Mean Brood Size Research Articles

LIFE HISTORY CHARACTERISTICS OF ELACHERTUS CACOECIAE (HYMENOPTERA: EULOPHIDAE), AN ECTOPARASITOID OF SPRUCE BUDWOR LARVAE, CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE)

AbstractWe carried out a 2-year study to elucidate the biology of the gregarious, idiobiont ectoparasitoid Elachertus cacoeciae (Howard) by placing (implanting) laboratory-reared spruce budworm larvae [Choristoneura fumiferana (Clemens)] on current-year balsam fir (Abies balsamea L.) shoots in the field, simulating low (endemic) densities of the budworm. Spring female E. cacoeciae attacked fourth-, fifth-, and sixth-instar budworm larvae, beginning near the predicted peak of the fourth instar and ending about 10–12 days after the predicted peak of the pupal stage of the wild budworm population. The mean (±SE) brood size of spring females was 2.9 ± 0.3 E. cacoeciae pupae per host. The proportion of females increased during the season, with many broods consisting of 100% females late in the season. In 1994 and 1995, the mean proportion of females was 0.74 ± 0.05 and 0.79 ± 0.05, respectively. In the laboratory, development time from eggs to adults was approximately 20 days at 20.6 °C. Adult males provided with honey water lived 43.6 ± 3.2 days, whereas females provided with hosts and honey water lived 90.1 ± 6.6 days. Spring females had a pre-oviposition period of 11.5 ± 1.3 days, resulting in a generation time (egg to egg) of ~31 days. The oviposition period lasted 76.3 ± 7.7 days during which time spring females parasitized 19.2 ± 1.9 hosts, and produced a clutch size of 4.9 ± 0.4 eggs per host, for a lifetime fecundity of 96.8 ± 14.7 eggs. The post-oviposition period was 18.5 ± 3.7 days. Throughout their lifetime, spring females host fed only (host feeding without oviposition) on an additional 9.3 ± 1.9 hosts. Approximately 2% of pupae developing from spring females overwintered, whereas approximately 95% of pupae developing from summer females overwintered. Laboratory results for summer females suggest that they may be adapted to parasitizing alternate host(s) rather than spruce budworm.

Brood Sizes of Sympatric American Black Ducks and Mallards in Maine

The long-term decline of the American black duck (Anas rubripes) population has been attributed to lower productivity of black ducks that might have been excluded from fertile agricultural wetlands by mallards (Anas platyrhynchos). We monitored broods on 53 wetlands in 1993 and on 58 wetlands in 1994 to determine mean brood sizes of black ducks and mallards in forested and agricultural landscapes. Study wetlands were moderately to highly fertile. We monitored 94 black duck broods each year and 46 (1993) and 52 (1994) mallard broods until they reached Class IIC-III (near fledging). No differences existed (P = 0.71) in mean brood size between black ducks (1993: 3.95 ± 0.23; 1994: 4.59 ± 0.24) and mallards (1993: 3.96 ± 0.35; 1994: 5.00 ± 0.43) either year. Brood size for species, however, was different between years (P = 0.014) and among wetland sites (P = 0.001). Mean sizes of broods were larger (P < 0.05) on 2 large impoundment complexes (Lake Josephine and Lake Christina) compared with brood sizes on other wetlands in forested or agricultural landscapes. No differences (P ≥ 0.41) existed between mean Class IIc-III brood sizes of black ducks and mallards, whether species were alone or together on wetlands. Our data document that mallard productivity is similar to that of black ducks where they breed sympatrically in Maine.

