Seasonal Fecundity Research Articles

Impact of Brood Parasitism on Nest Survival Parameters and Seasonal Fecundity of Six Songbird Species in Southeastern Old-Field Habitat

Abstract We monitored 259 nests of six Brown-headed Cowbird (Molothrus ater) hosts within old-field habitat on James Island, South Carolina during the 1997 and 1998 breeding seasons to determine the effect of parasitism on three nest-survival parameters (clutch size, hatching rate, and number of fledglings). We determined daily predation and parasitism rates, and probability of nest abandonment after parasitism to derive an estimate of seasonal fecundity. Clutch size of parasitized nests was reduced in four host species. Brood parasitism did not affect hatching rate in any species, and reduced the number of fledglings from only Blue Grosbeak (Guiraca caerulea) nests. Despite brood reduction during the nesting cycle, cowbird parasitism had little impact on seasonal fecundity of these host species because of low parasitism intensity, double-brooding behavior, and hosts' ability to raise their own young with cowbird young.

Demography of Bell's Vireos in Missouri Grassland-Shrub Habitats

Abstract Numbers of Bell's Vireos (Vireo bellii) have declined throughout much of the breeding range in recent years, yet little information exists to determine factors that are causing these declines. We studied Bell's Vireos nesting in grassland-shrub habitats at two study areas in central Missouri to determine reproductive performance, survival, and population growth potential. Birds were color banded and observed during the breeding seasons of 1996, 1997, and 1998 to determine seasonal fecundity. We monitored 124 breeding pairs (127 pair years) and 213 nests. Density declined from 1.00 to 0.80 territories per 10 ha at the first site and increased from 1.11 to 1.33 at the second site during the study. Mean nesting success was 31 ± SE of 0.03% overall and ranged from 13 to 42% among years and study areas; 57% of the pairs fledged at least one young. Low annual production was a function of high rates of nest predation (41% of all nests observed, accounting for 44 to 78% of daily nest mortality annually) and nest parasitism by Brown-headed Cowbirds (Molothrus ater; 29% of nests observed, 17 to 37% of daily nest mortality annually). Mean seasonal fecundity was 1.60 young fledged per pair per year (range 1.00 to 1.79). Annual survival of adults was 61 ± 0.04% and was higher than previously reported. We used our estimates of seasonal fecundity and annual survival of adults to determine the finite rate of increase (λ) for our study population. Our study areas seemingly comprised sink habitats (λ = 0.85). Thus, the vireos on our study areas likely were limited by low reproductive success. Population declines also may be caused by habitat loss, which highlights the need for investigation of historical and current rates of loss of grassland-shrub habitat.

VALIDATING THE ASSUMPTIONS OF THE MAYFIELD METHOD

We tested the assumptions of the Mayfield method (Mayfield 1975) using 416 Wood Thrush (Hylocichla mustelina) nests monitored from 1993–1997 in the Great Smoky Mountains National Park. We tested for differences in nest survival throughout the breeding season and throughout the nesting cycle. We compared the Mayfield cumulative survival curve with a modified version of the Kaplan-Meier with staggered entry. In addition, we compared the group of nests found during nest initiation with those found later in the nesting cycle. There was no evidence nest survival varied through the breeding season or with different stages of the nesting cycle. Furthermore, the Kaplan-Meier survival curve agreed with the Mayfield calculation. We found no evidence of heterogeneity. Validation of Mayfield assumptions is important because the method is widely used, allows for statistical comparisons, and is critical for estimating seasonal fecundity in bird populations.

