Variation In Breeding Success Research Articles

Consequences of recruitment decisions and heterogeneity on age‐specific breeding success in a long‐lived seabird

An individual's age at first reproduction and investment in successive reproductive attempts are involved in mechanisms that can impede somatic repair, resulting in a decline in reproductive abilities with age (reproductive senescence). We used long-term data from the Black-legged Kittiwake, a long-lived seabird, to address the relationship between recruitment age, age-specific breeding success (BS), and reproductive senescence, while accounting for breeding experience and temporal variation in BS. We first detected late-life improvement in BS across all recruitment groups, which we recognized as "within-generation selection" or the selective disappearance of "frail" phenotypes. When such heterogeneity was accurately accounted for, we showed that all individuals suffered reproductive senescence. We first highlighted how different combinations of pre- and post-recruitment experience across recruitment groups resulted in maximal BS at intermediate ages. BS increased in early recruits as they gained post-recruitment experience, whereas late recruits gained pre-recruitment experience that led to high BS at recruitment. Only individuals recruiting at intermediate ages balanced their pre- and post-recruitment experience. Consistent with the "cumulative reproductive cost hypothesis," we also observed a faster decline in BS in early recruits at advanced ages, whereas individuals delaying recruitment experienced the slowest decline in BS with age. Early recruits, however, reached the highest levels of BS at intermediate ages, sensus stricto (10-13 years old), whereas individuals delaying recruitment experienced the lowest at similar ages. These divergent trajectories may reflect a "delayed trade-off" balancing a maximization of midlife BS against reproductive senescence at advanced ages. Additionally, annual variation in BS had a greater effect on individuals early in life, suggesting that experienced individuals were able to buffer out the effects of temporal variation on BS, which can ultimately improve fitness in stochastic environments. Our findings stress that (1) both observed and unobserved heterogeneity are important in detecting within-individual senescence, and (2) short-term trade-offs may be rare in long-lived species; thus, cumulated reproductive costs should be invoked as an alternative mechanism underlying reproductive senescence.

Variable but predictable prey availability affects predator breeding success: natural versus experimental evidence

AbstractFood supply is a major source of variation in breeding success for predators, and to what extent individuals are able to cope with temporal variability in food availability remains an outstanding question in life‐history studies. We confronted the natural variation in clutch size and breeding success with results from a food supplementation experiment during egg formation, conducted over several contrasted years of natural food supply in an avian specialist predator, the Montagu's harrier Circus pygargus. This raptor mainly preys on common vole Microtus arvalis a cyclic microtine under temperate latitudes. Vole abundance together with timing of breeding accounted for most of the variance in clutch size and number of fledglings. Results from empirical and experimental data were overall in agreement. Fed pairs consistently increased clutch size compared with controls in all experimental years, whereas no effect of food supplementation on egg volume was detected. Supplemented pairs, however, did not fledge significantly more chicks than controls. The costs entailed by the increase in clutch size appear nevertheless to be limited compared with previous studies. Food supply seemed therefore to display sufficient predictability throughout a breeding season to afford individuals the opportunity to adjust their breeding effort to an optimal number of offspring, in agreement with Lack's anticipation hypothesis.

Subcolony Variation in Breeding Success in the Tufted Puffin (Fratercula Cirrhata): Association With Foraging Ecology and Implications

Abstract Large-scale oceanographic processes are the main drivers of seabird breeding success, but small-scale processes, though not as well understood, can also be important. We compared the success of Tufted Puffins (Fratercula cirrhata) breeding at two subcolonies only 1.5 km apart on Triangle Island, British Columbia, Canada, 2002–2005. In addition, we used stable-isotope analysis to test the hypothesis that parental foraging strategies differed between the two subcolonies, potentially underlying the variation in breeding success. Success was concordant across years at the two sites but, overall, Tufted Puffins bred more successfully at Strata Rock than at Puffin Rock. They raised chicks in all four years at Strata Rock, but in only three years at Puffin Rock; in two of those three years, Strata Rock chicks were, on average, 60 g and 100 g heavier than Puffin Rock chicks just before fledging. Discriminant analysis of carbon and nitrogen stable-isotope ratios in egg yolk and chick blood in 2004 and 2005 indicated that parental foraging differed between the two subcolonies, with both spatial (δ13C) and trophic-level (δ15N) differences involved. Thus, our study demonstrates the existence of foraging asymmetries in a pelagic seabird at a small spatial scale (between subcolonies), complementing patterns found at larger scales (between colonies). Moreover, the foraging asymmetries were associated with inequalities in fitness measures. We conclude that small-scale processes—in this case, systematic differences in the foraging ecology of local groups—can interact with large-scale oceanographic processes to determine seabird breeding success. Variation sous-coloniale du succès de reproduction de Fratercula cirrhata: Association avec l'écologie de la quête alimentaire et implications

