Effects of male presence on agonistic behavior and productivity of White Leghorn hens

We studied the ways in which the presence of a male affects hens' agonistic activity, egg production and body weight. Three experiments were designed involving 18, 16 and 48 flocks with 9–16 females and 0–4 males per flock. Effects of genetic stocks, time elapsed after flock assembly, developmental age, and laying-house environment (cage as opposed to floor) were also examined using factorial experimental designs.Females emitted fewer peck-avoidances and threat-avoidances when one or more males were present; the frequencies decreased with additional males. Pullets in crowded colony cages displayed fewer threats than those in floor-pen flocks, and adolescent pullets displayed more of both kinds of agonistic acts than sexually mature females. Body weight gains and egg weights appeared to be reduced when a male was present within the flock for 30 weeks.     

Floor- and cage-rearing effects on pullets'' initial adaptation to multiple-hen cages

White Leghorn pullets reared in floor pens and high-density cages were compared for behavioral traits and changes in body weights during the initial 2 or 3 weeks after being placed in multiplehen cages during late adolescence. Information on behavior was obtained from 48 pullets kept in 6, 8-bird cages during Days 1, 4 and 15 in Experiment 1, and from 80 pullets kept in 16, 5-bird cages during Days 1 and 7 or 8 in Experiment 2.

In Experiment 1, floor-reared pullets showed significantly more crouching, less movement and lower feed consumption than cage-reared pullets during Day 1. By Day 4, floor-reared pullets still consumed significantly less feed, but by Day 15, no differences were found for crouching, movement or feed eaten. Cage-reared pullets had more feather-pecking on Day 1 but less on Day 15 than floor-reared ones. Pullets from the two rearing environments did not differ in post-housing daily gain in body weight.

In Experiment 2, floor-reared pullets had significantly fewer feeding bouts during Day 1, but they did not differ from cage-reared pullets during Days 7 or 8. Although pullets from floor-pens fed significantly less frequently, they had longer durations of feeding bouts, so that total time feeding did not differ from that of cage-reared pullets. Diurnal feeding patterns changed significantly from Day 1 to Day 7 or 8. Correlation coefficients between measures of individual pullet's feeding behavior and body weight at housing did not differ significantly from zero. Duration of individuals' feeding bouts on Day 7 or 8 was moderately and significantly correlated with their body-weight gain for the first 21 days after housing. Gains in body weight did not differ for pullets from the two rearing treatments.

Most aggressive acts occurred just inside the front of the cages, adjacent to the feed trough; few were seen directly over the feed. Agonistic activity and percentage of dominance relationships known were greater among floor-reared than among cage-reared pullets after transfer to laying-house cages. Decreases in frequency of aggressive acts occurred from Day 1 to Day 7 or 8 for pullets from both rearing environments.     

Plasma prolactin concentrations in breeding pied flycatchers (Ficedula hypoleuca) with an experimentally prolonged brooding period

This experiment explored the stimulatory effect of brooding newly hatched young on plasma prolactin concentration in male and female pied flycatchers, Ficedula hypoleuca. By exchanging offspring between nestboxes, one group of parents was exposed to 1- to 3-day-old nestlings for 12 days. Females in this group continued night-time brooding during these 12 days. The females, but not the males (who do not participate in brooding nestlings), after 6 days had higher plasma prolactin concentrations than control birds which had shown a 50% reduction in night-time brooding at this stage. By Day 12, however, prolactin concentration had decreased to the same level as in control birds, even though these females were still brooding 3-day-old nestlings. Female flycatchers given 3-day-old nestlings on the day their own eggs hatched showed an earlier reduction in night-time brooding and an earlier decrease in plasma prolactin than did control birds. An early decrease in prolactin was also seen in the males of this experimental group.     

Prolonged negative selection of Drosophila melanogaster for a character of adaptive significance disturbs stress reactivity.