Comparative Seasonal Fecundity of Four Neotropical Migrants in Middle Appalachia

Abstract We estimated daily rates of nest predation and Brown-headed Cowbird (Molothrus ater) parasitism as well as nesting success for the Red-eyed Vireo (Vireo olivaceus), Blue-headed Vireo (V. solitarius alticola), Wood Thrush (Hylocichla mustelina), and Worm-eating Warbler (Helmitheros vermivorus) at two study sites in the middle Appalachian mountains from 1995–1998. These daily rates were then used in combination with species-specific life history parameters to estimate seasonal fecundity. Although daily predation rates were similar across species and sites, parasitism rates and nesting success differed within species between sites and among species within a site. The vireos generally experienced the highest rates of parasitism and subsequently the lowest estimates of seasonal fecundity. However, differences in parasitism and nesting success were not always an accurate predictor of seasonal fecundity. Despite significantly different estimates of nesting success, the Red-eyed Vireo and Blue-headed Vireo had similar estimates of seasonal fecundity. In contrast, estimates of nesting success for the Worm-eating Warbler and Wood Thrush were similar yet there were differences in seasonal fecundity. Life history attributes such as season length, ability to produce additional broods, and ability to raise a host young with a cowbird young were important in determining seasonal fecundity among species. We show the importance of including multiple species within a study framework and illustrate how predation and parasitism differentially affect these species with respect to seasonal fecundity.

Comparative Seasonal Fecundity of Four Neotropical Migrants in Middle Appalachia

Comparative Seasonal Fecundity of Four Neotropical Migrants in Middle Appalachia

COMPARATIVE SEASONAL FECUNDITY OF FOUR NEOTROPICAL MIGRANTS IN MIDDLE APPALACHIA

We estimated daily rates of nest predation and Brown-headed Cowbird (Molothrus ater) parasitism as well as nesting success for the Red-eyed Vireo (Vireo olivaceus), Blue-headed Vireo (V. solitarius alticola), Wood Thrush (Hylocichla mustelina), and Worm-eating Warbler (Helmitheros vermivorus) at two study sites in the middle Appalachian mountains from 1995–1998. These daily rates were then used in combination with species-specific life history parameters to estimate seasonal fecundity. Although daily predation rates were similar across species and sites, parasitism rates and nesting success differed within species between sites and among species within a site. The vireos generally experienced the highest rates of parasitism and subsequently the lowest estimates of seasonal fecundity. However, differences in parasitism and nesting success were not always an accurate predictor of seasonal fecundity. Despite significantly different estimates of nesting success, the Red-eyed Vireo and Blue-headed Vireo had similar estimates of seasonal fecundity. In contrast, estimates of nesting success for the Worm-eating Warbler and Wood Thrush were similar yet there were differences in seasonal fecundity. Life history attributes such as season length, ability to produce additional broods, and ability to raise a host young with a cowbird young were important in determining seasonal fecundity among species. We show the importance of including multiple species within a study framework and illustrate how predation and parasitism differentially affect these species with respect to seasonal fecundity.

IMPACT OF BROOD PARASITISM ON NEST SURVIVAL PARAMETERS AND SEASONAL FECUNDITY OF SIX SONGBIRD SPECIES IN SOUTHEASTERN OLD-FIELD HABITAT

Abstract We monitored 259 nests of six Brown-headed Cowbird (Molothrus ater) hosts within old-field habitat on James Island, South Carolina during the 1997 and 1998 breeding seasons to determine the effect of parasitism on three nest-survival parameters (clutch size, hatching rate, and number of fledglings). We determined daily predation and parasitism rates, and probability of nest abandonment after parasitism to derive an estimate of seasonal fecundity. Clutch size of parasitized nests was reduced in four host species. Brood parasitism did not affect hatching rate in any species, and reduced the number of fledglings from only Blue Grosbeak (Guiraca caerulea) nests. Despite brood reduction during the nesting cycle, cowbird parasitism had little impact on seasonal fecundity of these host species because of low parasitism intensity, double-brooding behavior, and hosts' ability to raise their own young with cowbird young.

