Maximum Clutch Size Research Articles

Incubation capacity and clutch size determination in two calidrine sandpipers: a test of the four-egg threshold.

Several groups of vertebrate taxa, including shorebirds, are unusual in that they produce a fixed number of offspring. The aim of this study was to examine whether the incubation capacity of western sandpipers (Calidris mauri) and semipalmated sandpipers (C. pusilla) limits their maximum clutch size to four eggs. Experimental enlargement of clutch size had no effect on rates of nest abandonment, nest attendance or loss of body mass by incubating sandpipers. The duration of incubation was significantly longer for enlarged five-egg nests, and there were trends towards increased partial clutch loss and asynchrony at hatch, but overall hatching success was unaffected by experimental egg number. I conclude that small, calidrine sandpipers with biparental care are able to compensate for an additional egg in an enlarged nestbowl, despite the constraints of conically shaped eggs and two brood patches. Possibly, shorebirds do not lay more than a fixed clutch size of four eggs because selection on factors acting during egg production or brood-rearing is more important in regulating offspring number.

Observations on the life history of Orchomene nanus (Krøyer) (Amphipoda: Lysianassoidea) at Millport, Scotland as deduced from baited trapping

Orchomene nanus (Krøyer) was captured in funnel traps baited with crushed crabs [ Carcinus maenas (L.)]. Monthly field samples were collected for population analysis over one year. Male Orchomene nanus can be distinguished most effectively from females and juveniles on the basis of the number of articles in antenna 2 flagellum. This flagellum becomes more elongate at each moult after sexual differentiation. The acquisition of calceoli reflects sexual maturation in males, as does a setose brood pouch in females. Analysis of the amalgamated size-frequency data for all seasons, allowed recognition of putative moult stages and calculation of moult-to-moult growth factors throughout the life of an individual (estimated to be 13 instars). Sexual differentiation occurred at instar 5 and maturity at instar 8. Males may live slightly longer than females. Females are iteroparous, producing three, perhaps four, broods. A two-generation life cycle involving a short-lived (7mo), fast growing summer generation and a longer-lived (12 months), slower growing generation that overwinters is hypothesized. Ovigerous females were present virtually year-round (none was recorded in October or January), resulting in domination of the population by juveniles for most of the year. Fecundity was related to female body size. Maximum clutch size was 26; with a lifetime potential fecundity calculated to be 27–52 eggs. Eggs doubled in volume during marsupial development. That hatchlings were under-represented in the collections could be due to sampler deficiencies (mesh size), or to behavioural differences, cf. adults. In most samples, the sex ratio was not significantly different from 1:1. However, a tendency toward female dominance was apparent overall (with the proviso that inaccuracies associated with recognition of the smallest males may have contributed to this finding).

Egg production in three species of Antarctic Calanoid Copepods during an austral summer

Egg production in three species of calanoid copepods Rhincalanus gigas, Calanoides acutus and Calanus simillimus was investigated via incubations of females and recovery of eggs from net hauls made around South Georgia during January 1993. Average daily egg production was highest for the sub-Antarctic C. simillimus, (15.5 eggs female −1 d −1). This species normally spawns in the spring in the central part of its geographical range but was apparently delayed by the colder waters found around South Georgia. For R. gigas and C. acutus egg production averaged 8.9 and 6.0 eggs female −1 d −1, respectively. The former species appeared to be undergoing protracted recruitment while the population of the latter was preparing to overwinter. Considerable interstation variability existed, although no relationships were apparent between surface chlorophyll concentrations and either egg production in experiments or in the numbers of eggs recovered by the nets. Clutch size (eggs produced spawning female −1 d −1) did not differ significantly between the three species although the maximum clutch size recorded for R. gigas (94 eggs) was almost twice that of C. simillimus. Samples taken from the Bellingshausen Sea during the latter part of 1992 indicated that recruitment of R. gigas and C. acutus commenced in early December in this region when adult females were concentrated in the surface 250 m and a diatom bloom was developing. Egg numbers were highest in the surface 50 m (up to 350 m −-3) at both the Bellingshausen and South Georgia stations. At the latter site females migrated into these surface layers at night; thus it would appear that spawning is largely nocturnal and linked to diurnal migratory behaviour.

