Decrease In Food Supply Research Articles

Foraging behaviour of Blue Tits Parus caeruleus in a patchy environment under contrasting levels of natural food supply

We analysed the foraging behaviour of free-ranging Blue Tits Parus caeruleus in open holm oak Quercus ilex woodlands of western Spain during winter. Such woodlands are patchy for foraging tits because of the scattered distribution of trees and the patterns of abundance of canopy arthropods within and among trees. Results were compared with those obtained in spring of the same year, when we found that the foraging behaviour and spatial distribution of Blue Tits were largely unaffected by food availability (Pulido and Díaz 1997). Patch (tree) residence time was highly variable both within and among individual birds, and it was uncorrelated with either previous travel time or patch quality. Contrary to a priori expectations, the behaviour of tits did not conform to short-term energy maximizing rules in winter, in spite of a 2.5-fold decrease in food supply from spring to winter and a likely 2-fold increase in bird requirements. Instead, birds tended to fly towards patches that were further away than locally available. Overall, we conclude that energy intake rate was not the fitness-related currency that birds were trying to maximize while foraging.

A comparative study of feeding and growth in two coexisting species of carnivorous gastropods

The effects of variable food supply on growth rate and feeding behaviour in two coexisting intertidal gastropods were examined through field and laboratory experiments involving mark and recapture procedures, growth experiments under controlled food supply and video observations of feeding. All cohorts of both Japeuthria species grew most in summer, with the highest growth rate being achieved by the youngest cohort of both sexes. In contrast, almost all cohorts (except the youngest one) showed zero to negative growth in winter. The growth rates of Japeuthria species clearly varied depending on feeding frequencies and the initial size of individuals. Females of both species had a significantly higher growth rate than males, though the difference became less marked with decreasing food supply. The total time spent on feeding and the length of the first feeding bout generally increased as the duration of the interval between meals was increased across treatments. From both the field growth experiment and the observations of feeding behaviour it is clear that J. ferrea had a higher frequency of feeding than J. cingulata in the field; 1- to 3-d intervals of feeding frequency in the former and 3- to 6-d intervals in the latter. Most notably, the two species showed a reversal in growth rates with changing conditions of food supply. When food was relatively abundant J. ferrea achieved better growth than J. cingulata, but J. cingulata grew better than J. ferrea under low food supply. In view of the fact that J. ferrea seems to be competitively superior to J. cingulata under normal levels, the present observation that J. cingulata can perform better than J. ferrea when food availability is low gives an important advantage to the latter in terms of its coexistence with the former.

Variation in structure and biomass of the benthic communities at three contrasting sites in the tropical Northeast Atlantic

Three major size classes of the benthic metazoan communities (megafauna, macrofauna and meiofauna) were investigated simultaneously at 3 sites in the tropical Northeast Atlantic. The sites varied in their level of surface primary productivity (eutrophic, mesotrophic and oligotrophic). Results for 3 cruises in 3 seasons (Eumeli 2, winter 1991; Eumeli 3, autumn 1991; Eumeli 4, spring 1992) are given for each size class in terms of taxonomic composition, density and biomass. The benthic communities did not exhibit evidence of seasonal variation, but there were substantial differences in the quantitative structure of the metazoan communities between the 3 sites. Total metazoan density and biomass, as well as density and biomass of each size class, decreased with increasing depth and decreasing food supply, suggesting that food limitation is the major factor controlling benthic standing stocks. The comprehensive study across the 3 major benthic metazoan size classes reveals that each component responds differently to the variation in food input, leading to a variation in the quantitative structure of the benthic metazoan fauna. The largest size class, megafauna, dominated biomass when the food input was high (eutrophic site), macrofauna was predominant in intermediate conditions (mesotrophic site), and meiofauna dominated where the food input was the lowest and depth the greatest (oligotrophic site). However, within a single size group, some taxa did not follow the trend of decreasing biomass with decreasing food supply, suggesting that food availability is not the only factor governing the structure of the benthic fauna. The influence of abiotic and biotic factors likely to affect the benthic communities was analysed. Physical conditions and biological features can also play a significant role in structuring abyssal fauna.

