Supplementary Feeding Experiment Research Articles

Changes in the amount and nutritive characteristics of annual pastures from late spring to autumn on the south coast of Western Australia

We examined declines in annual pasture dry matter on offer (DMO) from around peak accumulation in spring through summer-autumn in 14 supplementary feeding experiments across the south coast of Western Australia. Changes in dry matter digestibility (DMD) and concentrations of nitrogen, phosphorus, potassium (K), calcium, magnesium and sulfur were also measured. Plants which germinated in summer-autumn were manually separated, as far as possible, by removing green components from the dry material, and it was assumed all dry pasture had grown during the previous growing season. Measurements were made under grazing (stocking rates varying from 8 to 16.7 young wethers/ha) and in exclosures, and the experiments were carried out at 5 locations over 3 years. Within any experiment, there were no significant effects of supplementary feeding treatments on declines in DMO, DMD or digestible dry matter on offer (DDMO). Highest measured DMo and DMD varied from 2600 to 8600 kg DM/ha and from 63 to 8 I%, minimum measured values ranged from 100 to 1600 kg DM/ha and 45 to 54%, with amounts of DM0 lost varying from 2000 to 8500 kg DM/ha. The declines in DMO, DMD and DDMO under grazing through summer-autumn were described by exponential decay curves. Losses in DM0 and DDMO, as calculated from curve parameters, were positively correlated (P<0.001) with maximum DM0 or DDMO, respectively. Loss and average rate of loss in DMo were also correlated (P<0.01) with total rainfall through the period of measurement. The number of rainy days, stocking rate and botanical composition of pastures in spring were not significantly correlated with these losses under the conditions of these experiments. The percentage rate of decline in DM0 was not strongly correlated with any of these variables and its variation across experiments was small. Change and rate of change in DMD were positively correlated (P<0.001) with maximum measured DMD and negatively correlated (P<0.05) with the percentage of grass in the pasture. It was estimated that most of the lost material was not consumed by sheep. The concentrations of some essential minerals in grazed dry pasture approached, or fell below, their critical concentrations in most experiments. Of the minerals measured, only changes in K concentrations in dry pasture were well described by exponential regressions.

Food Supply, Territory Quality, and Reproductive Timing in the Blue Tit (Parus Caeruleus)

We performed supplemental feeding experiments during three breeding seasons of the Blue Tit (Parus caeruleus L.) in order to establish the importance of food in reproductive timing. In particular, we addressed the question of why the response to supplemental food is restricted to 3—6 d in many bird species. Supplemental food advanced the start of egg—laying in all three breeding seasons. The mean difference between fed and control pairs was 4 d in two years and 6 d in another. The amount and quality of the supplemental food used in the experiment were not limiting, since pairs receiving a further increase in amount and quality of food did not start laying earlier than pairs with a standard feeding regime. The amount of food that was consumed increased during the period from 15 d before egg formation until the beginning of egg formation and then remained at a high utilization rate until clutch completion. Although fed pairs, on average, started egg—laying earlier than control pairs, the earliest control females started to lay eggs as early as the first females. Fed pairs were also relatively late in a year when control pairs were late. In 1992, fed pairs did not produce larger clutches or more fledglings, but had nestlings with lower mass at 13 d post—hatching than those of control pairs. Analysis at the territory level revealed that supplemental food affected laying date to a greater extent in low—quality territories, in which laying could be advanced by up to 9—10 d, compared to high—quality territories in which laying was not advanced at all. We conclude that laying date in most Blue Tit females is limited by low food supply early in spring, but some females, occupying high—quality territories, will not advance laying in response to food. Thus, above a certain critical limit, laying date is unrelated to food supply, and birds use other cues in their decision to commence breeding. Such cues are probably also responsible for the between—year variation in laying dates of food—supplemented pairs, since these were provided with the same amount of food during the different years.

Experimental evidence for regulation of food delivey to storm petrel, Hydrobates pelagicus, nestlings: the role of chick body condition

The existence of a possible feedback mechanism, causally relating the nutritional status of nestling British storm petrels to the subsequent rates of food provisioning by their parents, was examined using a supplementary feeding experiment. There were no differences in parental provisioning behaviour between experimental and control groups before the supplementary feeding regime commenced. Thereafter, chicks receiving supplementary food showed higher levels of body condition (attributable to the experimental protocol), and consequently received smaller and less frequent meals from their parents than controls. The total amount of food received by the experimental group (parental delivery plus supplementary food) was similar to the amount delivered by control parents, indicating compensatory regulation of provisioning. These results support earlier findings at the same colony but are in contrast to similar studies on other procellariiform species elsewhere. The demonstration of regulation of food delivery casts doubt on hypotheses relating slow growth and lipid accumulation of procellariiform nestlings to scarce and unpredictable food resources, and indicates that more recent explanations relating lipid deposition to chronic overprovisioning by the adults are untenable for this species.