Reproductive biology of the mosquitofish in a permanent natural lagoon in south-west Spain: two tactics for one species

Introduced Gambusia holbrooki in a natural lagoon of southern Spain consisted of two age groups: 1992 cohort, 7-11 months old and 1993 cohort, <4 months old. In the 1992 cohort, females grew even during the gestation period at about 0.30 mm day-1. In the 1993 cohort, females displayed a high growth rate (0.55 mm day-1) and reached reproductive size in a few weeks, but stopped growing when they matured. All the 1992 cohort reproduced from mid-May to mid-June, but only 50% of the 1993 cohort reproduced, from mid-August to mid-September. Reproducing females were significantly larger in the 1992 cohort (39.8 mm) than in the 1993 one (34.8 mm). The largest 1992 females cohort had reproduced previously; the 1993 cohort had not. The mean dry weight of intra-ovarian embryos decreased to a minimum immediately before birth. These metabolic costs represented 29.8 and 31.4% of the initial weights of the 1992 and 1993 embryos, respectively. Mean dry weight of full-term embryo was significantly higher in the 1992 cohort (0.80+/-0.129 mg; 95% CL) than in the 1993 one (0.70+/-0.086 mg; 95% CL). With more females in 1992, cohort fecundity was considerably higher (number of embryos=7151; 63%) than in the 1993 (4193; 37%) cohort. The population completed two generations each year (spring and summer). The spring stock grew slower than the summer one but continued to grow during the gestation period, reaching larger final lengths, with more synchronous reproduction and clearer evidence of a second reproductive event. Each reproductive stock displayed its own life-history characteristics, with significant differences between mean length of reproducing females, growth rate, mean brood size, offspring size, standard fecundity and minimum length at reproduction.

The Effect of Agricultural Landscape Structure on Food Resources and Survival of Grey Partridge Perdix Perdix Chicks in Poland

1. The relationships between the agricultural landscape structure, as a function of arable field size and the occurrence of permanent cover, and the abundance of insect food and partridge chick survival were studied in two areas of Poland. One area had small and large fields (Czempin) and the other had only small fields (Kutno). Brood size was used as an index of chick survival and the number of plant bugs (Heteroptera) as an index of chick food resources. 2. The number of plant bugs in cereals increased with permanent cover in Czempin, but no relationship was found in Kutno where there was more permanent cover and smaller field sizes. 3. The average number of plant bugs was higher in small arable fields than in large fields. However, the number of insects near permanent cover in small and large arable fields did not differ. 4. The mean brood size of partridges in small arable fields increased with permanent cover in Czempin, but not in Kutno. No differences were found in mean brood size between small and large arable fields. 5. Simplifying the agricultural landscape structure could be an important feature of agricultural intensification that results in lower partridge chick survival.

Seasonal Decline in Body Size of Coot Chicks

I investigated the seasonal variation in growth rates among the semi-precocial chicks of European Coots Fulica atra. Mean body size and nutritional condition at four weeks of age showed a distinct seasonal decline among first broods, whereas variation in growth was independent of hatching date among later broods. Body dimensions differed between years, but there was no significant between-year variation in the seasonal patterns in chick growth. The seasonal pattern in mean body size was not explained by differences in mean egg mass, brood size or parental age between early and late breeding pairs. Independently of hatching date, chick body size was positively related to egg mass and negatively to brood size one week after hatching. To ascertain whether the seasonal decline in chick growth among first broods was due to a difference in the quality of early and late pairs (parental quality hypothesis), the brood care period of individual pairs was experimentally advanced or delayed by exchanging clutches that differed in laying date. In the first half of the season, the mean body size and nutritional condition of broods of experimental pairs were associated with the original hatching date, and not with the assigned actual (advanced or delayed) hatching date. Hence, the higher growth rate in the earliest broods was consistent with the parental quality hypothesis. In the second half of the season the mean body size and nutritional condition of broods fostered by experimentally advanced or delayed pairs were associated with the actual hatching date, and not with the original one. Thus, the mean body size and condition of chicks were causally related to hatching date in the second half of the season, either through a hatching date-linked deterioration of the environmental conditions for chick growth (date hypothesis) or through a decline in the quality of chicks with progressive hatching date (chick quality hypothesis). Analysis of individual variation in body size among chicks which were sexed upon recapture as adults, revealed a seasonal decline only among males. Body dimensions of female chicks were independent of hatching date. Finally, chicks of either sex that grew poorly were significantly smaller as adults. Therefore, variation in juvenile growth may represent a major factor in determining the reproductive value of coot chicks, as breeding success may depend on phenotypic differences in adult size.