Why did the Prince William Sound, Alaska, Pacific herring (Clupea pallasi) fisheries collapse in 1993 and 1994? Review of hypotheses

Following record harvests of Pacific herring (Clupea pallasi) in Prince William Sound, Alaska, in the 3 years after the Exxon Valdez oil spill, the fishery failed in 1993. The hypotheses advanced to explain this dramatic 1993 decline occur in three categories: (i) effects associated with the 1989 oil spill, (ii) harvesting effects, and (iii) natural phenomena. Based on our review, we are convinced that a combination of increasing Prince William Sound herring biomass and decreasing food supply led to poor condition of Prince William Sound herring, which resulted in the 1993 decline. Other natural causes could have contributed to the decline, including disease, cold water temperatures, increased predation, and other natural stochastic processes. No evidence supports hypotheses that the decline resulted solely from overharvesting or underharvesting. The record high population levels and harvests of Prince William Sound herring in the years after the 1989 oil spill, the lack of change from the expected age-class distribution, and the low level of oil exposure documented for herring in 1989 and the following years all indicate that the 1989 oil spill did not contribute to the 1993 decline. Poor nutritional status, either alone or in combination with disease or other natural factors, was most likely responsible for the 1993 collapse.

Haematozoan Infections in the Eurasian kestrel: Effects of Fluctuating Food Supply and Experimental Manipulation of Parental Effort

The influence of parental effort on susceptibility to parasitism was investigated experimentally in the Eurasian kestrel (Falco tinnunculus) in Finland. Parental effort was manipulated by either enlarging or reducing broods by 1-2 young, while unmanipulated broods served as controls. This was done during 3 breeding seasons, during which the densities of the major prey of kestrels (voles) were relatively low, high and intermediate, respectively. Two, taxon specific, methods were applied for determining the prevalence (per cent individuals infected) of extracellular Trypanosoma spp. and intracellular Haemoproteus spp. infection. Blood samples were taken from females during the incubation phase, and from both parents during the mid-nestling phase. Trypanosoma was more prevalent when food was less available. Furthermore, the increase in the prevalence of Trypanosoma among females was most pronounced during the poor vole year. In contrast, Haemoproteus infection seemed not closely related to annual supply of main prey. Manipulations of parental effort were related to parental infection, but the effect differed between genders. The prevalence of Trypanosoma in males (main provider of young) increased with experimental brood size, and there was an interaction between food supply and brood size manipulation so that the difference in prevalences between reduced and enlarged broods increased with decreasing food supply. Among females, no such an interaction was found. Instead, the effect of brood enlargement on Trypanosoma prevalence of females was apparent in the pear of relatively high vole densities only. Manipulation of brood size did not have clear effects on Haemoproteus infection in either gender. These results support the idea that increased parental effort may make hosts susceptible to haematozoan infection, and are the first to suggest that resource levels (food supply) can modify the susceptibility, indicating that the magnitude of reproductive costs can be attributed to Variation in environmental conditions.

Effects of food supply on size at first maturity, fecundity and growth of hybrid tilapia, Oreochromis niloticus (L.) x Oreochromis aureus (Steindachner), in outdoor concrete tanks in Saudi Arabia