Avian reproductive timing: when should parents be prudent?

Based on the differing costs and benefits of early breeding, single-brooded parent birds are expected to be prudent, and base their decision to commence breeding on several reliable cues in addition to their energy balance, in contrast to multi-brooded parents. A comparative study using data from supplemental feeding experiments performed on 16 species of birds from 12 genera supported this prediction. The multi-brooded birds advanced their laying dates to a greater extent following food provisioning than the double- and single-brooded birds. The response to food was not affected by female body mass or length of the pre-feeding period, indicating that the differences between species do not simply reflect different metabolic needs of birds differing in size, and that experimental differences in set-up are unlikely to confound the results. Advancement of laying was significantly related to the length of the egg-laying period, but this was mainly due to the strong responses and long breeding seasons of the multi-brooded birds. The results suggest that different birds have different reproductive windows, and some possible factors that might influence the timing of breeding are discussed.

The Effect of Variation in the Laying Interval on Proximate Determination of Clutch Size in the European Kestrel

I propose that if laying interval varies depending on daily energy intake, then laying interval should also play a basic role in the determination of clutch size. A supplemental feeding experiment with European Kestrels Falco tinnunculus was performed to test this hypothesis. Supplemented females laid larger clutches with shorter intervals between eggs than control females, but did not take longer to complete their clutches. Clutch size was negatively correlated with mean laying interval. Clutch size also declined seasonally, but the effect of laying date disappeared when laying interval was controlled for statistically. Therefore, food supply affected clutch size through laying interval, not through laying date.

Proximate determination of clutch size in lesser black-backed gulls: the roles of food supply and body condition

Though many authors have demonstrated an adaptive relationship between food supply or territory quality and clutch size, the proximate mechanism by which clutch size is determined remains largely unknown. A series of supplementary feeding experiments on lesser black-backed gulls (Larus fuscus) is used in conjunction with a new technique to measure pectoral muscle protein levels in live birds to investigate the relationships between food supply, body condition, and clutch size. Comparisons across treatments revealed a positive relationship between the level of flight muscle protein at the start of laying and clutch size, but not egg size. In a year when the clutch sizes of unfed birds were reduced, suggesting low food availability, gulls provided with a protein supplement had higher levels of flight muscle protein at the start of laying and laid larger clutches than birds that received no food supplement. In contrast, gulls provided with an additional energy source (fat) did not attain higher protein levels or lay larger clutches than unfed gulls. In a second year, when unfed gulls laid larger clutches, which were typical for the species, supplements of two different protein types (fish and egg) had no effect on clutch size, though egg-fed females laid considerably (10%) larger eggs. However, there were no detectable differences in condition between treatments at the start of laying, suggesting that though flight muscle protein levels may be of importance in determining clutch size, they may be of lesser significance for egg size, which may be largely influenced by dietary intake.

Variation in laying date, clutch size, egg size, and egg composition of yellow-headed blackbirds (Xanthocephalus xanthocephalus): a supplemental feeding experiment

I studied the effects of food availability, habitat quality, and timing of breeding on egg production in yellow-headed blackbirds (Xanthocephalus xanthocephalus). Food availability was experimentally manipulated by providing females on six wetlands with supplemental food; six additional wetlands served as unsupplemented controls. Mean nest initiation dates varied by up to 6 d among wetlands, and supplementally fed blackbirds initiated nests 2 d earlier than controls, on average (although this latter difference was not quite significant; P = 0.07). Clutch size declined with laying date, but was unaffected by wetland location, food supplementation, or interactions between these two factors and laying date. Although egg size did not vary among wetlands or in relation to supplemental feeding, egg composition varied with both of these factors. All egg components except wet and dry shell and dry albumen varied among wetlands, whereas total water, wet yolk, and lean yolk were the only components that varied with food supplementation. Large blackbird eggs contained proportionately more water and albumen, but proportionately less yolk and shell. These patterns were somewhat compensatory, such that proportional protein and energy content did not vary with egg size; however, large eggs contained proportionately less fat than did small eggs. Proportional egg composition varied among wetlands (yolk and energy content), but was not affected by supplemental feeding. In general, egg production by yellow-headed blackbirds was not greatly affected by food availability. This may have been due to any of the following four factors: (1) inaccessibility of food supplements owing to competition between male and female blackbirds, (2) insufficient time for females to respond to food supplements, owing to rapid settlement and nest initiation, (3) a nutritionally inappropriate food supplement (i.e., protein availability may not have been enhanced among fed birds), or (4) superabundance of natural foods such that food availability was not limiting egg production.

