Mate availability affects female choice in a fish with paternal care: female counterstrategies against male filial cannibalism

Theory predicts that individuals should adopt counterstrategies against intersexual conflict with their mating partners if the counterstrategies are effective and cost-efficient. In fishes, males with parental care often cannibalize their own offspring, which reduces the female’s fitness and creates intersexual conflicts. Males of the goby Rhinogobius flumineus cannibalize more eggs in the nest when they have access to additional females prior to spawning. Thus, it is predicted that females will strategically avoid spawning with males that have high mate availability. In the present study, we experimentally tested this prediction. When sexual pairs were placed in tanks, most females (control females; 21/22) successfully spawned inside the nest. In contrast, when a gravid female (stimulus female) that was housed in a small transparent cage was shown to the experiment pairs prior to spawning, only about half of the females (experiment females; 16/29) spawned inside the nest; the remaining females released unfertilized eggs outside of the nest. Moreover, experiment females infrequently accepted and followed males into nests, and delayed spawning more often than control females. R. flumineus females prefer males that court frequently. Indeed, experiment females that infrequently received courtship tended to spawn outside of the nest. However, infrequent courtship alone could not explain outside-nest spawning, delay in spawning, or the shorter stay of females in nests. These results imply that the presence of a stimulus female dampens female spawning with males. We suggest that R. flumineus females may strategically reject or hesitate to spawn with males that have high mate availability, and that this spawning avoidance may be a counterstrategy against male filial cannibalism.     

Filial cannibalism in an assassin bug

Filial cannibalism has been described in many fish species with male parental care, and has typically been explained as a response to high energetic costs of brood defence and decreased feeding opportunities during the period of care. We investigated filial cannibalism in an insect, the assassin bug Rhinocoris tristis. In this species, males guard eggs of a number of females, cannibalizing some of their offspring within the brood. We monitored guarding males in both the field and the laboratory. Males typically ate eggs around the periphery of the brood, which were those most likely to have been parasitized by wasps. However, cannibalism persisted in the laboratory in the absence of parasites, and the number of cannibalized eggs was related to the length of care and overall brood size, suggesting that males use eggs as an alternative source of food. This conclusion was further supported by the fact that males in the field did not lose weight while guarding, despite being unable to forage efficiently while caring. Males were also observed to adopt broods, but in a laboratory experiment did not eat more eggs from adopted than from their own broods.     

The cost of peripheral males in a brook trout mating system

A focus on the reproductive contributions of males displaying alternative life histories has neglected the role of size-dependent peripheral males in salmonine mating systems. We documented mating behaviour of brook trout Salvelinus fontinalis, including observations of spawning, over two breeding seasons to determine the mating costs of peripheral males to dominant males (kleptogamy) and females (egg cannibalism). For males and females, the mating costs of peripheral males were substantial because more than half (56%) of all observed brook trout spawnings involved peripheral males. Males that paired with large females experienced a greater incidence of kleptogamy due to increased numbers of peripheral males present. Large males face a conflict when mating in that they prefer to spawn with large females; however, these same females attract numerous males against which the dominant male cannot defend. From paternity studies, we estimated that males that had peripheral males participate in spawning may fertilize, on average, equal numbers of eggs compared to males spawning solely with a smaller female. Females that paired with relatively smaller males had significantly more eggs eaten by peripheral males than females that paired with relatively larger males. Latency to spawn by females increased when paired with a relatively small male, and resulted in females obtaining a larger spawning partner. The observed patterns of size-assortative mating, kleptogamy and cannibalism are discussed in relation to mate choice for this population of brook trout. Copyright 1999 The Association for the Study of Animal Behaviour.     

Dummy Egg Production by Female Cardinalfish to Deceive Cannibalistic Males: Oogenesis without Vitellogenesis

Filial cannibalism occurs in a variety of taxa, especially in fish exhibit paternal care. In the Apogonidae, males mouthbrood a cohesive mass of eggs received from a single female, although the males frequently eat the entire brood. It has been recognized that a primary factor concerning entire brood cannibalism is the brood size produced by females, as the parent eats a small egg mass so long as the reproductive return does not exceed the cost of providing care. In Apogon lineatus, approximately 18% of each brood was occupied by abnormal eggs lacking yolk, which were hydrated without the vitellogenesis phase and eventually ovulated with other normal eggs as a single egg mass. By not providing yolk to some eggs within the brood, A. lineatus females may succeed in producing an apparently large brood, reducing the likelihood of entire brood cannibalism by males.     