The effects of four levels of food supply (0.5%, 1%, 2% and 3% body weight daily) were investigated on some reproductive traits and growth of hybrid tilapia in outdoor concrete tanks. Fast-growing fish matured early in the season (March), but spawning started late in May. Smallest size of males and females at first maturity was 8.1 cm. Fish size at maturity appears to be influenced by the feeding level, which affects the growth of fish. For both sexes, no significant difference was found in gonadosomatic index (GSI) among different treatments. Mean percentage of mature fish decreased with decreasing food supply and was found to be significantly different between fishes fed at 3% (46%) and 0.5% (28%) body weight. Fecundity increased with increased feeding levels, although significant differences were found only between 3% and other feeding rates (0.5–2.0%). The fecundity per g female was higher at the lower ration levels (0.5% and 1%) than at the higher feeding levels. Egg quality, with respect to egg size, hatchability. fry length and weight, was not affected by the feeding rates. Final mean weight and food conversion ratios were significantly influenced by feeding rates. Higher increase in ovary weight with increasing body weight of mature females fed at 0.5% body weight than fishes receiving higher food levels suggests that in these fish, more food resources are diverted towards gonad building than to somatic growth.

Two neuronal G proteins are involved in chemosensation of the Caenorhabditis elegans Dauer-inducing pheromone.

Caenorhabditis elegans uses chemosensation to determine its course of development. Young larvae can arrest as dauer larvae in response to increasing population density, which they measure by a nematodeexcreted pheromone, and decreasing food supply. Dauer larvae can resume development in response to a decrease in pheromone and increase in food concentration. We show here that two novel G protein alpha subunits (GPA-2 and GPA-3) show promoter activity in subsets of chemosensory neurons and are involved in the decision to form dauer larvae primarily through the response to dauer pheromone. Dominant activating mutations in these G proteins result in constitutive, pheromone-independent dauer formation, whereas inactivation results in reduced sensitivity to pheromone, and, under certain conditions, an alteration in the response to food. Interactions between gpa-2, gpa-3 and other genes controlling dauer formation suggest that these G proteins may act in parallel to regulate the neuronal decision making that precedes dauer formation.

The significance of growth in Chironomus tentans sediment toxicity tests: Relationship to reproduction and demographic endpoints

AbstractIn the Chironomus tentans 10‐d growth test, changes in larval growth relative to sediment contamination are often ascribed ecological relevance by assuming that such changes become manifest at the population level through effects on reproductive output even though the relationship between growth and reproduction is poorly understood. The objective of this study was to evaluate the relationship between growth and reproduction in C. tentans and to use these data in a demographic model to predict the growth and size of a theoretical population. Growth was manipulated by varying food supply (0.29, 0.33, 0.38, 0.42, 0.46, and 0.5 mg/individual per d). The test was initiated with 12 newly hatched larvae per replicate and carried through one complete generation. Larval growth and survival were determined at 20 d, and reproduction was monitored daily during emergence. Food supply did not significantly affect survivorship at any life stage; survival of larvae at 20 d, pupae, and adults exceeded 83%, while survival of larvae in the reproduction replicates exceeded 65%. Both larval and adult dry weight declined significantly with a reduction in food supply. Total emergence was reduced at the lowest feeding level only, whereas the rate of emergence declined at food supplies below 0.42 mg/individual per d. Based on the relationship between larval and adult dry weight, a minimum larval tissue mass of between 0.5 and 0.6 mg dry weight/individual appears to be necessary before emergence can take place. The number of eggs/female declined significantly with a decrease in food supply below 0.42 mg/individual per d. Above this level (corresponding to larval dry weight of ∼ 1.5 mg/individual), the addition of more food had no effect on reproductive output. Fecundity (number of daughters/female) and expected number of progeny declined linearly with reduced food supply. Application of the data in a demographic model showed that the growth and predicted size of a population would decline significantly with a decline in larval growth and reproductive output. These results demonstrate that changes in growth, positive or negative, can be used to make meaningful predictions regarding reproduction and population dynamics in the midge C. tentans.