Nutritional Constraints on Egg Formation in the Lesser Black-Backed Gull: An Experimental Study

The use of supplementary feeding experiments to investigate the relationship between food supply and clutch and egg size in birds has yielded disparate results, some authors showing an advancement in laying date and/or increased clutch size in response to additional food whereas other studies have found no effect. Here we investigate the nutritional requirements of egg formation in lesser blackbacked gulls Larus fuscus L., through a series of feeding experiments providing additional food of different quality

Long-term Population Trends in White-Footed Mice and the Impact of Supplemental Food and Shelter

Central to most models of population regulation is the idea that the degree of intraspecific competition is in some way proportional to the availability of limiting resources. Although laboratory research has demonstrated a number of proximate mechanisms by which behavior might affect population growth, little is known about the resources that are actually limiting population density in the field or about how animals might compete for them. Long-term field studies reveal that the white-footed mouse, Peromyscus leucopus , exhibits two types of pronounced changes in density: intra-annual (seasonal) and inter-annual. The former seem to be due ultimately to climate and the lack of winter breeding, but populations often decline sharply in late summer in the midst of plentiful food; fall recruitment of new animals is density-dependent and usually poor. Differences in peak densities from one year to the next as high as 13-fold have been recorded. Weather, shelter, and food are possible ultimate limiting resources. Food has received themost attention, but supplemental feeding experiments have yielded mixed results. A review of the social behavior of this polygnous species suggests that each sex is limited by different combinations of factors. Females may defend a food source and nest sites; males may search actively for females at low adult densities, covering large areas, and defend access to females at high adult densities. Additional long-term field studies are needed, both to provide direction to laboratory research on proximate mechanisms and to provide the data base for understanding the role of weather, food, and shelter as ultimate limiting factors. Enough short-term studies have been published to permit comparisons across habitats and through time which will give a better perspective on climate and habitat variables. Field experiments are necessary to demonstrate the operation of proximate behavioral, physiological, and genetic mechanisms of population regulation in natural populations.

Food availability affects growth in a coral reef fish.

Pomacentrus amboinensis is common on small patch reefs within One Tree Lagoon (Great Barrier Reef), where it preferentially settles onto deep reefs. A preliminary experiment, in which juveniles were transplanted to identical reef structures at two sites, within two depth strata, indicated that juvenile growth and survivorship were better in deeper water. The hypothesis that this difference was due to food availability was tested by a supplemental feeding experiment, carried out at another two randomly chosen sites, within the same two depth strata. Fish were fed each day over a one month period, during which no mortality was observed. The growth rates of juveniles were markedly higher on all food-supplemented reefs, when compared to controls. Growth differed between depth strata, but there was no interaction between the food x depth factors, which would have suggested a greater effect of food supplementation in either habitat. Thus, although the difference between depths cannot be attributed to food availability, the results have a more general significance. Food appears to be a limiting resource (in terms of growth) in both the marginal shallow habitat, and the more suitable deeper habitat.

The combined effects of temperature and salinity on hatching success and the survival, growth, and development of the larval stages of Metapenaeus bennettae (Racek & Dall)

During the spawning season of the estuarine prawn Metapenaeus bennettae (Racek & Dall), laboratory and field experiments were conducted to examine the combined effects of temperature and salinity on hatching success of eggs and the survival, growth and development of larvae. Response surface analysis showed that optimal levels of temperature and salinity for maximum hatching success varied depending on conditions during spawning. Similarly, temperature and salinity conditions that produced maximum survival and growth of larvae depended on conditions during rearing prior to experimental temperature/salinity treatments. At the onset of feeding, larvae showed the lowest tolerance to changes in temperature and salinity. Supplementary feeding experiments in the laboratory, and survival rates in field experiments indicated that starvation was a more potent factor than the effects of temperature and salinity in determining survival through the protozoeal larval stages. Late larval stages were relatively indifferent to the effects of temperature and salinity. It is suggested that, during early development, adaptive response to the prevailing physical conditions enhances survival in an estuarine environment.

Common-Range Technique in Supplemental Feeding Experiments

Common-Range Technique in Supplemental Feeding Experiments