The metabolism of juvenile hormone by JH-esterase and JH-epoxide hydrolase, and octopamine by tyrosine decarboxylase were studied under normal and stress conditions in flies of two related lines of D. melanogaster. One was selected for high (HA line) and another for low (LA line) male sexual activity for more than 700 generations. It was demonstrated that prolonged selection for low male sexual activity results in considerable changes in both systems. Tyrosine decarboxylase activity in males and females of the LA line was sharply reduced as compared with those of the HA and control Canton-S lines; JH-esterase and JH-epoxide hydrolase activities were decreased in females, and not in males, of the LA line. It was demonstrated that the response of both metabolic systems to heat stress is impaired in individuals of the LA line: the system of juvenile hormone metabolism does not respond to stress, and that of octopamine metabolism is decelerated. The role of juvenile hormone metabolism in male reproductive function is discussed.     

Social dominance in free-living Willow Tits Parus montanus: determinants and some implications of hierarchy

Several features of social dominance among Willow Tit Parus montanus winter flocks were examined during a four-winter study. Birds of both sexes were evenly distributed over the 33 flocks studied. In nearly half of the flocks there was an adult pair accompanied by yearlings, but one-third of the flocks consisted of more than two adults with yearlings. Males were found to be dominant over and larger than females. Within a sex, yearlings were usually subordinate to adults. The effect of size on dominance, after controlled for sex and age, remained obscure in our field data. The hierarchical status of an individual was found to rise or at least stay the same in different years, which supports the "hopeful dominants" hypothesis, i.e. birds stay in flocks hoping to achieve a higher status in the future. The ranks of mates correlated highly significantly, implying that high-ranking birds were paired with other high-ranking birds and low-ranking birds with other low-ranking birds. Birds of different age and sex did not show any differences in the proportion of initiated aggressive encounters directed at other individuals. However, males were more aggressive to other males than to females and also tended to behave less aggressively towards their own mates than towards other individuals in the flock. This could be a male strategy to strengthen the pair-bond and to enhance mate protection described earlier in     

Enhancing mating performance after juvenile hormone treatment in Anastrepha fraterculus: a differential response in males and females acts as a physiological sexing system

Methoprene (a mimic of juvenile hormone) treatment can reduce the time required for sexual maturation in Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) males under laboratory conditions, supporting its use as a treatment for sterile males within the context of the sterile insect technique (SIT). We evaluated sexual behaviour, mating competitiveness of methoprene-treated males, and female readiness to mate after methoprene-treatment in field cages. The study involved two strains of A. fraterculus from Argentina and Peru, which show several polymorphisms in relation to their sexual behaviour. We also analyzed whether methoprene treatment affected male and/or female behaviour in the same way in these two strains. Methoprene-treated males were equally competitive with untreated mature males, and became sexually competitive 6 days after emergence (3–4 days earlier than untreated males). In contrast, methoprene did not induce sexual maturation in females or, at least, it did not induce a higher rate of mating in 7-day-old females. These results were observed both for the Argentina and the Peru strains. Altogether, our results indicate that methoprene treatment produces sexually competitive males in field cages. In the absence of a genetic sexing system, and when sterile males and females of A. fraterculus are released simultaneously, the fact that females do not respond as do males to the methoprene treatment acts as a physiological sexing effect. Therefore, in the presence of mainly sexually immature sterile females, released sexually mature sterile males would have to disperse in search of wild fertile females, thereby greatly reducing matings among the released sterile insects and thus enhancing sterile insect technique efficiency.     

Reduced blood parasite prevalence with age in the Seychelles Warbler: selective mortality or suppression of infection?

Avian malaria can affect survival and reproduction of their hosts. Two patterns commonly observed in birds are that females have a higher prevalence of malaria than do males and that prevalence decreases with age. The mechanisms behind these patterns remain unclear. However, most studies on blood parasite infections are based on cross-sectional analyses of prevalence, ignoring malaria related mortality and individual changes in infection. Here, we analyse both within-individual changes in malaria prevalence and long-term survival consequences of infection in the Seychelles Warbler (Acrocephalus sechellensis). Adults were less likely to be infected than juveniles but, contrary to broad patterns previously reported in birds, females were less likely to be infected than males. We show by screening individual birds in two subsequent years that the decline with age is a result both of individual suppression of infection and selective mortality. Birds that were infected early in life had a lower survival rate compared to uninfected birds, but among those that survived to be screened twice the proportion of infected birds had also decreased. Uninfected birds did not become infected later in life. Males were found to be more infected than females in this species possibly because, unlike most birds, males are the dispersing sex and the cost of dispersal may have to be traded against immunity. Infected males took longer to suppress their infection than did females. We conclude that these infections are indeed costly, and that age-related patterns in blood parasite prevalence are influenced both by suppression and selective mortality.     