Community structure and spatial heterogeneity of the deep-sea macrofauna at three contrasting stations in the tropical northeast Atlantic

A study of macrofauna community structure and spatial patterns was undertaken at three deep-sea stations during three EUMELI cruises in the tropical northeast Atlantic Ocean. The benthic response to contrasting regimes of organic carbon supply at the eutrophic (E), mesotrophic (M) and oligotrophic (O) stations (1700 m, 3 100 m and 4700 m depth, respectively) was evaluated through qualitative and quantitative analysis of the composition and structure of benthic macrofauna (> 250 μm) and discussed with regard to the biological and physical conditions. The mean densities of the total macrofauna, dominated by the Polychaeta, Tanaïdacea, Isopoda and Bivalvia, decreased with increasing depth from 5403 ind. m −2 at station E to 231.5 ind. m −2 at station O. From the 16 taxonomic groups represented at the E and M sites, only eight could be sampled at the O site. The density gradient can be related to the decreasing surface production, food supply and hydrographic conditions between the three stations. The comparison of the high densities encountered at station E with other studies underlines the particular feature of this station subjected to intense upwelling activity resulting in high organic carbon input. The patchy distribution of the macrofauna at stations E and M suggests that both physical and biologically-mediated disturbances create environmental heterogeneity favouring the aggregation of organisms. This process occurs at different observation scales. At a large scale, bottom current and upwelling activity induce high densities and faunal aggregations, displaying a degree of density-dependence. At the local scale, the complexity of the food web induces biologically-mediated disturbances, and the activity of major deposit-feeding taxa, like polychaetes, create sediment microhabitats favouring patchy distribution. Faunal patch sizes are variable among the taxa considered. Most are distributed in patches less than 1 m z. Our work contributes to the understanding of how the deep benthic communities are structured, particularly under the influence of environmental conditions in tropical latitudes.

Brent Geese Branta bernicla and Zostera; factors affecting the exploitation of a seasonally declining food resource

Brent Geese Branta bernicla wintering at Lindisfarne, northeastern England, fed almost exclusively on intertidal habitats. Their main food supply was two species of Eelgrass Zostera noltii and Zostera angustifolia. Although abundant when the birds arrived in September, this Zostera was rapidly depleted during the period October‐December. Brent Goose food intake rate declined with the decreasing food supply, and the birds responded by extending the time that they spent feeding. When it was no longer possible to extend the time spent feeding (i.e. they were feeding for all of the time that the food supply was available to them), they moved away from the site. The geese fed extensively at night in order to achieve their daily feeding requirements, especially later in the season. Conversion of daily food intake to energetic intake suggested that there may have been an energetic trigger acting: the geese left the site when they were unable to satisfy their basic energy demand. No evidence was found for direct interference competition between Brent Geese and the other grazer in the system, Wigeon Anas penelope: the two species showed no spatial segregation in their feeding areas at the scale investigated nor any temporal avoidance of each other.

Mathematical model for the size distribution of fish schools

A mechanistic approach to the size distribution of fish schools foraging in patchy environment is presented. Because many schools nomadize in a limited area, interaction between schools occurs so that two of them meet and join, or so that a school splits into smaller ones. This problem is assumed to be described by a Markov process model, where it is asked about the probability that a fish engages in schools of social size N. The stationary distribution of school size which is realized with an overwhelming probability is given by the use of the H-theorem subject to two constraints: the probability distribution is normalized and the population-mean size of school is kept fixed constant. In order to determine the joining or splitting rates of schools, the schooling behavior is mechanistically investigated by examining the function on the foraging for patchily distributed food resources. The most frequently observed size of schools is likely to be regulated by food supply. Faced with a decreasing food supply, the most probable size becomes larger. Moreover, the existence of the optimal school size maximizing the long-term average rate of per capita net energy intake is elucidated. This paper deals with the connection between individual-level performance and patterns at the population level, offering the method to couple the ecologically scaled schooling behavior (i.e., school size distribution) with the environmental condition (i.e., food supply). Data on the size distribution of schools are fitted to the theoretical result fairly well.