Reproductive Success of Wood Thrushes in Forest Fragments in Northern Indiana

AbstractI monitored 278 Wood Thrush (Hylocichla mustelina) nests in 14 forest fragments (range 7 to 500 ha) in northern Indiana to explore patterns of brood parasitism by Brown-headed Cowbirds (Molothrus ater), nest predation, and reproductive success. Density of thrushes was negatively related to area of forest fragments. Cowbirds were common throughout the landscape, but I found no relationship between their abundance and forest area. Overall, 90% of the thrush nests were parasitized by cowbirds (x̄ = 2.4 cowbird eggs per nest). The number of cowbird eggs per thrush nest was not related to forest area, abundance of host species, or distance to a forest edge but was positively related to thrush abundance. Nest predation rates averaged 58% and were lower than those reported in much of neighboring Illinois but also were unrelated to forest area and distance to a forest edge. The combination of cowbird parasitism and nest predation resulted in relatively low reproductive success (x̄ = 0.6 thrush fledglings per nesting attempt). I estimated that Wood Thrushes in northern Indiana made an average of three nesting attempts per breeding season (based on 17 color-marked females) and had relatively low seasonal fecundity (x̄ = 0.9 female fledglings per adult female per season). Nonetheless, considerable annual variation in seasonal fecundity suggested that some sites exceeded the source-sink threshold in some years. Regardless, the overall landscape appeared to be part of a regional sink for Wood Thrushes, although its negative influence on regional demography was not as severe as elsewhere in the midwestern United States. The poor demographic balance in much of the agriculturally dominated Midwest suggests that conservation efforts for Wood Thrushes and other Nearctic-Neotropical migrants should be directed at preserving and enhancing possible source habitats in regions where parasitism by cowbirds and nest predation are reduced.

REPRODUCTIVE SUCCESS OF WOOD THRUSHES IN FOREST FRAGMENTS IN NORTHERN INDIANA

I monitored 278 Wood Thrush (Hylocichla mustelina) nests in 14 forest fragments (range 7 to 500 ha) in northern Indiana to explore patterns of brood parasitism by Brown-headed Cowbirds (Molothrus ater), nest predation, and reproductive success. Density of thrushes was negatively related to area of forest fragments. Cowbirds were common throughout the landscape, but I found no relationship between their abundance and forest area. Overall, 90% of the thrush nests were parasitized by cowbirds (x̄ = 2.4 cowbird eggs per nest). The number of cowbird eggs per thrush nest was not related to forest area, abundance of host species, or distance to a forest edge but was positively related to thrush abundance. Nest predation rates averaged 58% and were lower than those reported in much of neighboring Illinois but also were unrelated to forest area and distance to a forest edge. The combination of cowbird parasitism and nest predation resulted in relatively low reproductive success (x̄ = 0.6 thrush fledglings per nesting attempt). I estimated that Wood Thrushes in northern Indiana made an average of three nesting attempts per breeding season (based on 17 color-marked females) and had relatively low seasonal fecundity (x̄ = 0.9 female fledglings per adult female per season). Nonetheless, considerable annual variation in seasonal fecundity suggested that some sites exceeded the source-sink threshold in some years. Regardless, the overall landscape appeared to be part of a regional sink for Wood Thrushes, although its negative influence on regional demography was not as severe as elsewhere in the midwestern United States. The poor demographic balance in much of the agriculturally dominated Midwest suggests that conservation efforts for Wood Thrushes and other Nearctic-Neotropical migrants should be directed at preserving and enhancing possible source habitats in regions where parasitism by cowbirds and nest predation are reduced.

DEMOGRAPHY OF BELL'S VIREOS IN MISSOURI GRASSLAND-SHRUB HABITATS

Abstract Numbers of Bell's Vireos (Vireo bellii) have declined throughout much of the breeding range in recent years, yet little information exists to determine factors that are causing these declines. We studied Bell's Vireos nesting in grassland-shrub habitats at two study areas in central Missouri to determine reproductive performance, survival, and population growth potential. Birds were color banded and observed during the breeding seasons of 1996, 1997, and 1998 to determine seasonal fecundity. We monitored 124 breeding pairs (127 pair years) and 213 nests. Density declined from 1.00 to 0.80 territories per 10 ha at the first site and increased from 1.11 to 1.33 at the second site during the study. Mean nesting success was 31 ± SE of 0.03% overall and ranged from 13 to 42% among years and study areas; 57% of the pairs fledged at least one young. Low annual production was a function of high rates of nest predation (41% of all nests observed, accounting for 44 to 78% of daily nest mortality annually) ...