Interactive Effects of Prey and Weather on Golden Eagle Reproduction

1. The reproduction of the golden eagle Aquila chrysaetos was studied in southwestern Idaho for 23 years, and the relationship between eagle reproduction and jackrabbit Lepus californicus abundance, weather factors, and their interactions, was modelled using general linear models. Backward elimination procedures were used to arrive at parsimonious models. 2. The number of golden eagle pairs occupying nesting territories each year showed a significant decline through time that was unrelated to either annual rabbit abundance or winter severity. However, eagle hatching dates were significantly related to both winter severity and jackrabbit abundance. Eagles hatched earlier when jackrabbits were abundant, and they hatched later after severe winters. 3. Jackrabbit abundance influenced the proportion of pairs that laid eggs, the proportion of pairs that were successful, mean brood size at fledging, and the number of young fledged per pair. Weather interacted with prey to influence eagle reproductive rates. 4. Both jackrabbit abundance and winter severity were important in predicting the percentage of eagle pairs that laid eggs. Percentage laying was related positively to jackrabbit abundance and inversely related to winter severity. 5. The variables most useful in predicting percentage of laying pairs successful were rabbit abundance and the number of extremely hot days during brood-rearing. The number of hot days and rabbit abundance were also significant in a model predicting eagle brood size at fledging. Both success and brood size were positively related to jackrabbit abundance and inversely related to the frequency of hot days in spring. 6. Eagle reproduction was limited by rabbit abundance during approximately two-thirds of the years studied. Weather influenced how severely eagle reproduction declined in those years. 7. This study demonstrates that prey and weather can interact to limit a large raptor population's productivity. Smaller raptors could be affected more strongly, especially in colder or wetter climates.

Breeding success, dispersal, and long-term changes in a population of Eagle Owls Bubo bubo in southeastern Sweden 1952–1996

In 1950 when the Eagle Owl became legally protected in Sweden, the species was nearly extinct in most parts of the country and survived only with a small population in the southeastern part of the country, along the Baltic Sea coast. This population has been studied in 1952–1996. Recoveries of birds ringed in the study area demonstrated that dispersal was limited; post-fledging dispersal was on average 56.8 km in the first year of life. In birds older than one year the mean distance from the hatching site to the site of recovery was 47.7 km. The mean brood size in successful nests was 1.47 young. However, the mean reproductive success calculated for all occupied territories was only 0.68 young per pair and year. Among all pairs, 43.7% bred successfully and 24.7% failed. Thus, each year 31.6% of the pairs stayed in the territory without breeding. For an extended part of this long term study, reproduction seems to have been just enough to maintain a stable population size in the study area. Only in the years 1986–90, there seemed to be a surplus of young produced in the study population resulting in new breeding pairs, predominantly outside the old study area. From a national project with captive breeding, 2,759 young Eagle Owls have been released in nearly all parts of Sweden. Around 1982, the number of pairs originating from the released birds was in equilibrium with the original "wild" population, and in 1995 the released birds and their descendants were about twice as many. In recent years probably many pairs are of mixed origin, and the mixing of the two populations is likely to increase in the future. In total, there were about 400 territories occupied by Eagle Owls in Sweden in 1996.