Habitat Use and Ecological Correlates of Home Range Size in a Small Cervid: The Roe Deer

1. Summer home range size variation and habitat selection of 35 radio-collared adult female roe deer was studied, using kernel home range estimation and compositional analysis of habitat use. 2. Female roe deer adjust the size of their home range in response to decreasing food supply, and the hypothesis that female roe deer utilize the minimum area that sustain their energy requirement cannot be rejected. 3. Home range size increased with the visibility in the home range (the average distance at which sight is blocked by intervening vegetation). This supports the hypothesis that cover is important in reducing the risk of predation and thereby increasing adult survival. 4. Female roe deer spend more time near habitat edges, supporting the hypothesis that different habitat types contain complementary resources, e.g. food and cover or different nutrients. Simultaneous access to several habitat types did not have any effect on home range size, possibly because variation in heterogeneity between different home ranges was too low. 5. Females without fawns had smaller home ranges, possibly because they only need to sustain their own energetic requirements. 6. The analyses of habitat selection inside each home range showed that the forest types, characterized by high densities of food and low visibility, were preferred, suggesting that habitat use is allocated in proportion to either food or cover or both.

Influence of trawling activity on the breeding ecology of a threatened seabird, Audouin's gull Larus audouinii

The ~nfluence of a trawling moratorium on the breedlng ecology of Audouin's gulls (Larus audouinii Payraudeau) was investigated during 1992 and 1993 in the largest colony of the species in the world (70% of total population), at the Ebro Delta, NE Spain. western Mediterranean. In this colony, Audouin's gull behaves partly as a scavenger following the trawling fleet and exploiting fishing discards. Each year, the trawling moratorium affected different breeding stages of the species: in 1992 it overlapped with pre-laying and laying stages, while in 1993 it affected most of the chick-rearing stage. We examined differences in laying dates, laying interval, clutch and egg slzes, nest desertion during laying, hatching success, hatchling mass and condition, growth rates, chick survival and breeding success. The moratorium greatly affected egg production in 1992, delaying the start of l ay~ng and dramatically decreasing clutch and egg sizes. Intraclutch egg size variation between the 2 years suggests that egg size profiles are outcomes of the interaction between physiological and environmental factors rather than the result of ultimate factors. Nest desertion was much higher in 1992, probably because some females were under a critical body condit~on threshold and they deserted after laying the first egg. Hatching success also decreased significantly during 1992, probably related to changes in the size and the quality of the eggs. Chick growth and survivorship was h ~ g h e r in 1992, when trawler discards were normally available, than in 1993. Trawler discard availability during chick rearing was more important than egg size in determining chick survival. However, differences were not always significant, since In 1993 the n~oratorium did not start until the chicks were 1 wk old, and, further, chicks had h ~ g h e r skeletal size and body condition (in order of Importance) than In 1992. In fact, chicks had similar fledgling condition in both years at the end of the reanng stage. In 1993, the overall breeding success decreased by 4 8 % Nevertheless, gulls' breed~ng performance for the 2 years was much lower than before the establishment of the flrst moratorium In 1991, and the situation suggests that clupeo~ds, the prey on wh.ich Audouin's gull feed, are scarce. It seems that gulls were not able to compensate for the lack of trawler discards during egg production, since the avallablllty of secondary feeding resources was much lower in March and April (pre-laying and laying stages) than in June (chick-rearing stage). Although in long-lived species a decrease in food supply should affect fecundity before affecting adult survival, results confirm the importance of the trawler fleet activity for the conservat~on of this threatened species.

Modeling oyster populations. V. Declining phytoplankton stocks and the population dynamics of American oyster ( Crassostrea virginica) populations