Brood conspicuousness and clutch viability in male‐caring assassin bugs (Rhinocoris tristis)

Abstract 1. Conspicuousness to mates can bring benefits to both males (increased mating success) and females (reduced search costs), but also brings costs (e.g. increased predation and parasitism). Assassin bugs, Rhinocoris tristis, lay egg clutches either on exposed stems or hidden under leaves. Males guard eggs against parasitoids. Guarding males are attractive to females who add subsequent clutches to the brood. This is an excellent opportunity to study the effects of conspicuousness on the fitness of males and females. 2. Using viable eggs in a multi‐clutch brood as a correlate of fitness, the present study examined whether laying eggs on stems affected (1) female fitness, through exposure to parasitism and cannibalism, and (2) male fitness, through attracting further females. 3. Stem broods were more parasitised. However, males on stems accumulated more mates and more eggs, a net benefit even accounting for parasitism. The eggs gained from being on a stem were cannibalised. By contrast, higher mortality on stems suggests that females should gain by ovipositing on leaves. To the extent that egg viability represents fitness, male and female interests may therefore differ. This suggests a potential for sexual conflict that may affect other species with male care. 4. Despite higher costs, females actually initiated more broods, and subsequently added bigger clutches to broods, on stems than under leaves. This suggests either that viable eggs do not reflect fitness, or that females laid in unfavourable locations. The key is now to address lifetime fitness, since unmeasured factors may affect offspring viability post‐hatching, and to investigate who controls the location of oviposition in R. tristis.     

Optimal Mate Searching Strategy in the Symbiotic Spider Crab Inachus phalangium (Decapoda)

The reproductive strategy of the symbiotic spider crab, Inachus phalangium was studied from 1981 to 1983 in the natural environment. Main study focus was the efficiency of males in search of mates. I. phalangium females are site-constant, and live in the protection of one anemone or group. Males travel frequently between anemones harbouring females due to spawn; they copulate and guard the females until spawning, after which the male leaves again. A male operates in a patrol area containing 3–8 anemone groups and up to 8 females, visiting each female in turn repeatedly just before it is due to spawn. Patrol areas of different males may overlap, with resulting competition to fertilize a female's next brood. Large males have higher reproductive success than small ones. Females live up to 8 months after the moult of puberty and hatch up to six broods, and males live up to 7 months as adults. A male could fertilize a calculated 26,000 eggs, whilst a female's reproductive potential is ca. 4,200 eggs. Mortality risks are higher for males than for females, probably because of increased predation while leaving the protection of anemones in order to visit females. Males learn the positions of anemones harbouring females in their patrol areas, and when these are due to spawn. This allows a male to travel with a target and arrive punctually to fertilize the next brood due in his circuit. I. phalangium is the first marine invertebrate reported to use a “schedule” of localities and times for visiting prespawning females. In this way males minimize searching time and mortality risk, and maximize the number of broods fertilized.     

A Test for Male Parental Care in a Fundulid, the Bluefin Killifish, Lucania goodei

Under field conditions, breeding male bluefin killifish, Lucania goodei, have been observed aggressively defending territories from other breeding males, non-breeding females, and minnows (mainly Notropis harperi). We performed an aquarium experiment to test whether male aggression serves to protect newly deposited eggs from predation. We allowed a male and a female to spawn in a yarn mop, removed the female, and exposed the eggs to one of four treatments (spawning male present, two minnows present, spawning mal+two minnows present, no adult fish present). Mops were censused daily for seven days. Egg predation rates were highest in the male+minnows and male only treatments. Egg predation rates in the male+minnows treatment did not differ from the predicted predation rate (sum of male only and minnows only treatments). Hence, there is no evidence for male parental care in L. goodei. In addition, we compared the egg predation rates (filial cannibalism) between males of 3 different color morphs and found no evidence for differential egg cannibalism.     