Individual Variation in Behavior and Breeding Success of Northern Fulmars

-In a sample of breeding Northern Fulmars (Fulmarus glacialis) observed in 45 years, up to 43% of the variability in 13 attributes of breeding behavior was consistent among individuals or pairs. Sample means for most attributes were correlated in a predictable way with annual levels of breeding success. Except for laying dates, there was little evidence that individual differences in these attributes contributed to variation in breeding success. A test of breeding experience as a contributing factor revealed an interaction between individual and annual components of variation. During years when the whole population did relatively poorly, pairs with no previous breeding experience were affected disproportionately. Late-nesting fulmars were more successful than early layers, possibly because delayed breeding ensured that food availability was adequate for successful incubation. Received 7 November 1989, accepted 15 May 1990. IF the same sample of breeding birds is monitored in several years, the observed variance in breeding success has annual and individual components. Annual variation arises from variability in environmental factors such as food supply, predation, disease, weather, or disturbance. Any added component of individual variation arises from differences in the quality of the habitats occupied by individuals (Nettleship 1972, Birkhead 1977, Hudson 1982), or from differences in the quality of the individuals themselves (Coulson 1968, Potts 1969, Reilly and Cullen 1981). Interaction between the two components of variation is expected because annual changes in the environment need not affect all individuals equally. In a 6-yr study of breeding Northern Fulmars (Fulmarus glacialis), I found that young were more likely to be raised successfully in some sites than others (Hatch 1988). Fulmars are longlived and have a strong fidelity to the same mate and nest site between years (Hatch 1987, 01lason and Dunnet 1988). Many of the birds in my sample were individually known from plumage differences, and all direct evidence indicated that few undetected changes of site ownership or pair bonds occurred during the study. I therefore hypothesized that the amongpairs component of variance in breeding success could be explained by individual differences in I Present address. breeding biology and behavior. Consequently, I assessed individual variation in laying dates and time allocation as factors that affect breeding success. I also considered the influence of breeding experience under the varying conditions that occurred during the years of study.

Testing for Individual Variation in Breeding Success

Testing for Individual Variation in Breeding Success

Seasonal Variations in Breeding Success of Common Terns: Consequences of Predation

