Termination of incubation in doves: Influence of egg fertility and absence of mate

The present experiments examine the role of the eggs, the mate, and hormonal state in the termination of incubation by ring doves. Doves given either infertile eggs or newly laid fertile eggs at midincubation did not prolong incubation significantly beyond that observed in doves with hatching eggs. However, there was substantial lack of synchrony between mates in the experimental groups. Half the experimental females laid new eggs, often without interrupting incubation. To clarify the role of the mate in maintaining sitting, pairs were separated on Days 1, 5, or 10 of incubation. Initially birds in each group incubated alone throughout the day. The decline in sitting was more rapid in pairs which had been separated early in incubation. To explore the hormonal correlates of the termination of incubation, mates were separated on the 10th day of incubation and observed until they quit sitting. At this time, males showed substantial crop development. Females had little crop development and large preovulatory folliclels, indicating readiness to lay new eggs despite the absence of the male. We conclude that the termination of incubation by parent doves is delayed by the presence of the mate and this, in turn, prevents follicular development and recycling by the female. Cues from the offspring are important in synchronizing the behavior of the parents and also in preventing a new breeding cycle.     

External factors affecting the duration of broody behavior in the ring dove (Streptopelia risoria)

The object of this study was to investigate factors which determine the duration of sitting in ring doves. This normally lasts ca. 19 days from laying, with very small variation. The period is made up of 15 days incubating eggs and 4-5 days brooding squabs. The duration of sitting is unaffected by substituting fresh or sterile eggs, and can only be slightly influenced by substituting foster squabs or new eggs just before or after hatching. The sitting period appears to be predetermined to run for 19 days following laying. The maintenance of sitting, however, requires the presence of the nest and eggs, and can be drastically varied by keeping subjects in continuous daylight or on a day of 6 hr light:6 hr dark (6 L:6 D). Birds kept on ahemeral cycles (11 L: 10 D; 13 L:14 D) displayed significantly different periods of incubation on infertile eggs and recycling, indicative of an endogenous circadian basis to the timing mechanism.     

Gonadal and hormonal characteristics of captive adult mourning doves during the nesting cycle

Paired mourning doves ($\text{Zenaida}$$\text{macroura}$) of a captive breeding colony were selected and sacrificed on specific day intervals postlaying and posthatching during 1976–1977. Blood plasma samples were analyzed for androgens, estradiol, and progestins using radioimmunoassays. Testes, ovary and oviduct weights, spermatozoan numbers, diameter of the three largest follicles in the ovary, the presence or absence of eggs in the reproductive tract, and crop gland characteristics also were recorded. Differences (P<0.05) existed between nonbreeding and breeding pairs in testes weights, spermatozoan numbers, and ovary and oviduct weights. No distinct cyclic pattern was observed in gonadal variables among breeding males and females during the nesting cycle, although trends were observed. No differences (P > 0.05) in androgen and progestin concentrations in males, or estradiol and progestin concentrations in females, between nonbreeding and breeding pairs, or among breeding pairs during different stages of the nesting cycle, were observed. Analysis of reproductive variables by stage of crop gland activity tended to indicate an inverse relationship between gonadal and crop gland activity in both male and female doves during the nesting cycle.     

Plasma luteinizing hormone during the breeding cycle of the female ring dove

Plasma luteinizing hormone (LH) levels in serial blood samples of female ring doves (Streptopelia risoria) were measured by radioimmunoassay method. Our findings indicate the following pattern of LH levels: LH increases during early courtship which reaches a peak (5.43 ± 0.79 ng/ml) during the nesting period. LH declines following egg-laying (3.77 ± 0.33 ng/ml) and again after hatching (2.23 ± 0.28 ng/ml). It remains high in females which laid infertile eggs initially and subsequently showed a further laying. The results are compared with published data on plasma estrogens and progesterone in the dove's breeding cycle.     

4. UNUSUAL EXPERIENCES WITH BIRDS

Earlé, R. A. 1989. Breeding biology of the Redbreasted Swallow Hirundo semirufa. Ostrich 60: 13–21.