Male-female Parental Roles in Sarotherodon galilaeus (Pisces: Cichlidae)

Sarotherodon galilaeus is a predominantly biparental, sexually monomorphic mouthbrooder. 15 spawnings of pairs in the weight range 150–450 g were observed in aquaria. Only clutches of females larger than 320 g were reared jointly; with those of smaller females, the first fish to pick up eggs brooded alone, while the comparatively few eggs left for the second fish were invariably eaten. The latency after which eggs were picked up increased with the duration of spawning and indirectly with fish size. This increase was larger in males than in females, so large males started to collect eggs later than their mates. In small pairs (female weight < 200 g), by contrast, the male would pick up eggs first and carry them alone. This is the case in a smaller congeneric species, S. melanotheron, indicating that the apportioning of broodcare is based on a unitary, size-dependent mechanism among Sarotherodon. Yet picking-up order was not entirely determined by these equations. Some fish did not show any reaction towards the eggs and occasionally males became care-givers despite expected longer latency, seemingly because of aggressive dominance.     

The effect of brood size and age on partial filial cannibalism in the scissortail sergeant

Within the size range found in the field for the scissortail sergeant Abudefduf sexfasciatus , there was no correlation between the number of cannibalized eggs and total brood size. Very small broods were fully cannibalized. In a manipulation experiment, males were provided with broods of one of three standardized sizes: at the two extremes and in the middle of the range of naturally occurring broods. Brood size had no effect on partial filial cannibalism, but parental effort increased with increasing brood size. Field correlates and the manipulation experiment showed that the cost of cannibalism in terms of current reproductive success decreased significantly with increasing brood size. Contrary to expectations, there was no relationship between male size and the incidence of cannibalism. No preference for younger eggs was found either from field correlates or from a manipulative experiment in which males were provided with an equal number of young and old eggs at the beginning of the parental phase.     

Filial Cannibalism in the Biparental Fish Cichlasoma nigrofasciatum (Pisces: Cichlidae) in Response to Early Brood Reductions

Filial cannibalism (eating one's own offspring) may enhance a parent's lifetime reproductive success if the costs associated with this behaviour are outweighed by its benefits. An organism might limit its parental care to relatively high quality offspring and eat the others. Or, an organism capable of repeated breeding in the same season might eat the survivors of a brood that was reduced by predators, and breed again. In this study, we manipulated brood size of convict cichlids by removing 0 % (control), 33 % (ER 33) or 66 % (ER 66) of the eggs spawned. The results show that smaller broods are more likely to be cannibalized by their parent(s) than are larger broods. Furthermore, pairs with reduced broods were preparing to respawn; female gonad weights were significantly higher in the brood-reduction groups than in the control group. In a second experiment, we show that the behaviour of the parents differed significantly between experimental groups; the ER 66 group performed less parental care than the control group. Moreover, females invested more parental effort than males. The results suggest that filial cannibalism may be a tactic used by parental convict cichlids to enhance their lifetime reproductive success.     

Underground mating in the fiddler crab Uca tetragonon: the association between female life history traits and male mating tactics

Brood size and other life-history traits of females affect male investment in mating. Female Uca tetragonon, producing relatively small broods, were attracted to the burrows of males for underground mating (UM) while carrying eggs. Most UM females released larvae and ovulated new broods during the pairing, averaging 3.9 days. While a female was incubating one brood, another brood was developing within the ovaries because the females were feeding adequately during incubation. These findings suggest that in U. tetragonon, a small-brood species, females increase the total number of broods produced by breeding continually. In contrast, in large-brood species, feeding by ovigerous females is relatively brief and not enough to prepare the next brood during incubation, inducing temporal separation between incubation and brood production. Unlike females in other ocypodids where females with large broods remain in the breeding burrows of males, most female U. tetragonon left the male after UM. Wandering in female U. tetragonon after the pairs separate may occur because their small broods are adequately protected by an abdominal flap. Relative brood size probably determines the vulnerability of the incubated broods to the females' surface behavior. Hence, male reproductive success in large-brood species may decrease greatly if males expel their mates after ovulation, although this is not necessarily so in small-brood species. Whether the male drives away the female or not may depend on which behavior within either small- or large-brood species yields the greater male reproductive success. In U. tetragonon some females extruded eggs in their own burrows after surface mating as well as in males' burrows after UM. It was unclear whether females chose a male with a larger burrow as an UM mate unlike several large-brood species. Burrows of both UM males and ovigerous females in U. tetragonon were relatively smaller than those in some large-brood species, indicating that incubation of small broods does not require large burrows. Rather than benefits of UM by female choice, wandering resulting from intersexual conflict, and sperm competition may explain why some females mate in males' burrows in this small-brood species.     

