bisulphite (MSB), menadione nicotinamide bisulphite (MNB), an organic salt combining menadione and nicotinamide, shows better stability towards physical and chemical factors once it is added to pre-mixes or foods. The present work evaluates the bioavailability of the two vitamins present in this compound and toxicity in the pig. To assess vitamin bioavailability, pigs were given small amounts of food containing MNB or equivalent amounts of MSB and nicotinamide in the free form. Menadione and nicotinamide concentrations in blood samples drawn at set times after the diets were given did not reveal any significant differences between the two modes of administration. Haematic levels of both vitamins in animals receiving MNB, or MSB and nicotinamide, were after 2, 4, 8 and 12 h higher (P < 0·001) than those of untreated animals. The tolerance level to MNB was evaluated in pigs given diets containing graded amounts of MNB (100, 500, 2500 mg/kg) for 28 days. No significant (P > 0·05) differences were recorded in live weight, food intake and gain/food ratio in pigs given these diets when compared with those given an unsupplemented diet. Haemoglobin and bilirubin levels did not differ between animals given various amounts of MNB and control animals. Plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in pigs given 100 mg/kg of MNB did not show significant differences when compared with those observed in pigs given an unsupplemented control diet. In pigs on the diets supplemented with 500 and 2500 mg/kg of MNB there was a significant increase in the two enzymatic activities as compared with controls (P < 0·001 and P < 0·01). In the case of ALT this had disappeared by 28 weeks. MNB is a good source of vitamin K for the pig and does not appear to have any adverse effects, even when administered at levels higher than those normally used in pig food supplementation.

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