Are incubation costs in female pied flycatchers expressed in humoral immune responsiveness or breeding success?

Although clutch size variation has been a key target for studies of avian life history theory, most empirical work has only focused on the ability of parents to raise their altricial young. In this study, we test the hypothesis that costs incurred during incubation may be an additional factor constraining clutch size in altricial birds. In the pied flycatcher (Ficedula hypoleuca), we manipulated the incubation effort of the female by enlarging and reducing clutch sizes. To manipulate incubation effort only, the original clutch sizes were restored shortly after hatching. We found that fledging success was lower among broods whose clutches were enlarged during incubation. There was, however, no effect of manipulation on female body condition or on their ability to mount a humoral immune response to diphtheria or tetanus toxoid during the incubation or nestling provisioning period. Instead, we found that the original clutch size was related to the immune response so that females with seven eggs had significantly lower primary antibody responses against tetanus compared to those with six eggs. Our results suggest that incubating females are not willing to jeopardise their own condition and immune function, but instead pay the costs of incubating a larger clutch by lower offspring production. The results support the view that costs of producing and incubating eggs may be substantial and hence that these costs are likely to contribute to shaping the optimal clutch size in altricial birds.     

Division of labour during incubation in a woodpecker Colaptes auratus with reversed sex roles and facultative polyandry

The contribution of males to incubation has rarely been studied in altricial birds because the pursuit of extra mating opportunities is believed to conflict with incubation. Woodpeckers show reversed sex roles in parental care with males doing most of the nest construction, incubating and brooding of the young while females may be polyandrous. I investigated incubation by each sex at 71 monogamous and four polyandrous nests of the Northern Flicker Colaptes auratus , predicting that males would contribute to incubation according to their energy reserves (body condition) whereas females would contribute based on alternate reproductive opportunities. Nest attendance was 99% with males contributing a mean of 66% of the total incubation including nocturnal incubation. The length of daytime bouts averaged about 2 h and did not differ between the sexes. Consistent with predictions of investment strategies, structurally larger males and those in poorer body condition incubated less than smaller males, perhaps because they required more recess time to forage or to conserve energy. Older females contributed less incubation than young females and polyandrous females contributed less incubation at their secondary nests than monogamous females. Incubation period, nest depredation rate and hatching success were not influenced by bout length, number of bouts or relative contribution of the sexes. Hatching success was 86% at nests of both monogamous and polyandrous females because males compensated for reduced female participation. Because incubation of the sexes is compensatory and not additive, incubation pattern did not influence short-term reproductive success. I conclude that males invest in incubation according to their energy needs, and females may adjust their contributions based on alternate reproductive tactics.     

Hatching asynchrony and brood reduction influence immune response in Common Kestrel Falco tinnunculus nestlings

The onset of incubation before the end of laying imposes asynchrony at hatching and, therefore, a size hierarchy in the brood. It has been argued that hatching asynchrony might be a strategy to improve reproductive output in terms of quality or quantity of offspring. However, little is known about the mediating effect of hatching asynchrony on offspring quality when brood reduction occurs. Here, we investigate the relationship between phenotypic quality and hatching asynchrony in Common Kestrel Falco tinnunculus nestlings in Spain. Hatching asynchrony did not increase breeding success or nestling quality. Furthermore, hatching asynchrony and brood reduction had different effects on nestlings’ phytohaematogglutinin (PHA)‐mediated immune response and nestling growth. In asynchronous and reduced broods (in which at least one nestling died), nestlings showed a stronger PHA‐mediated immune response and tended to have a smaller body size compared with nestlings raised in synchronous and reduced broods. When brood reduction occurred in broods hatched synchronously, there was no effect on nestling size, but nestlings had a relatively poor PHA‐mediated immune response compared with nestlings raised in asynchronous and reduced broods. We suggest that resources for growth can be directed to immune function only in asynchronously hatched broods, resulting in improved nestling quality, as suggested by their immune response. We also found that males produced a greater PHA‐mediated immune response than females only in brood‐reduced nests without any effect on nestling size or condition, suggesting that females may trade off immune activities and body condition, size or weight. Overall, our results suggest that hatching pattern and brood reduction may mediate resource allocation to different fitness traits. They also highlight that the resolution of immune‐related trade‐offs when brood reduction occurs may differ between male and female nestlings.     

The cost of incubation in relation to clutch-size in the Collared Flycatcher Ficedula albicollis

This study examines the importance of avian incubation costs as determinants of clutch-size variation by performing clutch-size and brood-size manipulations in the same population of Collared Flycatchers Ficedula albicollis during the same breeding season. In 2 5 cases when three or more clutches of the same size were completed on the same day, we moved two eggs on the day after the last egg had been laid from one randomly selected clutch (C) to another (C) and moved two other eggs from this to a third clutch (C⁺). In 20 other cases of simultaneously completed clutches of the same size, we moved two randomly selected young from one brood to a second and from that moved two other young to a third (B, B and B⁺groups). Most females were weighed the day after completion of the clutch and 1–4 days before hatching of the young, and some of them also 10–14 days after hatching of the young. We measured the daily energy expenditure of females incubating manipulated clutches of 4, 6 and 8 eggs by means of the doubly-labelled water (D₂¹⁸O) technique and also recorded their nest attendance. Hatching success of fertilized eggs was reduced in the enlarged clutches compared with control and reduced clutches. Females expired on average 3142.6 ml CO₂ and expended 78.6 kJ per day while incubating, which corresponds to a metabolic intensity of 3.3 times BMR. Daily energy expenditure increased with clutch-size due to higher costs while incubating, and not because of changed activity patterns. There were no significant differences in length of incubation, female mass or mass changes between phases for the C, C and C⁺groups. In both the C and B groups, enlarged broods produced significantly more fledged young than control broods, and those significantly more than reduced broods. Fledgling tarsus-length and mass did not differ significantly between treatments in either the C or B groups. There was no significant difference in breeding success between clutch and brood manipulations. In this season, incubation costs did not entail significant fitness losses, expressed either as fledgling production or female condition. Also, control females could have raised more young to fledging age than they did with no apparent costs.     