Variation in social rank acquisition influences lifetime reproductive success in black-capped chickadees

Dominance relationships structure many animal societies, yet the process of rank attainment is poorly understood. We investigated acquisition of social dominance in winter flocks and its fitness consequences in male black-capped chickadees (Poecile atricapillus) over a 10-year period. Age was the best predictor of rank, and paired comparisons showed high-ranked males to be older than their low-ranked flock-mates. When controlling for age, morphological variables did not predict male social rank, but high-ranked males were heavier, had lower fat scores and were in leaner condition than low-ranked males. Males that survived between years tended to increase in rank over time; however, the rate of rank advancement varied individually. Rank reversals between familiar contestants were rare, and changes in male social rank were associated with changes in flock membership. Average lifetime reproductive success (LRS) of males and females was variable and best predicted by lifespan. Male rank history also influenced realized reproductive success. Birds with higher average rank over their lifespan were more likely to reproduce successfully. However, among successful birds, average rank did not significantly predict LRS. Thus, birds that lived longer and attained high social rank earlier had higher fitness, but this effect was not manifested as fine-scale differences among successful individuals. Taken together, these findings demonstrate the importance of social factors influencing individual fitness.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 85–95.     

Corpus al latum regulation of copulatory behaviour in the male grasshopper, Melanoplus sanguinipes

Abstract The relationship between corpus allatum (CA) regulation of copulatory behaviour and the CA's influence on the development of the accessory reproductive glands was studied in the male grasshopper, Melanoplus sanguinipes (Fabr.). Allatectomy slowed the development of copulatory behaviour; ≤80% of control males 7 days and older mated with females, but allatectomized males did not show comparable levels of copulation until day 19. In a 3 h observation period, the time taken for 50% of males to initiate copulation was c. 60 min for allatectomized males and only c. 10 min for controls. At the age when 50% of males copulated, the accessory glands of allatectomized males were less developed than those of controls; the accessory gland weight was 65%, soluble protein was 72% and reserves of long hyaline protein I were 40% those of controls. Treatment with Juvenile Hormone III on day 2 stimulated accumulation of long hyaline protein I in 9-day-old allatectomized males to the level found in untreated 19-day-old allactec-tomized males, but did not elicit heightened copulation. No positive feedback from the accessory glands appeared necessary to elicit copulation since vasectomy, ablation of the accessory glands or isolation of the terminal abdominal ganglion by ventral nerve cord transection did not inhibit copulatory behaviour in 7-day-old males. Because allatectomy inhibited copulatory behaviour in 7-day-old males in which the accessory glands were removed but not in 19-day-old males without accessory glands, the increased tendency of older allatectomized males to mate with females was not due to release of inhibition caused by continued growth of the accessory reproductive glands.     

Prolactin and parental behavior in Adélie penguins: effects of absence from nest, incubation length, and nest failure

Adélie penguin (Pygoscelis adeliae) males and females, nesting in Antarctica, alternate attendance at the nest with absences of many days to forage at sea. We investigated the importance of tactile input from egg and chicks on prolactin levels by observing nest attendance patterns and obtaining blood samples (1) during the first nest exchange of the incubation stage, (2) from birds whose incubation period was artificially increased or decreased by about 10 days, and (3) from birds whose nests had failed. Prolactin levels in females after 8 to 11 days of absence from the breeding colony did not differ from those in incubating males and did not change after females resumed incubation. Moving eggs between nests resulted in nests in which chicks hatched after about 26, 36 (normal), or 46 days. Duration of incubation did not affect prolactin levels in the parents measured during incubation, at the pip stage, hatch stage, or early brood stage. Adults first left their chicks unguarded on about the same calendar date, regardless of chick age. However, chicks from long incubation nests averaged 8 days younger when they were left unguarded than chicks from control or short-incubation nests. In females, there was no effect of nest failure on prolactin levels. In males, prolactin levels were slightly lower after nest failure than in males tending nests. Testosterone was significantly higher in males after nest failure than in males still tending nests. Prolactin is elevated in Adélie penguins as part of the program of cyclical hormonal changes that accompany the lengthy reproductive season and is relatively independent of tactile input. Sustained prolactin secretion is probably required for the maintenance of parental behavior in offshore feeding species that must be absent from the nest for many days at a time.     