A Model to Predict Breeding-Season Productivity for Multibrooded Songbirds

Breeding-season productivity (the per capita number of offspring surviving to the end of the breeding season) is seldom estimated for multibrooded songbirds because of cost and logistical constraints. However, this parameter is critical for predictions of population growth rates and comparisons of seasonal productivity across geographic or temporal scales. We constructed a dynamic, stochastic, individual-based model of breeding-season productivity using demographic data from Wood Thrushes (Hylocichla mustelina) in central Georgia from 1993 to 1996. The model predicts breeding-season productivity as a function of adult survival, juvenile survival, nesting success, season length, renesting interval, and juvenile-care intervals. The model predicted that seasonal fecundity (number of fledglings produced) was 3.04, but only 2.04 juveniles per female survived to the end of the breeding season. Sensitivity analyses showed that differences in renesting interval, nesting success, fledglings per successful nest, and adult and juvenile survival caused variation in breeding-season productivity. Contrary to commonly held notions, season length and fledgling-care interval length did not cause variation in breeding-season productivity. This modeling exercise emphasizes the need for demographic data for songbird species, and we encourage biologists to use similar models to evaluate productivity in songbird populations.

The Relative Impacts of Nest Predation and Brood Parasitism on Seasonal Fecundity in Songbirds

The impacts of nest predation and brood parasitism on the seasonal fecundity of birds are strongly dependent on the number of nesting attempts, and thus seasonal fecundity is responsive to behavioral traits that increase the number of opportunities to nest. We developed simple models to investigate the relative impacts of nest predation and brood parasitism on seasonal fecundity in songbirds. In particular, we asked to what extent songbirds can ameliorate the negative effects of high nest predation and brood parasitism often typical of fragmented, urbanized, and agricultural landscapes through (1) renesting following predation, (2) abandoning and renesting following parasitism, and (3) double brooding—renesting following a successful brood. Our model assigned probabilities to all possible fates of breeding females and calculated seasonal fecundity by summing up the individual probabilities. We analyzed the model through the use of fecundity isopleths, which allow one to visually determine the impact of predation and parasitism simultaneously over the entire range of probabilities. Our analysis indicates that (1) nest predation has a greater impact on seasonal fecundity over a larger range of parameter space than does parasitism, especially when brood loss due to parasitism is low; (2) songbird populations experiencing nest predation probabilities typical of fragmented landscapes (>0.65) are unlikely to be self‐sustaining; and (3) amelioration of nest predation through frequent renesting or double brooding may be insufficient to establish self‐sustaining populations. These results suggest that predator control should be at least as high a priority as parasitism control, particularly for species that suffer moderate to low brood reduction due to parasitism and that are single‐brooded. Programs aimed solely at managing cowbirds likely will be of limited success.

Brood Parasitism, Nest Predation, and Season-Long Reproductive Success of a Tropical Island Endemic

The Puerto Rican Vireo (Vireo latimeri) is a single-island endemic resident on Puerto Rico. The Shiny Cowbird (Molothrus bonariensis), a generalist brood parasite native to South America, arrived on the island in 1955 and has established itself as a breeding resident. To determine the impact of the exotic cowbird on vireo reproductive success, I studied the demography of marked Puerto Rican Vireos in Guanica Forest, Puerto Rico, in 1990-1993. Vireo breeding season length varied among years (69-106 days), apparently influenced by rainfall. The primary causes of reproductive failure were nest parasitism and nest predation. Cowbirds parasitized 73-83% of vireo nests. Parasitism reduced the number of vireos fledged per successful nest by 82%, primarily through decreased hatching success and fledging success. Vireos did not abandon nests in response to cowbird egglaying, but frequently deserted if cowbirds removed host eggs. Native avian predators and exotic mammalian predators together caused the demise of about 70% of all nest attempts. As a result, daily nest survival rate was low (0.93 ± 0.01), and only 13-19% of nests fledged vireo or cowbird young. Pairs renested after failure and attempted to raise second broods. Females in this population attempted two to six nests per season and fledged an average of 1.33 vireos in 1991 and 0.24 vireos in 1993. The combination of restricted breeding season, high predation and parasitism rates, large impact of parasitism on reproductive output, and low seasonal fecundity of females suggests that, despite high survival rates, the Puerto Rican Vireo is in danger of extirpation from portions of its range.