Long-term reproductive performance in White-fronted GeeseAnser a. albifronsand Tundra Bean GeeseA. fabalis rossicuswintering in Zeeland (The Netherlands)

The reproductive performance of White-fronted Geese and Tundra Bean Geese was surveyed during 1964/65 to 1994/95 in southern Zeeland (the Netherlands). The proportion of first-year birds was higher on average in the White-front than in the Tundra Bean Goose (29 ± 10% and 25 ± 5%) and mean brood-size was also higher (2.5 ± 0.3 versus 2.1 ± 0.2). During the first five years of the survey, more than 15% of broods in both species were single-parent, this proportion dropped to 5–10% in the course of the 1970s. No trend in time in reproductive parameters of either species was found. The proportion of first-year birds was significantly correlated with mean brood-size in both species. In the White-fronted Goose both parameters show a pattern of poor breeding every three years and the proportion of first-year birds is strongly correlated with those of the Dark-bellied Brent Goose. No cyclical variations were found in the Tundra Bean Goose, perhaps because its breeding range is more southerly than that of the White...

Chronic Toxicity of Fenitrothion to an Algae (Nannochloris oculata), a Rotifer (Brachionus calyciflorus), and the Cladoceran (Daphnia magna)

Chronic toxicity studies were conducted with an algae (Nannochloris oculata), a rotifer (Brachionus calyciflorus), and a cladoceran (Daphnia magna) to determine their relative sensitivities to the organophosphorus insecticide fenitrothion. The cladoceranD. magnawas the most sensitive of the three species. The no observed effect concentrations (NOECs) for the study with the algae (1.0 mg/liter) and for the rotifer (1.0 mg/liter) were higher than the NOEC (0.009 μg/liter) and the LC50of 24 hr (0.067 μg/liter) forD. magna. Most of the algal populations were not initially affected by exposure to fenitrothion. Pesticide concentrations higher than 1.0 mg/liter significantly reduced algal densities after 72 hr exposure. The effects of chronic exposure of the rotiferB. calyciflorusto fenitrothion were evaluated using some demographic parameters: intrinsic rate of natural increase (r), generation time, net reproductive rate, and life expectancy. All the parameters studied decreased with increasing toxicant concentrations. The parameters used to determine the effect of the pesticide onD. magnareproduction were mean total young per female, mean brood size, mean time to first reproduction, andr. Therand the rest of the studied parameters were affected at 0.011-μg/liter and higher fenitrothion concentrations. Growth, as measured by body length, was only depressed significantly at 0.011 μg/liter pesticide.

Habitat-related variation in movements and fledging success of American black duck broods in northeastern Nova Scotia

Female American black ducks (Anas rubripes) are known to move their broods from low- to high-nutrient rearing sites. We studied the extent of brood movement and fledging success in a northeastern Nova Scotia watershed. Annually, about half the broods moved either overland or along three rivers from small, widely dispersed oligotrophic–mesotrophic wetlands to a large hypertrophic tidal marsh. Mean brood size at fledging was 3.50 in the tidal marsh but 7.05 at the dispersed freshwater wetlands. Females that remained at dispersed sites fledged more ducklings than females that moved to the marsh. Attrition occurred predominantly in the marsh or in transit. Females fledged fewer young when they raised broods at the marsh than when the same females raised broods at inland sites. Females were as successful at nutrient-poor sites as at nutrient-rich sites. The study suggests that concentrating birds in nutrient-rich sites may be counterproductive in terms of female reproductive fitness and population recruitment.

Phenology and breeding success of Red-necked NightjarCaprimulgus ruficollis in southern Spain

Data of 37 Red-necked Nightjar nests were collected during four seasons in a locality of southern Spain. Breeding season elapsed from late May to early August with two clutches laid. Mean brood size was 1.59 (N=29) for successful nests and 1.24 (N=37) for all nests. Nest failure was due to agricultural work and predation byLacerta lepida. The percentage of eggs that successfully became a fledgeling was significantly higher for cltuches found in May than in June or July. The median laying and hatching dates were 7 and 19 June respectively. Incubation period recorded was 17 days. Hatching date, but not laying date, significantly varied among years. These results are compared with those available for the European Nightjar C.europaeus.