Space use and agonistic behaviour in relation to sex composition in large flocks of laying hens

Some authors have found indications of subgroup formation when domestic fowl are forced to live together in large flocks, while others have not. In this study experiments were carried out to test the hypothesis that hens in large flocks have home ranges in parts of the pen and that they form subgroups. We also studied if this is influenced by males. In a tiered aviary system (density averaged 16 hens/m(2) of floor area) eight flocks of 568+/-59 ISA Brown laying hybrids were kept in pens. Half of the pens contained 1 male per on average 24 females (mixed flocks). At peak production (36-53 weeks of age) four females roosting closely together for about 14 days and four females roosting far apart from each other were taken out from each flock and put together in separate groups in small pens. Their agonistic behaviour was studied for 2 days before they were put back. This was repeated with new birds, resulting in 16 small sample groups being studied. At 70 weeks, three groups of 10 females per flock roosting closely together in different parts of the pen were dyed with different colours and their locations were observed for 2 nights and 2 days.The incidence of aggressive pecks during day 1 among birds that had been roosting close to each other tended to be lower (P=0.05) than among birds that had been roosting far apart. This effect was not significant among birds from all-female flocks, but among birds from mixed flocks (P<0.05). However, this indicates a recognition of roosting partners and possibly also a rebound effect of the males' reduction of female aggressiveness towards strangers. Irrespective of sex composition in the flocks, birds marked while roosting at the ends of the pens were significantly more often observed within these areas than in other areas of the pen during daytime and came back to the same roosting sites at night (P<0.05-P<0.001). This was not the case for birds from the middle of the pens, where the distribution in the pen in most cases did not differ from random. These results show that laying hens in large groups are rather constant in their use of space, which indicate the presence of home ranges. However, environmental features that facilitate localisation may be important. In summary, we think that these findings indicate the existence of subgroup formation.     

Plasma levels of luteinizing hormone and steroid hormones in free-living winter groups of willow tits (Parus montanus)

Plasma levels of LH, DHT, testosterone, and corticosterone were measured for all members in free-living winter flocks of willow tits, Parus montanus. Hormonal data were related to (1) flock size and (2) age/sex differences. The winter flock defends a large winter territory and shows a well-established social hierarchy in which adults consistently dominate first-year birds. One winter group normally consists of four individuals, two adults and two juveniles. In flocks containing four or five members juvenile willow tits had significantly higher corticosterone values than adults. In small-sized groups, containing three members, all individuals had high plasma levels of corticosterone. No other effects of flock size was found. When data were treated on an age/sex basis, i.e., flock size was not considered, juvenile females were found to have significantly higher plasma levels of testosterone than adult birds, and also significantly higher levels of DHT than juvenile males and adult females. Also, juvenile willow tits had significantly higher plasma levels of corticosterone than adult birds.     