The two races of the Redbreasted Swallow Hirundo semirufa seem to have separate breeding seasons with the northern race H. s. gordoni breeding April-July, while most records for the nominate race fall in October-February. All nests studied were in concrete culverts less than 1 m high. Eggs laid in second clutches by individual females weighed significantly less than eggs laid in first clutches. Eggs hatched on average 16,2 days after incubation started or 18–21 days after the eggs were laid. Only females incubated. Chicks fledged 23–25 days after hatching and reached a maximum body mass of about 31,5 g on day 18 before a steady decline in mass until fledging. Most nesting failures resulted from infertile eggs or starvation of young in the nest (16,2% of all young starved). Overall breeding success was 60,6%. In all, 81,8% of first clutches produced fledglings but only 44,4% of second clutches. Over a three year period 4,9 young were produced per pair breeding in the area (1,6 young/pair/breeding season).     

Consequences of a female-biased sex-ratio in a socially monogamous bird: female-female pairs in the Roseate Tern Sterna dougallii

In the socially monogamous gulls and terns, female-biased sex ratios are sometimes revealed by the occurrence of ‘supernormal clutches’, which are usually attended by female-female pairs or other multi-female associations. We studied these phenomena in the endangered Roseate Tern Sterna dougallii at Bird Island, USA, from 1970 to 1995. DNA-techniques were used to sex breeding adults in 1992–94. Supernormal clutches (with three or four eggs) have comprised 1–7% of all Roseate Tern clutches at Bird Island since at least 1970, probably increasing in frequency since 1980. Supernormal clutches were spatially clustered; most were laid late in the peak period of nesting during each season. More than 80% of supernormal clutches and at least 7% of normal clutches were attended by multi-female associations; most of these were female-female pairs, with a few trios (male + two females, or three females) and one quartet (four females). More than half of the multi-female associations attended normal clutches. Some female-female pairs were maintained for up to five years. The age-distribution of females mated to females did not differ significantly from that of females mated to males. Females mated together usually laid eggs synchronously (±2 days). Such females laid fewer eggs than females mated to males (means 1.20 versus 1.73), and had lower fertility and hatching success (about 46% versus 98%); they were less successful in raising young from eggs that did hatch (means 58% versus 73%), but this difference was not significant. Their overall breeding success was much lower (about 0.34 fledglings per female versus 1.35). The sex-ratio of breeders was about 127 females to 100 males; about 20% of breeding females did not have male mates. Female Roseate Terns that do not obtain male mates appear to be of low phenotypic ‘quality’ - based on late laying, small clutches and small eggs. Our data support the hypothesis that such females have a higher fitness if they mate with each other and raise a few young than if they do not breed at all.     

Hypothalamic monoamine turnover in ring doves (streptopelia risoria), courting,incubating and brooding young

1. The turnovers of hypothalamic 5-hydroxytryptamine (5HT), dopamine (DA) and noradrenaline (NE) were measured in male and female ring doves (Streptopelia risoria) at three stages of the breeding cycle: courtship, 3 days after pairing; early incubation, 1–2 days after egg laying; and brooding, 1–3 days after the squabs had hatched.2. In both sexes plasma LH decreased progressively from courtship through incubation to brooding young. Crop sacs were fully developed in doves brooding young but not at other stages of the reproductive cycle, indicating increased concentrations of plasma prolactin.3. The turnovers of 5HT and DA in both sexes were significantly higher (P<0.001) in doves brooding young than in birds incubating eggs or nest building. The turnover of DA was higher in females than in males at the onset of incubation. The turnover of NE was lower (P > 0.01) in females at the onset of incubation than during courtship or brooding.4. Increased turnover of hypothalamic DA may be more closely related to brooding behaviour than to changes in prolactin or LH secretion.5. Increased hypothalamic 5HT turnover in brooding doves appears to be more directly related to crop sac development, and by inference increased prolactin secretion, than to depressed plasma LH concentrations.     

Gonadal hormones determine sex differences in timing of incubation by doves.

Male and female ring doves express a sexually dimorphic pattern of incubation. The dimorphism is temporal rather than motoric. The male incubates for a block of time in the middle of the day and the female incubates the rest of the time. The present study explored the role of gonadal hormones in the control of the temporal dimorphism. Female-female pairs incubated their eggs, but it could not be predicted which of the partners would be sitting on the nest at any given time. Male-male pairs did not incubate and instead destroyed the nests that were provided and displayed aggressive behavior. Some intact males incubated when paired with gonadectomized males, although the castrates tended to ignore the nest. In contrast, when castrated birds were given heterotypical hormonal replacement therapy, they and their same-sex partners incubated the eggs that had been provided, with the gonadectomized birds sitting at a time appropriate to the hormonal state. The results indicate that gonadal hormones influence not only the expression of incubation behavior, but also its phase and duration.     