Fecundity and Seasonal Changes in Reproductive Output of Females of the Gravel Beach Amphipod, Pectenogammarus Planicrurus

Pectenogammarus planicrurus Reid (Crustacea: Amphipoda) is an inhabitant of unstable gravel beaches. The reproductive output of females of this species was studied at Aberystwyth, on the west coast of Wales. There was marked seasonal variation in the size of eggs: the mean volume of eggs at an early stage of embryonic development ranged from 0·023 mm3 in summer to 0·030 mm3 in winter. Egg size was negatively related to brood size, but seasonal variation in brood size was greater than could be accounted for by egg size alone. Mean brood size ranged from 1·4 eggs in winter to 5·9 eggs in summer. Brood size was also strongly related to female body size, ranging up to 14 eggs in a large female. These findings are discussed in relation to adaptation to interstitial living in coarse intertidal gravels. A model of seasonal variation in reproductive output is suggested in which the importance of point reproductive output is related to the probability of females surviving to produce subsequent broods.

State-Dependent Life Histories, Mountford's Hypothesis, and the Evolution of Brood Size

1. Mountford's cliff-edge hypothesis states that asymmetrically low survivorship in large broods can account for the common observation that mean brood size is less than the most productive size. A graphical model demonstrates how state-dependent life histories can explain Mountford's hypothesis. The model is based on the optimal allocation of parental resources to reproduction. It assumes that the optimum brood size depends upon the state of each phenotype in the population. 2. Variability among individuals will cause some to produce either smaller or larger broods than their optimum. Juvenile survival is expected to decline with increases in brood size beyond the parental optimum. Juvenile survival from large broods produced by low-quality parents will be exceptionally low, thereby generating Mountford's cliff-edge effect. 3. I tested the model with field data on the success of litters produced by small and large females of the white-footed mouse. The data, in this initial test of state-dependent life history theory, were consistent with the state-dependent explanation. Small females that produced large litters had significantly lower recruitment from those litters than did larger females that produced litters of the same size. 4. Interactions among litter size, juvenile survival, maternal body size and the timing of reproduction document that detailed natural history will be an essential feature in future tests of state-dependent theories.

Cotesia orobenae (Hymenoptera: Braconidae), a Gregarious Endoparasitoid of Evergestis rimosalis (Lepidoptera: Pyralidae), and Hyperparasitoids in Virginia Brassica Crops

Abstract Cotesia orobenae Forbes (Hymenoptera: Braconidae) is a gregarious endoparasitoid of the cross-striped cabbageworm (Evergestis rimosalis Guenee) (Lepidoptera: Pyralidae), a minor pest of Brassica crops in Virginia. Cocoons of C. orobenae were collected, weekly, from field plots of broccoli and cabbage crops in Whitethorne, Montgomery County (VA) during 1989 and 1990. Counts were also made of the eggs and larvae of E. rimosalis to determine the pest′s seasonality. In January 1991, C. orobenae cocoons were collected from the held plots to see if C. orobenae overwinters within cocoons. In May 1993, trap plants bearing E. rimosalis larvae were placed among the field plants weekly to determine if C. orobenae adults are present and ovipositing early in the season. Field counts of E. rimosalis eggs and larvae in 1990 indicated the occurrence of three generations off. rimosalis from June to October, but parasitism of larvae on trap plants by C. orobenae in May 1993 suggested that the parasitoid is present in mid-May. C. orobenae oviposits in first through third instar E. rimosalis and the resulting larvae feed internally on the developing host, exit the fourth (last) instar host, and spin cocoons in a loose mass. Mean brood size of 118 C. orobenae field-collected cocoon masses was 9.2 ± 4.4 cocoons per mass. Out of 1085 cocoons, adult C. orobenae emerged from 77%, hyperparasitoids emerged from 7%, and nothing emerged from 16%. Females accounted for 73% of the emerging C. orobenae adults. Data from field-collected cocoons suggest that C. orobenae enter diapause in late September and overwinter in cocoons. Six pupal hyperparasitoids were recovered: Isdromas lycaenae (Howard) (Ichneumonidae); Conura (=Spilochalcis) torvina (Cresson) and Conura (=Spilochalcis) albifrons (Walsh) (Chalcididae); Hypopteromalus tabacum (Fitch), Catolaccus cyanoideus Burks, and Trichomalopsis viridescens (Walsh) (Pteromalidae).