Effects of handling and pair management on reproduction in Japanese quail (Coturnix coturnix )

Three experiments were designed to study the effects of handling, pairing, and frequency of mating opportunities on reproduction in Japanese quail (Coturnix coturnix ) when the sexes were caged separately except during the 90 minute mating periods. In Experiments 1 and 2, 48 females and 48 males were allocated randomly to one of four treatments: 1) continuously paired, 2) paired daily with the same male, 3) paired daily with a different male, and 4) paired every third day with the same male. In Experiment 3, 44 males and 44 females used in Experiments 1 and 2 were again assigned randomly to one of four treatments: 1) continuously paired, 2) paired continuously but the females were handled at the beginning and end of a 90 minute period every third day to simulate the handling associated with moving birds between cages for mating, 3) paired every third day with the same male, and 4) paired every third day with a different male. In Experiments 1 and 3, the females were introduced into the males' cages, while in Experiment 2 males were introduced into the females' cages. In Experiment 1, the females paired every 1 or 3 days with the same males had fewer eggs with embryonic development than continously paired females. In Experiment 2, a reduced number of eggs with embryonic development was observed only in fermales paired every 3 days with the same male. In Experiment 1, more eggs hatched from continuously paired females than from females paired every third day with the same male. In Experiment 3, the females paired every third day with the same males had fewer settable, developing, or hatching eggs. In conclusion, it was found that when the sexes need to be caged separately, it is better to expose the females to different males.     

Genetic similarity, extrapair paternity, and offspring quality in Savannah sparrows (Passerculus sandwichensis)

The occurrence of extrapair paternity (EPP) in birds is oftenattributed to the action of good-genes sexual selection wherebyfemales "trade up" on male genetic quality by allocating fertilizationsto males with better genes than those possessed by their socialmate. To date, most studies of EPP in birds focus on absolutemeasures of male quality as a criterion for female choice, althoughmultiple mating by females in other taxa is more commonly ascribedto benefits associated with the individual optimization of offspringgenotypes. Here, we examine whether the genetic similarity ofsocial mates predicts female mating patterns in a populationof Savannah sparrows (Passerculus sandwichensis) where as manyas 70% of adults produce extrapair young (EPY). We considerthe influence of genetic similarity across all stages of a female'sdecision-making process, from pair formation through the decisionto produce EPY, to the allocation of fertilizations to specificextrapair sires. In a 4-year study of 175 males, 206 females,and 506 offspring, females were more likely to produce EPY whenpaired to genetically similar males, but they did not appearto be influenced by the size, age, mass, individual heterozygosity,and genetic diversity of their social mates. In paired comparisons,females were almost twice as likely to decrease their geneticsimilarity to males when producing EPY as they were to increaseit. Nonetheless, females did not select especially dissimilarmales when mating outside the pair-bond nor did they pair disassortativelywith respect to genetic similarity. Relative measures of malequality may influence mating patterns in birds, but only atsome points in a female's decision-making process.     

IgG and IgM responses in high and low antibody-selected lines of chickens

Kinetics of IgG and IgM as measured by 2-mercaptoethanol-resistant (MER) and susceptible (MES) antibodies to sheep erythrocytes, respectively, were determined as correlated responses in lines of chickens selected for high (HA) and low (LA) antibody response to sheep erythrocytes. Primary response patterns for total, MER, and MES antibody differed according to the genetic line. Total antibody increased rapidly, peaked, and persisted at moderate levels in line HA, whereas both peak and persistency were lower in line LA. Levels of MES peaked and then declined in line HA chickens but persisted at low levels throughout in line LA. Titers of MER antibody were considerably greater in line HA than in line LA both on an absolute basis and as a proportion of total antibody titer. Secondary total titers were greater at five days after injection than at three days and greater for line HA than for line LA chicks. The pattern observed for MER and MES in line LA was similar to that for total antibody, as was MER in line HA. For MES the pattern was reversed in line HA.     

Methoprene-induced matings of young Queensland fruit fly males are effective at inducing sexual inhibition in females