Quantifying the benefits and costs of parental care in assassin bugs

1. Which sex should care for offspring depends on the cost and benefits of the behaviour for each sex. Understanding these differences between the sexes is a fundamental step to explain the evolution of animal societies, but it is often difficult to quantify them empirically. A possible approach is to investigate two closely related species that perform a very similar type of care but in which the caring sex differs. 2. Using field and laboratory data, we estimated the benefits and costs of parental care in two species of assassin bugs with very similar ecologies: Rhinocoris tristis, which has exclusive paternal care, and Rhinocoris carmelita, which has exclusive maternal care. 3. In both species, the main benefit of care was a reduction in parasitism and predation of eggs. Guarding R. tristis males consumed eggs (filial cannibalism), and thus managed not to lose weight, but R. carmelita females paid the full energetic cost of care. Guarding male R. tristis incurred survival costs relative to non‐guarding male and female conspecifics. 4. Very high population density and female preference for males already guarding eggs (a preference previously recorded in fish) minimised the promiscuity cost of paternal care in R. tristis, explaining the difference in care pattern between the two species.     

Allopaternal care in the tessellated darter,Etheostoma olmstedi (Pisces: Percidae)

Synopsis Large male tessellated darters, Etheostoma olmstedi, defend flat-bottomed rocks, the undersides of which serve as spawning substrates. Because females attach eggs directly onto bare stone, a spawning bout necessarily decreases the surface area available for further breeding at a nest. In apparent response to the female preference of ovipositing on rocks with the most bare surface, fathers abandon nests with their attached offspring to search for rocks with more uncovered surface. Egg abandonment also results after roving fathers intercept and spawn with ripe females and remain at a different rock to care for a new clutch. In essence, large males appear to maximize the number of eggs they fertilize by sequentially monopolizing breeding patches that are temporarily most desirable to females. The costs to a father of abandoning his eggs appear to be low for two reasons: (1) non-territorial males, created by a scarcity of suitable rocks, readily occupy vacant nests, and clean and aerate the abandoned eggs; and (2) after water hardening, eggs are less vulnerable to cannibalism. The maintenance of eggs by nonparental males may be both incidental to scrubbing the ceiling for their own breeding and adaptive in that viable eggs stimulate females to spawn; neither would appear to involve parental investment costs. Thus, allopaternal care in the tessellated darter may have evolved because it is performed in the selfish pursuit of spawning opportunities while entailing little, if any, of the costs normally subsumed within parental investment.     

ENVIRONMENTAL INFLUENCES ON GROWTH AND SURVIVAL OF NESTLING HOUSE MARTINS DELICHON URBICA

Growth of nestling House Martins was studied in relation to (a) conditions in the external environment and (b) aspects of their breeding biology. The dependence of growth performance on (1) hatchling weights, (2) relative difference in hatchling weights within broods, (3) brood size,(4) season, (5) earliness of breeding in relation to other pairs in the colony, (6) timing of breeding in relation to the median breeding week of the colony and (7) aerial food abundance, was investigated by step-down multiple regression analysis. Up to the stage of the peak brood weight, early laying, small brood sizes and high hatchling weights were associated with higher nestling growth rates. Large relative differences in hatchling weights however tended to depress mean brood weights and increase weight differences (= size hierarchies) within broods. These differences in hatchling weights were considered to contribute significantly to 23% of all nestling deaths, because small, late hatching nestlings suffered very high mortality even when food was abundant. The nestlings which died showed a progressive reduction on growth rates and all succumbed before the 11th nestling day. Because these differences in hatchling weights can be linked to the food supply during laying rather than immediately prior to their death, it is considered that the mortality of these nestlings can ultimately be attributed to the low quality of eggs from which they hatched. There was a tendency for pre-hatching factors to diminish in importance throughout growth, while post-hatching factors increased in importance and, with one exception, were responsible for explaining all the significant variance in the growth characteristics of fledglings. The exception was that differences in wing-lengths in broods could be linked with weight differences at hatching. Food shortages lowered average brood weights prior to fledging. Because pairs breeding during the median breeding week had lighter young, it was inferred that competition for food during this peak of breeding activity had the effect of lowering nestling growth performance, although the overall effect was considered to be small. Early breeding pairs tended to have larger broods, and these large broods showed a lowered growth performance. However, early breeding pairs had relatively smaller weight and wing-length differences, in broods of a given size, than occurred in broods of late breeders. It was therefore concluded that early breeding pairs had some attribute which tended to minimize certain disadvantages of large broods. This effect appeared to be linked to the pair, rather than to season or food supply.     