Reproductive Cycles and Temporal Variation in Fecundity in the Black Swamp Snake, Seminatrix pygaea

-We studied the reproductive ecology of female black swamp snakes (Seminatrix pygaea) at Ellenton Bay, South Carolina, from 1983-1987. Females followed a Type I reproductive cycle, with rapid follicular growth in the spring, ovulation in June, and parturition in early August. There was no evidence of multiple clutches but most females were reproductively active in all years. Mean brood size for 70 females was 8.0 (range = 4-15) offspring, and brood size was positively related to maternal body size. Variability in reproductive traits was low. Despite a severe decrease in food availability in the last year of the study, we found no significant variation in mean brood size or proportion of females gravid among years, in contrast to studies on most other species of snakes followed for more than 2 yr. However, the relationship between brood size and female size differed among years.

Chronic toxicity of diazinon todaphnia magna:Effects on survival, reproduction and growth

The sublethal effect of 0.15, 0.18, 0.22, 0.25 and 0.30 μg/L diazinon on the survival, reproduction and growth of D. magna was monitored for 21 days. Neonates (≤ 24 h) were obtained from the stock cultures and raised individually in 50 mL glass beakers. All daphnids were transfered every other day to a new beaker containing fresh medium, food and the appropriate pesticide concentration. The animals were maintained in an environmental chamber at 22±1°C on a 12L: 12D photoperiod and were fed daily on 5 x 105 cell/mL of the green algae Nannochloris oculata. The parameters used to determine the effect of the pesticide on reproduction were: mean total young per female, mean brood size, mean number of broods, mean time to first reproduction and intrinsic rate of natural increase “r”. Growth of surviving adults was determinated after 21 days of exposure. The maximun acceptable toxicant concentration (MATC) was also calculated. Survival was affected with 0.18, 0.25 and 0.30 μg/L diazinon. All concentrations cause...

Recruitment in Rocky Mountain Greater Sandhill Cranes and Comparison with Other Crane Populations

The sandhill crane (Grus canadensis) has the lowest known recruitment (% juv in fall and winter of any avian species hunted in North America. Long-term recruitment data provide insight into a population's productivity, ability to support harvest, and responses to management programs. During 1972-92, we annually collected age ratio (n = 191,968) and brood size (n = 12,239) data for greater sandhill cranes (G. c. tabida [greaters]) of the Rocky Mountain Population (RMP) at their migration stopover in the San Luis Valley, Colorado (fall), and at sites in New Mexico (winter) and southeastern Arizona (winter). We collected similar data (1987-92) for lesser sandhill cranes (G. c. canadensis [lessers]) from the Midcontinent Population (MCP) wintering in flocks mixed with RMP cranes, and for greaters of the Lower Colorado River Valley Population (LCRVP) wintering in western Arizona (1973-75 and 1989-92). Annual recruitment in the RMP averaged 8.1% (SE = 0.6) in fall and 8.0% (SE = 0.5) in winter over 21 years; mean brood size was 1.25 (SE = 0.02) in fall and 1.23 (SE = 0.02) in winter. In years with higher percent juveniles, more pairs fledged multiple young (P < 0.01); second and rarely third chicks in broods composed 20% of RMP recruitment. Recruitment and brood size had a downward trend (P < 0.01) over 21 years. During 1986-92, recruitment and brood size were below average (P < 0.01), apparently due to drought in breeding areas. We estimated survival rates of RMP cranes to be 0.95 during 1972-85, 0.94 during 1985-90, and 0.91 during 1990-92. Recruitment, survival estimates, and count data during 1985-92 suggest that the RMP is stable at 20,000-21,500 or declining slightly and cannot sustain increased harvest. Recruitment in MCP lessers averaged 11.2% (SE = 0.34) and mean brood size was 1.14 (SE = 0.02). Mean recruitment in LCRVP greaters was 4.8% (SE = 0.93), and mean brood size was 1.14 (SE = 0.028). Mean recruitment in most other North American crane populations was 5-14%. The whooping crane (G. americana) has the highest long-term (55 yr) recruitment (13.9%) of any North American crane population. Recruitment data alone cannot be used to estimate rate of increase and are difficult to interpret without additional demographic information. However, perennially low recruitment (≤ 5-6%) approximates the lowest documented mortality rates in any North American crane population, and should be a cause for concern, particularly in hunted populations. Management of crane populations can be improved by annually gathering data on recruitment, population size, and hunter harvest, and by obtaining survival estimates from long-term studies