Pre-release dietary treatment with methoprene, a juvenile hormone analogue, decreases the age at which male Queensland fruit flies mature and hence may decrease the post-release delay until released sterile flies participate in sterile insect technique (SIT) programmes. However, if matings of young methoprene-treated males are not effective at inducing sexual inhibition in their mates, then this treatment may not enhance SIT. The present study investigates efficacy of matings of methoprene-treated males at inducing sexual inhibition in their mates. Methoprene incorporated into a diet of sugar and yeast hydrolysate (w/w 3:1) for 48 hr after emergence resulted in significantly increased male mating propensity when flies were <10 days of age, but not when older, and longer copulations. Copula latency did not vary with methoprene treatment but did decrease with age. The matings of young methoprene-treated males were effective at inducing sexual inhibition in their mates, matching the efficacy of untreated mature males. Regardless of treatment, females had reduced tendency to remate if their first mate was 15 days of age than if their first mate was younger (6, 8 days) or older (20, 25, 30 days). Females mated by methoprene-treated males that did remate tended to remate later in the day than females mated by untreated males. Also, second copula durations of females first mated by a 6- to 10-day-old male were shorter if the male was methoprene treated. These patterns in remating females may indicate greater efficacy of the initial mating of methoprene-treated males. Overall, we find that the additional matings of young methoprene-treated male Queensland fruit flies are effective at inducing sexual inhibition in their mates. This finding supports the incorporation of methoprene into pre-release diet for SIT.     

Variation in numbers, territoriality and flock size of a Goldcrest Regulus regulus population in winter

A Goldcrest Regulus regulus population living in a spruce-dominated forest near Oslo (c.60°N), in southern Norway, was studied during the winters (November-March) from 1966–67 to 1971–72. A significant reduction in population size occurred between November and March, the recorded values varying from 76 to 96%, with a mean reduction for all six winters studied of 86%. This winter decline in numbers was significantly correlated with both precipitation (i.e., snowfall) and ambient temperature, but not with bird density. Spiders were the predominant prey items of the Goldcrests, and it is suggested that the birds experience food shortages that affect their survival rate. Although not statistically significant, a mean change in the ratio of males:females from 2:1 in October-November to 10:1 in December—February was observed, suggesting that a greater mortality of females than males occurs during the winter.
Partly based on data for colour-banded birds, it is suggested that the Goldcrests form social flocks, which move around as individual units within territories of about 9 ha (7.5 12 ha, n = 5) in extent. The mean flock size decreased significantly from 4.57 ( n = 157) birds in November-December to 2.82 ( n = 74) birds in January-February, probably because of the reductions in the size of the local population during the winter. The mean flock size in November-December varied inversely with the ambient temperature ( r = -0.92).     

Slow continuous wing-moult of Zebra Finches Poephila guttata from southeast Australia

Moult of the remiges was studied over eight years in a population of Zebra Finches from southeast Australia. In first-year birds the first primary was lost at mean age of 80 days in both sexes; moult took 204 days to complete in males and 223 in females. Birds hatched in autumn postponed the start of their primary moult until spring. Primaries were replaced slowly in a rigid, non-overlapping, ascending order from #1 to #9 but the secondaries did not display a rigid sequence.
Adult Zebra Finches moulted remiges throughout the year. Primary moult was initiated in any month. Primary moult had a mean duration of 229 days for males and 240 days for females. Primaries moulted in continuous waves: the interval between successive moults in males was –16 days and +6 days in females. Limited food, low temperatures and breeding slowed, but did not stop, wing-moult. Birds caring for eggs and young actively replaced remiges.
The pattern of wing-moult displayed here by Zebra Finches is exceptional for passerines and may be related to the opportunistic breeding strategy necessary in an arid, unpredictable environment. Its presence in the Victorian birds may be non-adaptive.     

Reproductive performance of rhesus macaques (Macaca mulatta) in two outdoor housing conditions

This study examined the reproductive performance of rhesus macaques maintained in two different housing conditions: high-density semi-sheltered gang cages and low-density outdoor corrals. Two hundred sixteen subjects were housed in 49 gang cages, each of which contained one breeding male and between one and eight breeding females. Two hundred seven subjects were housed in 13 corrals, each of which contained between two and four breeding males and between 9 and 26 breeding females. Over a 3-year period, pregnancy, live birth, and production rates were significantly greater for females in corrals than for females in gang cages. Fetal death rate was lower in corrals than in gang cages, while neonatal death rates did not differ between housing conditions. These differences did not result from potential confounds such as differential age structures or virological statuses between housing conditions. We conclude that, for rhesus macaques, outdoor corral housing leads to better reproductive performance than does semi-sheltered gang housing, probably as a result of increased individual space and relaxation of intense social stressors.