Phytoplankton standing stocks have shown a steady decline in Galveston Bay, Texas over the last 20 years. Phytoplankton provides the primary food resource for oyster populations in Galveston Bay. We used a time-dependent population dynamics model of oyster populations to examine the impact of a decline in phytoplankton stocks on oyster populations. Simulations were run with two different types of mortality: winter mortality, assuming that the oyster fishery is the primary source of mortality; and summer mortality, assuming that predators and disease are the primary source of mortality. All simulations showed the same qualitative trends. Market-size adults disappear from the population in about 4 years, with an approximate 15% decline in food supply. Submarket-size adults maintained an increasing or steady population density for 10–14 years, after which the populations crashed to near extinction in 2–4 years. The proximate cause was a cessation in reproductive activity when food supply ceased to be sufficient to generate a fall spawn, an approximate 60% drop in food from current levels in Galveston Bay. The temporal sequence of mortality affected the outcome very little. The simulations suggest that populations decline rapidly in response to declining food supplies because a minimum food level is required to support a market-size population and a minimal reproductive activity. The simulations suggest that a reduction in market-size individuals is the primary early-warning signal of decreased food supply within the affected population and that this warning signal might easily be mistaken for overfishing. Proper management requires the monitoring of food supply and the use of a mathematical model to assess the importance of observed declines in population abundance. Unfortunately, once the fishery is affected, little time may remain before the termination of spawning and population extinction.

Life-History Strategy of the Herring Gull: Changes in Survival and Fecundity in a Population Subjected to Various Feeding Conditions

The present study compares breeding parameters and adult survival rate in a herring gull colony before and after the closing of a large refuse tip where breeders used to find most of their food. During the first study period (1983-88) food of human origin was abundant and virtually always available. During the second period (1989-90) such food was scarce. The annual adult survival rate was time-dependent. It varied from 0.826 (SE = 0.031) in 1987-88 to 0.975 (SE = 0.022) in 1985-86. The average survival rate calculated for 1983-90 was 0.881 (SE = 0.014). There was no significant difference in adult survival between males and females. The closure of the refuse tip was not followed by a significant decrease in adult survival rate. After the refuse tip was closed, mean clutch size and mean production of young per breeding pair decreased by 6.7% and 49.1%, respectively. Mean adult body weight decreased by 4.6% for males and by 4.7% for females. The proportion of non-breeders among former breeders and the proportion of 3- and 4-year-old individuals among ringed birds did not change after closure of the tip. The results are discussed in terms of the life-history theory, which predicts that in long-lived species a decrease in food supply should affect fecundity before affecting adult survival.

The South Inflamed! The Case of Henry Wirz

To the Editor. — Although I have recently resigned myself to an open season on the Confederacy following the biased public broadcasting series Civil War, I take exception to the comments made by Skolnick 1 in his article. The linking of Major (erroneously called Captain) Henry Wirz, MD, with the German war criminals is inappropriate and uncalled for. These historical facts were ignored: (1) Major Wirz, although a German-trained physician, was a Confederate line infantry officer, not a medical corps officer 2 ; (2) the death rate at Andersonville, Ga, was no worse, and by some accounts better, 3 than that at comparable Union prisoner of war (POW) camps; (3) General Grant's decision to cancel the long-standing prisoner exchanges directly caused the overcrowded conditions; (4) the Yankee blockade and General Sherman's scorched earth policies on his march to the sea caused the decreased food supply, which prisoners and guards shared

Water Flow, Trophic Depletion, and Benthic Macrofauna Impoverishment in a Submarine Cave from the Western Mediterranean

Abstract. Biotic zonation and severe impoverishment of benthic macrofauna are two of the most conspicuous features of submarine caves. The prevailing explanation assumes trophic depletion caused by reduction of water flow. However, no isolation of water was found in the studied Catalan submarine cave, even in the wall microlayer. Fluorescein diffusion was so fast that it was detectable everywhere in the cave already only a few minutes after the injection. The rate of dissolution of plaster spheres was even greater in the cave than in a nearby tunnel – without benthic macrofauna impoverishment – showing a considerable water flow. The oxygen concentration of water in dialysis bags placed at varying distances from the cave walls showed that no wall microlayer gradients were present.Biochemical gradients did not indicate any decrease in food supply. Although photosynthetic pigment concentration generally decreased inside the cave, and although the gradients were not linear but formed different patterns throughout the cave, the BOD5, the POM, the C:N ratio, the [3H]‐thymidine incorporation rate, and the ETS activity were higher in the inner part of the cave. There was an accumulation of detritic material and bacteria in the inner parts that constitute a plausible food supply for benthic macrofauna.If neither water motion nor food supply can be invoked, research into the causes of zonation and disappearence of benthic macrofauna is proposed to be carried out on biotic interactions and behavioural processes.