Reproductive cycling and fecundity estimation in the upland bully

The upland bully is a prolific and widespread member of New Zealand freshwater fish communities that may mature at age 1 (or earlier). It begins spawning in spring, laying as many as eight clutches of eggs over the spring and summer, at periods as brief as 13 days. Ovaries contain two modes of maturing oocytes, so that oogenesis must be continual during the spawning season. This poses difficulties in fecundity estimation, which were solved by captive rearing. The ovoid eggs are about 2 mm long; egg size declines with clutch number during the summer, but increases with fish size. Clutch size varied, in 70 spawnings, from 121 to 880 eggs, with total seasonal fecundity up to >5000 eggs. The production of multiple clutches greatly increases seasonal fecundity and may explain the success of this species in sometimes unreliable or harsh environments.

Assessing the Consequences of Brood Parasitism and Nest Predation on Seasonal Fecundity in Passerine Birds

-Brood parasites and nest predators reduce the seasonal fecundity and, hence, the population growth rates of their victims. However, most field studies do not measure directly how parasites and predators decrease seasonal fecundity, but instead measure the impact of these organisms on individual nesting attempts. Because a female may renest after losing a nest to predation, abandoning a parasitized nest, or successfully fledging a brood, knowing how brood parasites and nest predators reduce the number of offspring fledged from individual nesting attempts is not equivalent to knowing their impact on seasonal fecundity. We address this problem by developing a mathematical model that: estimates several parameters describing the natural history of this system, including the brood-parasitism rate, nest-predation rate, and probability of nest abandonment in response to a parasitism event; and extrapolates to seasonal fecundity from these parameters and others describing the length of the breeding season, the timing of events in the nesting cycle, and the productivity of parasitized and unparasitized nests. We also show how different researchers using different observational methodologies to study exactly the same population likely would arrive at noticeably different conclusions regarding the intensity of brood parasitism, and we provide mathematical formulas for comparing among several of these measures of parasitism. Our procedures extend Mayfield's method for calculating nest-success rates from nest-history data in that we simultaneously estimate parameters describing nest predation and brood parasitism, predict seasonal fecundity from these parameters, and provide confidence intervals on all parameter estimates. The model should make the design and interpretation of logistically difficult empirical studies more efficient. It also can be specialized to species affected by nest predators but not brood parasites. We use the model to analyze Prairie Warbler (Dendroica discolor) and Black-capped Vireo (Vireo atricapillus) nesting data. We estimate the model's parameters for these species and use the resulting estimates to predict seasonal fecundity. For both species, the predicted seasonal fecundity closely matches the value measured directly. Received 30 November 1993, accepted 15 February 1994. BROOD PARASITES AND NEST PREDATORS cause many passerine nests to fail before any young are fledged (Ricklefs 1969). In addition, when a parasitized nest is not immediately abandoned, the number of host young that can be fledged is often greatly reduced. As Rothstein (1990) summarized, about 80 bird species are interspecific brood parasites, including cowbirds (Emberizidae, Icterinae), cuckoos (Cuculidae, Cuculinae and Neomorphinae), the Cuckoo-finch (Anomalospiza imberbis), whydahs (Ploceidae, Viduinae), honeyguides (Indicatoridae), and the Black-headed Duck (Heteronetta atricapillus; Friedmann 1929, 1955, Weller 1959, Payne 1977, Wyllie 1981). Nest predation is known from all passerines studied in any detail, and includes predation by small mammals, birds,

A hierarchical response to differences in ration size in the reproductive performance of female three‐spined sticklebacks