We studied the breeding of 125 pairs of Common Terns (Sterna hirundo) in a large colony at Monomoy, Massaschusetts, in 1979. The colony was subjected to predation by one or more Great Homed Owls (Bubo virginianus). The adult terns deserted the colony for 6.5-8 hours each night throughout the season. Although the owl(s) took no adults and only about 20 chicks from our study plots, the terns suffered unusually heavy losses from other causes, including breakage and disappearance of eggs, hatching failures, attacks by ants (Lasius neoniger), chilling of newly-hatched chicks, and predation by Black-crowned NightHerons (Nycticorax nycticorax). In a 10-year study, most of these causes of egg and chick loss have been associated with nocturnal desertion and predation by Great Horned Owls. Although nocturnal desertion is effective in minimizing owl predation on adults, it leaves the eggs and chicks vulnerable to chilling and predation. In 1979, both direct and indirect effects of predation fell more heavily on terns that laid in May than on terns that laid in June. Differential predation on early nesters tends to offset other factors that presumably favor early nesting. Predation is one of the most important selective forces influencing breeding behavior in ground-nesting colonial birds, such as gulls and terns (Lack 1968). When a nocturnal predator gains access to a colony, larids usually have no effective defenses (Austin 1948, Ashmole 1963, Southern et al. 1982). However, avian predators and diurnal mammals often take only limited numbers of colonial larids (Hatch 1970, Nisbet 1975, Southern et al. 1982). Consequently, the study of differential mortality in a larid colony can throw light on the role of predation in influencing timing, synchrony, and spacing behavior (Ashmole 1963, Kruuk 1964, Patterson 1965, Tinbergen 1967, Parsons 1971, Nisbet 1975). Nisbet (1975) reported that Great Horned Owls (Bubo virginianus) preying on nesting Common Terns (Sterna hirundo) took a much higher proportion of chicks hatched earlier in the season than of chicks hatched later. We describe here a study of another Common Tern colony subjected to predation by one or more Great Homed Owls. In the case described here, direct predation by the owl(s) was less important than other causes of egg and chick losses. However, we present evidence that at least some of these other losses were indirect consequences of the owl's activity. This paper analyzes seasonal variations in both direct and indirect effects of owl predation. STUDY AREA AND METHODS We studied 125 pairs of Common Terns within a colony of about 3,300 pairs at Monomoy National Wildlife Refuge, Massachusetts (41038'N, 69058'W) in May-August 1979. This was part of a long-term study of this colony, whose results are summarized in Table 1. In 1979, we selected two study plots about 75 m apart, comprising a total area of about 570 m2. Each plot was on the edge of a large open sandy area surrounded by dense beach grass (Ammophila breviligulata). Common Terns nested earliest and most densely in a partially vegetated border strip containing scattered clumps of live and dead beach grass, seaside goldenrod (Soli ago sempervirens) and beach pea (Lathyrus japonica). Although both study plots included areas of dense grass and open sand, Common Terns occupied these habitats later and less densely than the border strips. The plots were selected to be representative of the whole colony, and the density and patterns of occupation appeared similar in other parts of the colony. We visited the study plots on most days from 22 May to 9 July, on 20, 21 and 28 July, and on 7 August 1979. P. Trull visited the colony n five other days between 10 and 25 July. N ts and eggs were marked when first seen, and eggs were weighed. When eggs were not found on the day of laying, this date was estimated from laying and hatching patterns and by flotation (Hays and LeCroy 1971); weights of fresh eggs were estimated from data on the rate of weight loss (Rahn et al. 1976). Nine banded adults, including two nesting outside the plots, were trapped to determine their ages. Chicks were banded at hatching and checked

Components of Avian Breeding Productivity

Numbers of nestlings fledged per pair per season were calculated for 35 species of passerine birds in four localities from data on length of breeding season, clutch size, nesting mortality, and length of nest cycle. Mean numbers of nestlings fledged was 6.42 for 12 woodland and edge species in Kansas, 4.33 for 8 species in lower Sonoran desert habitat in Arizona, 2.36 for 6 species in humid forest and second-growth habitats in Costa Rica, and 4.80 for 9 species in a desert scrub habitat in Ecuador. The data were analyzed by multiple correlation and stepwise multiple regression to determine the contribution of the variables to variation in the number of young fledged from one species to another in each locality. Variations in season length, clutch size, and breeding success were important components in variation in numbers of young fledged in Kansas, but length of nest cycle, being positively correlated with both clutch size and nest success, had the strongest correlation with the number of young fledged. In Arizona and Costa Rica, variation in breeding success held the key to predicting variation in number of young fledged, whereas in Ecuador season length and clutch size were the critical variables. The analyses suggest that data on production of young and the factors that cause production to vary from one species to another would add immensely to our understanding of the population ecology of birds.-Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19174. Accepted 1 July 1975. Ornithologists have pondered the significance of clutch size in birds for nearly three decades without fully resolving the factors responsible for its variation among species and regions. Although Skutch (1949) linked the evolution of clutch size to adult mortality and population turnover rate, population biologists have only re- cently placed clutch size in a demographic context. For example, not until 1961 did Drury point out that the production of young by a pair of birds during a breeding season depends on the number of broods raised as well as clutch size. Cody (1971) and Ricklefs (1973) treated avian demography more fully and demonstrated the use of life table analyses to compare species. Although breeding biology and mortality have been investigated in scores of de- tailed field studies, complete life tables have been constructed for only a handful of species. Of the statistics required to complete a life table, the annual production of young is one of the most difficult to obtain. Observation of individually marked birds yields relatively few data per hour of effort (for example see Nice 1937, Snow 1958). Furthermore, estimates of mean annual productivity obtained from direct observa- tion have large probable errors (wide confidence limits) owing to the great variation between individuals. Annual productivity can be calculated indirectly from clutch size, breeding success, nest cycle length, and length of breeding season (Ricklefs 1970). These data are more readily obtained than direct measures of breeding pro- ductivity. Furthermore, data from different studies may be combined to calculate the annual production of a species. In this paper we calculate annual production (fledglings per pair of adults) for various passerine birds in two temperate and two tropical localities. The data are