Effects of Experience and Body Weight on Incubation Behavior of Canada Geese

Abstract During 1979 and 1980, we studied the incubation behavior and body-weight dynamics of captive Canada Geese (Branta canadensis moffitti) with known breeding histories. Females were attentive to their nests for 97.5% of the incubation period and lost 27% of their initial body weight. Heavier females were more attentive to their nests and lost more weight during incubation than did lighter females. Variation in body weight among females was greatest at the onset of incubation and least at hatch, which suggests that females invested maximum reserves in incubation. Recess frequency and duration increased throughout incubation, resulting in more foraging time for the female. Once a lower critical weight of about 3,200 g was reached, the amount of recess time taken increased dramatically, probably because lipid reserves were depleted. Females nesting for the first time began incubation at a lighter body weight and were less attentive than experienced females. All inexperienced females were either 4 or 5 yr old, but their egg production (4 eggs) was that of 2- or 3-yr-old wild females. This indicated that experience rather than age was the important variable affecting acquisition of reserves. Inattentiveness to a nest by a female prolongs the duration of incubation and exposes the nest to a greater risk of predation. The inability of inexperienced females to gain enough reserves to provide for both maximum clutch size and attentiveness during incubation may be a major explanation for the lower hatching success of geese nesting for the first time.

Observations on the reproductive biology of the land tortoises Geochelone emys and Geochelone yniphora in the Honolulu Zoo

AbstractCaptive reproduction of the Burmese brown tortoise (Geochelone emys) has occurred repeatedly over a five‐year period in the Honolulu Zoo. Maximum clutch size (51 eggs) exceeds that reported for other members of the Testudinidae. Nesting behavior in G emys includes construction of a large leaf‐litter mound. Collection of nest‐building material is accomplished by “back‐sweeping” of ground litter within a distance of up to 4 m from the nest site. The nesting female assumes a “nest‐guarding” behavior for a period of 2–3 days following egg laying. Eggs incubated artificially hatched in 63–84 days, with egg fertility at 78–84%. One hundred and three G emys were successfully hatched and reared during the period 1978–82.A colony of endangered Madagascar angulated tortoises (Geochelone yniphora) have been maintained at the Honolulu Zoo since 1971. Courtship and mating behavior is similar to that described for the consubgeneric G radiata. Distinctive male “hooking” behavior during courtship in G yniphora is related to the exaggerated epiplastron development in this species. Egg laying has occurred repeatedly in the G yniphora colony since 1979 (mean clutch size = 4.2; N = 6) although no eggs have yet proved fertile.

Relationships between Jackrabbit Abundance and Ferruginous Hawk Reproduction

-From 1966-70 and 1972-74, we studied relationships between Ferruginous Hawk (Buteo regalis) reproduction and abundance of their main prey, the black-tailed jackrabbit (Lepus californicus) in the eastern Great Basin Desert of central Utah. Correlation tests showed significant relationships between jackrabbit abundance and hawk reproduction: the population of nesting hawks, number of nesting pairs, total eggs laid and total young fledged varied in synchrony with jackrabbit abundance. Key Factor Analysis and stepwise removal procedures indicated that jackrabbit abundance influenced hawk reproduction in the following order of decreasing importance: number of nesting pairs; failure of nesting pairs to achieve maximum clutch size; total number of young fledged and total number of young hatched. Regression tests revealed that two of these, the failure to nest and achieve maximum clutch size, are important limiting factors on reproduction and at least partially act to regulate the size of this Ferruginous Hawk population. Solomon (1949) proposed that predators respond to changing prey densities in two basic ways, functionally and numerically. In the functional response, a predator consumes prey of a given species at a rate according to the density of prey. In the numerical response, predator population density changes with changing prey density, usually through migration and/or corresponding adjustments in reproduction

Reproductive effort and life history strategy of the Aldabran giant tortoise

THE Aldabra giant tortoise, Geochelone gigantea Schweigger, has a large body size (19–120 kg)1, long life span (65–90 yr)2, late maturity (females 17–23 yr)3,4 and iteroparity3. The three isolated island populations of different densities on Aldabra show dissimilarity in their reproductive parameters (for example mean clutch size, mean egg weight, proportion of mature females breeding and the number of clutches per female per year) and in the variation of these parameters from year to year through annual changes in rainfall3. Moreover, their reproductive response to these changes in rainfall is rapid; they have a relatively high maximum (potential) rate of natural increase (maximum clutch size 28)3 and mature females in the high density population are half the weight of those in the low density area2,4. I have postulated that the reproductive effort would differ between the different density populations and that this effort would change in relation to changes in food availability. This contention is supported by the results reported here.