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract.

• 1 Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.
• 2 First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field.
• 3 In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii.
• 4 In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.
• 5 Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.
• 6 Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

     

Relatively large males lower reproductive success in female zebrafish

Females can adjust their reproductive effort in relation to their partner’s perceived fitness value. In zebrafish (Danio rerio), large males are typically preferred mating partners. However, females have been observed to reduce their reproductive output with exceptionally large males but it remains unknown whether it is due to sexual harassment or aggressive behavior to establish and maintain dominance. Here, we study the association between relative male size, sexual harassment and dominance behavior, female stress status (stress behaviors and whole-body cortisol concentration), and reproductive success during a 4 day spawning trial. We found female cortisol to correlate negatively with female body size and positively with female dominance behavior. However, male and female behavior as well as female cortisol level were not related to relative male size. Females mating with relatively large males produced more and most of their eggs during the first spawning day, while females with smaller males produced few eggs during the first day but then increased egg production. Despite females produced more eggs when mating with relatively larger males, their eggs had substantially lower fertilization rates compared to females mating with relatively smaller males. Hence, overall, the reproductive fitness was lowest when females mated with a relatively large male. These findings could help to explain the maintenance of male size variation under natural conditions.     

Seasonal pattern of filial cannibalism by Apogon doederleini mouthbrooding males

In temperate waters of southern Japan, mouthbrooding males of the cardinal fish Apogon doederleini sometimes ate their entire brood within a day of spawning. In spite of annual variation in age structure and length of the breeding season, however, the annual cannibalism rate (broods cannibalized to total broods spawned) was nearly constant, 12–16%. Fish 1 year old frequently cannibalized early broods of the season, especially the first brood, whereas the cannibalism rate by 2 year-old fish did not vary within the season. In contrast, the cannibalism by older males increased late in the season. This tendency was attributed to their different allocation patterns to growth and reproduction. For 1 year-old fish, which can enhance future reproductive success by growth and cannibalizing on early broods instead of mouthbrooding (at relatively low temperatures), this may be a tactic for investing energy in growth. For fish 3 years, which have more breeding cycles and grow little, cannibalizing late broods may be energetic compensation for their poor somatic condition. No seasonal variation of cannibalism by 2 year-old fish can be explained by their intermediate nature of growth and reproduction. Multiple mate availability is one factor facilitating the cannibalism by 2 and 3 + year-old fish whose operational sex ratio is female-biased.     

Genetic control of geographic variation for cannibalism in the southwestern corn borer,Diatraea grandiosella

The southwestern corn borer,Diatraea grandiosella Dyar, is a subtropical insect whose range has expanded northward within this century. Geographic variation exists between populations at the extremes of the range for a suite of morphological and behavioral characters, including cannibalism. Laboratory colonies established from a Missouri population (37°N lat.) with a high cannibalism rate and a Mexican population (19° N lat.) with a low cannibalism rate were used to examine the genetic basis of cannibalism by means of a controlled breeding design. When larvae were held in pairs on artificial diet in 30 ml plastic cups at 30° C 16L:8D, the highest incidence of cannibalism in both Missouri and Mexican populations was found in larvae 15 to 18 days-of-age (5th and 6th instars). Under these conditions, cannibalism was expressed in 33% of the pairs formed from Missouri larvae and 11% of the pairs formed from Mexican larvae. First and second generation crosses between Missouri and Mexican populations showed an intermediate level of cannibalism, whereas backcrosses to the parental generations showed a regression to the parental phenotypes. These results indicate that cannibalism is under additive genetic control. Larvae from the Missouri parental population were more likely to consume their victim (i.e., cannibalize) once intraspecific killing had occurred than were larvae from the Mexican parental population or from any of the crosses, and female larvae were cannibals more often than were males. Under the conditions employed, no advantage was detected for cannibalism over instraspecific killing for larval weight gain or growth rate.     