The breeding biology of the DipperCinclus cinclusin south-west Ireland

The breeding biology of Irish Dippers was studied over 12 years. A total of 501 nests was located, mostly at artificial sites, notably bridges. Irish Dippers start breeding earlier, lay fewer eggs, fledge fewer young and have fewer second broods than most other populations. The mean clutch size was 4.16 (±se 0.03) and the mean brood size at fledging was 3.48 (±¸se 0.05) per successful pair. The breeding biology is compared with other populations and some differences are highlighted.

Evaluation of agro-industrial wastes as diets for culture of the fairy shrimpStreptocephalus proboscideus (Frauenfeld, 1873) (Crustacea:Branchiopoda:Anostraca)

Two micronized waste products were evaluated in a closed recirculation system for their suitability to replace a costly diet of live algae in the culture of the Sudanese fairy shrimp, Streptocephalus proboscideus. The test population was kept at a density of 50 individuals l−1 (sex ratio: 1/1). An agricultural waste product (YM20; mixture of pea and corn), and an industrial waste product (POME; Palm Oil Mill Effluent) were fed at two regimes: 0.1 and 0.2 mg DW animal−1 h−1. The microalga Selenastrum capricornutum, used as a reference diet at a density of 2.0±0.82 × 105 cells ml−1, proved adequate in preliminary screening experiments. The effect of the diets and feeding regimes on selected biological variables and water quality were followed by weekly observations and measurements. Results in terms of growth (= increase in length), cyst production, and mortality were more successful when animals were supplied high densities of YM20 than in all other treatments: mean brood size was 155±6 cysts with a maximum of 266. Length after 6 weeks was about 2 cm while this ranged between 1.4–1.7 cm for the other treatments. Weekly mortality rate was comparable under high food conditions. Mortality rate gradually increased from 5% in the first week to 15% in the last week. Water quality, especially nitrite concentration (measured as NO2-N), was slightly better in the dry food fed than in the algae fed cultures. Present results are promising for large-scale culturing of S. proboscideus in a cost-effective way by making use of agro-industrial waste products.

Survival of Juvenile Black Brant during Brood Rearing

Survival of young is an important and poorly understood component of waterfowl productivity. We estimated survival of black brant (Branta bernicla nigricans) goslings during summers 1987-89 on the Yukon-Kuskokwim Delta, Alaska, to determine timing and magnitude of gosling mortality and to compare methods of estimating gosling survival. Eighty-two percent of radio-tagged adult females (n = 61) fledged ≥1 gosling (brood success). We estimated survival of goslings within broods by 3 methods: (1) changes in mean brood size through time, (2) observation of goslings associated with marked adults, and (3) age ratios of brant captured in banding drives. Estimates of gosling survival within successful broods averaged 81% and ranged from 66 to 92%. Combining brood success and gosling survival within successful broods yielded estimates of overall gosling survival that averaged 68%, ranging from 79% in 1987 to 56% in 1989. Eighty-two percent of gosling mortality occurred in the first 15 days. Estimates of survival on the basis of age ratios of birds captured in banding drives are biased low. Our estimates of average gosling survival are higher than reported for other species of geese.