The response of female three‐spined sticklebacks (Gasterosteus aculeatus) to differences in food ration during the breeding season was quantified for several variables related to reproductive performance. The measured protein and lipid contents (mg g−1) of eggs were unaffected by ration. Egg size increased with an increase in both ration and female size, but the proportional increase in egg size was much smaller than the proportional increase in ration. The best predictor of mean batch (clutch) fecundity and weight was female size. There was a small but significant increase in batch fecundity with ration, but the increase was not directly proportional to the increase in ration. The rate of spawning, total breeding season fecundity and total weight of eggs spawned over the breeding season were sensitive to ration with breeding season fecundity and weight increasing in direct proportion to ration. Thus, in female sticklebacks, there is a hierarchy of sensitivity to ration in the response of variables related to reproduction.

The effect of management history and time of mating on ovulation and lambing rates in mule ewes

There is increasing interest in the development of later lambing systems for crossbred ewes which more closely match ewe nutritional requirements with herbage growth (Stone, 1988; Mitchell, 1990). It has long been recognised however that at extremes of the natural breeding season fecundity is reduced, a possible consequence of seasonal variations in ovulation rate, fertilisation and/or embryo survival (Hammond, 1944). Daylength is the factor which entrains the endogenous rhythm of reproduction in sheep (Donovan, O’Callaghan, Karsh, Boland and Roche, 1992) and daylength changes per se may be responsible for variations in reproductive response throughout the breeding season. Associated environmental and management factors may also be of importance. The objective of the present study was to determine the effect of management history and month of mating on ovulation and lambing rates in Mule ewes.

The effect of management history and time of mating on ovulation and lambing rates in mule ewes

There is increasing interest in the development of later lambing systems for crossbred ewes which more closely match ewe nutritional requirements with herbage growth (Stone, 1988; Mitchell, 1990). It has long been recognised however that at extremes of the natural breeding season fecundity is reduced, a possible consequence of seasonal variations in ovulation rate, fertilisation and/or embryo survival (Hammond, 1944). Daylength is the factor which entrains the endogenous rhythm of reproduction in sheep (Donovan, O’Callaghan, Karsh, Boland and Roche, 1992) and daylength changes per se may be responsible for variations in reproductive response throughout the breeding season. Associated environmental and management factors may also be of importance. The objective of the present study was to determine the effect of management history and month of mating on ovulation and lambing rates in Mule ewes.

Daily Ovarian and Spawning Cycles in Weakfish

Abstract A spawning population of weakfish Cynoscion regalis in Delaware Bay was sampled on May 27, 29, and 30, 1988, to relate the daily timing of spawning to the ovarian cycle. Spawning was concentrated over several hours in early evening, ending soon after sundown. Female gonadosomatic index (GSI), proportion of females with hydrated oocytes, and percentage of hydrated oocytes in ovaries were all at or near daily maxima at 1700 hours and declined precipitously by 2000 hours. Although all females examined contained hydrated oocytes on each of the three nights of the study, GSI, numbers of hydrated oocytes, and fecundity decreased by the last night. These results suggest that individual female weakfish spawned for several days in succession and became, at least temporarily, depleted by the end of that period. Sampling on June 10, 13, and 21 documented additional spawning by fish in the size range collected in May, but GSI and fecundity were lower in the June collections. Estimation of seasonal fecundity ...

The role of selected environmental factors and sex ratio upon egg production in three-spine sticklebacks, Gasterosteus aculeatus

We compared the fecundity of female sticklebacks (Gasterosteus aculeatus) breeding in salt marsh tide pools with that of fish breeding in the laboratory. Although total egg production was higher in the laboratory, there was no significant difference in clutch sizes between the two groups. In the field, physicochemical factors (water temperature, levels of dissolved oxygen, pH, and salinity) explained a statistically significant but small amount of the variation in the various measures of reproduction (daily egg production, total egg production, clutch size, interspawning interval) used. The results of a laboratory experiment concerning the effect of sex ratio upon female reproduction showed that this variable had little effect. The time spent on the breeding grounds appears to be the principal factor determining the seasonal fecundity of this species.