Relationship between oocyte morphology and reproductive strategy in loricariid catfishes of the Paraná River, Brazil

Relationships between ovarian structure, oocyte structure/development, and parental care/life history strategies of six loricariid catfishes common in the upper Paraná River, Brazil were examined with analysis of catch data, relative gonad weight, histology, and microscopy. Three life history strategies were observed. Loricariichthys platymetopon , Loricariichthys sp. And Loricaria sp. produce several small clutches of large eggs over a protracted spawning period. Males of these species guard their eggs and larvae, which are transported as a mass on the ventral surface of the male's body. Hypostomus ternetzi and Megalancistrus aculeatus produce the largest mature eggs and the smallest clutches relative to adult mass. The spawning periods of these species are short, and males guard their broods in excavations. Rhinelepis aspera has high fecundity, high relative mass of mature gonads (both sexes), small mature eggs, and broadcast spawning with no parental care. This species migrates to spawn over firm substrates in channel areas during a contracted period. Mature oocytes of external bearers had the thickest zona radiata, followed by the egg scatterer, and cavity nesters. The thickness of the zona radiata probably is an adaptation to protect the developing egg from injury from abrasion. The zona granulosa appeared to be associated with production of secretions responsible for egg adhesion, and this layer was thickest in mature oocytes of the cavity nesting species, followed by the external bearers. All six species have wide distributions in the Paraná River, tributaries, floodplain lagoons, and the Itaipu Reservoir, but brood guarders tended to be most common in lentic habitats.     

FACTORS AFFECTING EGG-WEIGHT, BODY-WEIGHT AND MOULT OF THE WOODPIGEON COLUMBA PALUMBUS

The heaviest clutches (2 eggs) laid by Woodpigeons Columba palumbus in a Cambridgeshire study area weighed 30% more than the lightest. Yet the variation in egg-weight within clutches was less than 1 %. Irrespective of initial weight, eggs lost weight at the same constant rate during incubation. Heavy eggs hatched more successfully than light eggs and none weighing less than 16 g hatched. There was no correlation between chicks' weight at hatching and their weight at day 6 during the July-September part of the breeding season. The ability to feed crop milk at this stage could compensate for low chick-weight, but this might not be true early in the season. Weight at day 6 was correlated with the weight at day 16 or 17. The growth pattern is discussed. Chicks in broods of one achieved a higher weight at day 17 than those in broods of two. The survival rate both in and after leaving the nest was the same in both brood-sizes. Chick-weight in artificially created broods of three was almost as high as in broods of two, but again data refer to the July-September period when abundant cereal food is available. Survival before and after fledging was lower in broods of three. Clutch- and egg-weight declined from April until September. It is suggested that this is adaptive, in that the adults produce heavier eggs when food supplies are most difficult to collect. The critical period probably occurs during the few days when the adult must produce crop milk and the young cannot be left unattended. Thus egg-weight depends on the female's capacity to acquire nutrients, and is related to the needs of embryonic development and the amount of compensation in nutrient supply which can be provided immediately after hatching. But clutch-size is more related to the bird's ability to feed and rear young to the point of fledging, thereby influencing the number of offspring which survive to leave progeny. Egg-weight and female body-weight were positively correlated in females weighing less than 480 g but not in heavier females. First-year birds did not acquire adult weight until midsummer and they would probably produce light eggs if they could breed before this month. However, their gonads do not recrudesce until July and this prevents them breeding in the spring. Seasonal changes in body-weight and fat content of adults and first-year birds are described and discussed; differences were noted between adult males and females which were considered to be adaptive. The moult is described. It begins in April and continues until November, approximately one pair of primaries being replaced per month. The moult ceases during the winter months, when it is known that food supplies become limiting. Woodpigeons lay light eggs relative to their body-weight but can achieve the extra parental care needed for the altricial chicks by producing crop milk. Because the moult is extended, the energy demands of moulting and breeding combined are relatively low and this enables the Woodpigeon to have a long breeding season and to moult coincidentally.