Oviposition of fertile eggs and postponement of subsequent egg laying in ring doves (Streptopelia risoria).

Within the 45 days after an oviposition, fewer female doves which had laid fertile eggs laid a subsequent clutch than did females which had laid infertile eggs. During incubation the fertile eggs were replaced by infertile ones; therefore, this difference was not a result of raising squabs.     

Androgen and behavior in the male three-spined stickleback,Gasterosteus aculeatus. II. Castration and 11-ketoandrostenedione effects on courtship and parental care during the nesting cycle

Courtship declines and ceases while parental care increases in the presence of developing eggs during the nesting cycle of the male three-spined stickleback, Gasterosteus aculeatus. Furthermore, circulating 11-ketotestosterone (11KT) levels are higher during the initial "courtship phase" than during the later "parental phase," similar to that found in other paternal fishes. This study aimed to investigate a possible functional relationship between changes in 11KT levels and changes in reproductive behavior during the nesting cycle. To this end, groups of nonspawned and spawned male sticklebacks were sham-operated, castrated, or castrated and treated with 11-ketoandrostenedione (11KA), and the effects of the treatments on courtship and parental care were studied. Castration removed circulating 11KT, while 11KA replacement prevented the natural decline in 11KT during the parental phase (11KA converts to 11KT extratesticularly), as assessed by radioimmunoassay. Regardless of treatment, parental care remained low and courtship was present in all nonspawned males, even at the end of the experiment. However, courtship did eventually decline in castrated nonspawned males compared to the other two nonspawned groups. In all treatments of spawned males there was a drastic decline in courtship and an increase in parental care. In castrated spawned males, however, the decline in courtship came earlier than in the other two spawned groups. 11KA treatment did not prevent the natural decline in courtship/increase in parental care in spawned males, indicating that the natural decline in 11KT is not responsible for the main portion of the rapid changes in these behaviors over the stickleback's nesting cycle. The limited effects of castration also exclude other gonadal hormones from being responsible for most of these changes.     

Persistency of broodiness in recycled turkey hens

Large White turkey breeder hens identified as broody during their initial egg production cycle were recycled into a second and third reproductive cycle in order to determine the persistency of broodiness. Egg production data included time to first egg, duration of lay and the number of eggs per hen. Nesting data included time to first broody nesting activity and duration of broody nesting activity. In general, there were no significant differences among the three cycles for the above observations. Mean values over the three cucles were as follows: 24.6 days to first egg following photostimulation; 49.4 days of egg production; 29.4 eggs per hen; 46.9 days from the first egg to first broody nesting and 59.7 days duration of nesting. Of 10 hens identified as broody in their first egg production cycle and followed through two additional 20-week cycles, seven hens demonstrated broody nesting behavior and nine had low rates of egg production. It was concluded that broody traits of a given hen are carried over into subsequent cycles.     

The transition from sitting on eggs to sitting on young in ring doves, Streptopelia risoria: squab-egg preferences during the normal cycle.

Ring doves of both sexes sit on young squabs after hatching in much the same manner as they sit on eggs before hatching, but this study demonstrates that the preferred stimulus varies with the state of the animal. A simultaneous, squab-egg choice test was given on days 1, 4, 10, and 13 of incubation and on the day following hatching in normal reproductive cycles of experienced and naïve male and female ring doves. Naïve doves were more likely than experienced doves to choose eggs throughout the cycle (P<0·005) and, overall, eggs were more likely to be chosen during early incubation and squabs posthatching (P<0·005).     

Mate Choice and Mating Pattern in a Stream Goby of the Genus Rhinogobius

The mate choice and mating pattern of a benthic goby Rhinogobius sp. CB (cross band type) were investigated in the Kamo River, Shikoku, Japan. During the breeding season, gravid females assumed a nuptial color and either males or females initiated a courtship display. Males preferentially courted a female of similar size to lead her to his nest, whereas females courted more frequently when they encountered a large male. Eggs in any one nest were always at the same developmental stage. Sampling data of nesting males and females indicated that, in more than half the nests, males gathered more than one female before spawning. In some nests with eggs, two or three females had spent ovaries, indicating that the eggs were laid by multiple females within a short span of time. However, a comparison between the total number of eggs which females would spawn in one nest and the number of eggs actually deposited suggested that eggs were contributed by one female in most nests. This low level of polygyny in spite of multiple female availability is attributed to a limited available spawning area of the nest.     