Models of fish school size in relation to environmental productivity

A simple energy-balance model, relating energetic requirements of fish schools to food production, was used to predict shoal sizes. Lower limits to school size are unlikely to be set by food but rather by predation. Upper limits depend on both food and school behavior, being greater for schools that break up to feed than for schools that remain continuously cohesive. Faced with a decreasing food supply, a school could either break into smaller schools or change behavior, increasing the area available for foraging. The models suggest that environmental productivity needs to be considered when examining fishery statistics such as CPUE (catch per unit effort), where maximum catch may be limited by maximum school size.

The effect of a natural environmental disturbance on maternal investment and pup behavior in the California sea lion

Observed changes in maternal investment due to an environmentally induced decrease in food supply (the 1983 El Nino-Southern Oscillation) are compared witha priori predictions for the California sea lion (Zalophus californianus). Changes in behavior, growth and mortality of off-spring were also examined. Data collected in the first two months postpartum for the years before (PRE), during (EN), and the two years after (POST1 and POST2) the 1983 El Nino indicate that females initiated postpartum feeding trips earlier during the food shortage, and spent more time away on individual feeding trips in both the El Nino year and the year after. Perinatal sex ratios (♀:♂) in the years PRE, EN, POST1 and POST2 were 1:1, 1.4:1, 1.1:1 and 1:1.4, respectively. Fewer copulations were observed during the El Nino year, but this difference was not statistically significant. Pups spent less time suckling in the food shortage year and the year following, but attempted to sneak suckle more. Pups were less active and played on land less in the El Nino and following year. Finally, maternal investment as measured by milk intake of offspring was decreased, pups grew more slowly, and suffered increased mortality during the food shortage year. Despite expected sex differences in maternal investment and pup behavior in response to food shortage, there were no sex-biased differences in response in either females or pups. As expected, the food shortage did not affect adult males since they migrate north during the non-breeding season where the environmental perturbation was less severe.

Breeding Ecology of the Hawaii Common Amakihi

The ecology and breeding biology of the Common Amakihi (Hemignathus virens) was studied on Mauna Kea, Hawaii, from 1970 through 1981. Common Amakihi retained mates for more than one season and returned each year to the same area to breed. There was an excess of unmated males in the population. First-year birds were rarely successful in their initial breeding attempt. The species had a protracted breeding season, with nests found in every month of the year except August through October. However, the most intensive breeding occurred from March to May, that period of greatest mamane (Sophora chrysophylla) flowering. Ritualized courtship in the Common Amakihi included high altitude and low altitude chases. Territories encompassed the nest site and all food resources, and was a fixed location that often had the same boundaries in succeeding years. The size and location of territories were related to available food resources. Nests were statant, open cupped, with mamane trees the preferred nesting substrate. Clutch size averaged 2.5 eggs and varied between years such that, in a year of low food availability, birds with smaller clutch sizes fledged more young than did those with larger clutches. Incubation period was 14 days and clutches hatched asynchronously. Difference in nestling sizes resulted in brood reduction through elimination of the smallest individual in years of decreased food supply. The nestling period averaged 17 days and young usually fledged synchronously. Both parents fed the young but only the female incubated and brooded. Based on 150 nests with complete records, hatching success was 53.5%, fledging success was 64.9%, and overall reproductive success was 34.7%. The major mortality factor during the breeding cycle was nest desertion by the adults. There were six major factors which influenced productivity on Mauna Kea. The two most important were length of the breeding season and clutch size. Other factors were territoriality, hatching sequence, nestling growth rates, and nestling mortality.