Effects of stimuli emanating from the nest on the reproductive cycle in the ring dove. I: Pre-laying behaviour

The course of several behavioural patterns could be influenced by controlling the state of the nest available to a pair of ring doves (Streptopelia risoria). These patterns were: wing-flipping, handling of nesting material, nest bowl occupancy, and nervous activities. In groups having to build nests, the onset of wing-flipping by the female occurred at a predictable time before egg-laying. It is argued that during nest-building a female influences the male to carry material to her by sitting in the nest bowl and wing-flipping. In pairs provided with a completed nest, the course of the pre-laying cycle was changed and the ‘typical’ sex roles did not emerge. The relationships between the male and female are discussed.     

Females of a blood-sucking bug may adjust their mating decisions according to the risk of ovipositing infertile eggs

Females should adjust their mating preferences when the costs of being selective vary. Here, we focus on the cost of laying unfertilized eggs. Oviparous species lose their fertilizable oocytes if remain virgin for too long. Thus, females who are at a high risk of laying infertile eggs should be selected against rejecting a mating opportunity under such circumstances. We test this prediction using the blood-sucking bug Rhodnius prolixus females, which exhibit stereotyped discrimination behaviour to undesired copula. Under laboratory conditions, we compared the copulatory rejection behaviour between females at their first ovarian cycle (12 days old adults, at low risk of ovipositing infertile eggs) and females at their second ovarian cycle (26 days old adults, at high risk of ovipositing infertile eggs). Since R. prolixus female rejection behaviour is mainly exhibited in the presence of potential mates, we also manipulated the presence and absence of additional males. We found that rejection behaviour significantly decreases both when females enter their second ovarian cycle (and are at high risk of losing unfertilized eggs) and under the absence of additional males. We discuss the possible effects of the risk of losing fertilizable eggs on female mating preferences.     

Contributions of reproductive experience to observation-maintained crop growth and incubation in male and female ring doves

Previous work has established that experienced male ring doves (Streptopelia risoria) can maintain prolactin-dependent crop growth and readiness to incubate by observing an incubating partner. We report that this is also true for female ring doves. The role of experience in this phenomenon was examined in separate experiments with males and females. Observation of an incubating mate from 3 days after completion of egg laying is sufficient to maintain crop growth and incubation in both male and female ring doves in their second, but not in their first, reproductive cycle. Male and female doves in their first cycle must incubate for a greater part of the cycle before observation of an incubating mate is an effective stimulus; there are no differences between first and second cycle doves separated by a glass plate from the mate and nest 8 days after laying. Experience obtained within the first cycle apparently ensures that previously neutral stimuli come to elicit prolactin secretion. The effectiveness of these stimuli is reinstated early in a second cycle.     

The fungicide methyl 2-benzimidazole carbamate causes infertility in male Sprague-Dawley rats

A serial breeding technique was used to evaluate the fertility of male Sprague-Dawley rats after exposure to the fungicide carbendazim (methyl 2-benzimidazole carbamate). Proven-fertile male rats (90 days old) received 10 daily doses of corn oil or carbendazim (400 mg/kg/day) peroral. Each male was bred with a new female each week; breeding began on the third day of treatment and continued for 32 wk after the last day of chemical exposure. Twelve days after each breeding period, the females were killed, their uteri were examined for resorptions, and the number of dead and viable fetuses was determined. All males were killed 35 wk post exposure, and testicular tissue was prepared for histopathological examination by vascular perfusion. Fertility (percent fertile as indicated by pregnant females) of males in the carbendazim-treated group was depressed the first post-exposure week; 10 of the 24 treated males failed to produce a pregnant female as compared with no failures in the control group. By the fifth post-exposure week, 16 of the 24 carbendazim-treated males were infertile. Of these 16 males, 4 recovered fertility after a failure to produce a pregnant female for 5-11 consecutive breeding periods. However, 12 of the males did not recover fertility during the remainder of the 32-wk post-exposure period. Histological examinations of testicular sections 245 days post exposure revealed that exposure to carbendazim caused severe seminiferous tubular atrophy (greater than 85% of tubules were atrophic) in those carbendazim-treated males that failed to recover fertility.(ABSTRACT TRUNCATED AT 250 WORDS)     

THE BIOLOGY OF THE WAVED ALBATROSS DIOMEDEA IRRORATA OF HOOD ISLAND, GALAPAGOS

As a nesting species, the Waved Albatross Diomedea irrorata is restricted to Hood Island in the Galapagos archipelago where 12,000 pairs bred in 1971. Outside the islands the species occurs over the northern parts of the Humboldt Current. Two colonies were studied in detail (1970–1971). At the start of a season, males returned first to the colonies and defended a small territory. Copulation occurred without any elaborate ceremony and the female spent little time on land before laying. There was no fixed nest-site, even within a season, and birds moved their eggs considerable distances. This resulted in heavy egg losses. Younger birds bred later than older birds and laid longer but narrower eggs. The average incubation spell varied from four to five days at the extremes of the incubation period to 19 days in the middle. The average incubation and fledging periods were 60 and 167 days respectively. Pairs which lost an egg sometimes adopted the abandoned egg of another bird and successfully reared the chick. Most pairs nested in both seasons. Nesting success was extremely variable, both between years and between colonies. Between 1961 and 1971 at Punta Suarez, virtually no young were reared in four seasons. Even in 1970–71, where nesting success was good, some groups of birds deserted their eggs en masse whereas in neighbouring areas up to 80% of the pairs reared young. The main foods of the young were squid and fish. Birds did not moult wing and tail feathers at the breeding colonies, and about 50% retained some primaries for more than one season, suggesting that successful pairs had difficulty in fitting in a complete moult between breeding attempts. Old feathers were normally found among the inner primaries and at the next moult were preferentially replaced, though adjacent newer feathers were sometimes retained for another season. Some birds bred in their fourth years, but most not until a year or two older. Immatures were present at the colonies late in the breeding cycle, the youngest returning latest and remaining until the last young fledged. Survival of adults and young averaged at least 95% and 93% per annum over many years. Adults and young ringed in 1961 survived equally well. The significance of the timing of the return of immatures and of the large-scale desertion of eggs, apparently not due to food shortage or disturbance, is discussed.     

Temporal changes in the migration phenology of turtle doves Streptopelia turtur in Britain, based on sightings from coastal bird observatories

Using daily counts of birds seen at six coastal bird observatories in southern and eastern England, we explored the migration phenology of turtle doves during the period 1963 to 2000. Annual totals increased threefold up to the late 1970s then decreased again, in accordance with the BTO Common Birds Census (CBC) index of abundance. Median annual spring arrival and autumn departure dates of turtle doves were not related to abundance (CBC index) or mean temperature in spring or summer respectively. Although median annual spring arrival date has not altered over the 38-year period, median annual autumn departure date has become earlier by 8 days. This has resulted in a shortening of the breeding season by 12 days, which ties in with a reduction in average number of nesting attempts per pair observed by a recent autecological study. It is possible that breeding turtle doves are now out of phase with peaks in food availability. This may have resulted in reduced breeding performance and earlier termination of the breeding season, and may have partly contributed to the decline of the species.     

Polygyny and the breeding success of the great reed warblerAcrocephalus arundinaceus

Settlement date, mating status, and breeding success of individually marked great reed warblers, Acrocephalus arundinaceus, were studied during the 1980–84 breeding seasons in Kahokugata, Ishikawa Prefecture, Japan. Twenty-five per cent of the territorial males were polygynous, of which the majority were bigamous. The settling periods of both sexes were long, extending for 65 days in males and 49 days in females. About 80% of males and females settled in the first half of the settling period, and the settlement date of 28–54% males overlapped with that of females. Many of the late settlers were bachelors and the males which mated earlier tended to be polygynous. The timing of a male's settlement is important in acquiring mates. Fifty-five per cent of eggs laid were lost before fledging, mainly due to predation. The mean number of fledglings was 3.19 per primary female, 2.41 per secondary female, and 2.80 per monogamous female. Comparison of the number of fledglings of females which mated during the same period showed that the presence of another female in the same territory did not adversely affect the breeding success of either of the polygynous females. Polygynous males have the advantage of decreasing the risk of breeding failure under high predation pressure.