Behavioral responses of nesting female dark‐eyed juncos Junco hyemalis to hetero‐ and conspecific passerine preen oils

Several studies have suggested a greater role for olfactory cues in avian social interactions than previously recognized, but few have explicitly investigated the effect of odor on parental behavior. We present results from a preliminary study in which we applied hetero‐ and conspecific preen gland secretions, which are known to contain volatile compounds, to the nests and eggs of incubating female dark‐eyed juncos Junco hyemalis. The responses to these two conditions were compared to the responses of females whose nests were treated with their own preen oil as a control condition, and to females whose nests were treated with the vehicle only. We found that females significantly reduced incubation bout length, a form of parental care, in response to alien secretions, more so if they came from a heterospecific than a conspecific. Females did not reduce incubation bout length in response to their own preen oil or to a vehicle‐only control. These results suggest that odors in the nest may influence avian parental care. However, the behavioral change was only temporary and had no effect on later hatching success. In our study population, brood parasitism by brown‐headed cowbirds is common, but resulting nest abandonment is rare; juncos are frequently able to successfully breed even with cowbird nestlings in their nests. Thus, we suggest that more extreme behavioral responses to alien odor, such as nest abandonment or egg ejection, may not be adaptive and should not be expected.     

Handicapped females receive more feedings during incubation from their mates: support for the female nutrition hypothesis

The female nutrition hypothesis posits that provisioning intensity of incubating females by their mates may depend on female needs and ensure proper incubation and a corresponding high hatching and breeding success of breeding pairs. Here, we have handicapped female pied flycatchers Ficedula hypoleuca at the beginning of incubation by clipping two primaries on each wing and filmed nests during incubation and later nestling provisioning to estimate male involvement in incubation feeding at the nest and in offspring care. Incubation feeding was more frequent at late nests. Correcting for this seasonal effect, incubation feeding was significantly affected by treatment and twice as high at experimental as at control nests. There was no effect of the experiment on female incubation attendance. The handicap did not result in any effect on hatching and breeding success, nestling growth and male or female provisioning and mass at the end of the nestling period. Males adjust their incubation feeding activity at the nest to female energetic requirements during incubation.     

Mate-sharing costs in polygynous Northern Lapwings Vanellus vanellus

In this study bigamous female Northern Lapwings Vanellus vanellus received significantly less incubation relief from their males than monogamous females. On average, monogamous males spent 34.3% of their time incubating and bigamous males 29.9%. Bigamous males divided their effort between their nests, incubating on average 9.4% on primary nests and 20.5% on secondary nests. Bigamous females compensated for the lack of male relief. Primary females incubated for 71.8% of their time, secondary females for 64.2%, while monogamous females spent 52.7% of their time incubating. As a result, there was no significant difference in total nest attentiveness among nests of different status. Primary and secondary females received equivalent incubation relief from the male. Bigamous males increased their contribution to incubation significantly as the season progressed. A bigamous male's distribution of incubation relief between his females was unrelated to female body mass, or to the degree of asynchrony between primary and secondary females in arrival and laying. Incubation time was significantly, negatively, correlated with total nest attentiveness. Monogamous females spent most time, secondary females spent an intermediate time, and primary females spent the least time on maintenance behaviour (foraging, comfort behaviour, inactivity). No significant differences were found in hatching success among females of different mating status. However, the ratio of unhatched to hatched eggs (i.e. the eggs that remained in the nest at the time of hatching) differed significantly: secondary females hatched a smaller proportion of their eggs than monogamous and primary females.     

Sex-specific fledgling success and brood sex ratio in the Great Reed Warbler (Acrocephalus arundinaceus)

We examine sex ratio variation and sex-specific probability of successful fledgling in relation to hatching date across 376 broods of Great Reed Warblers (Acrocephalus arundinaceus). The sex ratio of complete broods as well as broods with partial mortality did not deviate significantly from parity (0.5 and 0.53, respectively). Variation in sex ratio between broods was not larger than expected from binomial distribution, thus females seem not to manipulate the sex ratio of their broods in the studied population. As a consequence, sex ratio did not vary in relation to hatching date, years and fishponds. Female offspring showed lower fledgling success than their brothers, but the relationship between probability of successful fledgling and hatching date differed between sexes. Fledgling success of female offspring declined with hatching date more strongly than the success of male offspring. Thus, our study shows that Great Reed Warblers do not adjust offspring sex to match observed seasonal sex-specific variation in survival.     

Impact of nest relocation on the reproductive success of Loggerhead Turtles,Caretta caretta,in the Göksu Delta,Turkey (Reptilia: Cheloniidae)

When the nests of marine turtles are at a risk of inundation, relocation of the nests are often used in the conservation measures. Here, I determined the effect of nest relocation on Loggerhead Turtle (Caretta caretta) egg hatching success during the 2013 and 2014 nesting seasons in the Göksu Delta, Mersin, Turkey. I compared natural and relocated clutches, including those relocated before and after inundation, and evaluated 102 (94.6%) and 63 (81.1%) of survived nests in 2013 and 2014 respectively. Relocated nests experienced a 30% decrease in hatching success and a more prolonged incubation period compared to nests left in situ. Egg failure in nests relocated before and after inundation was similar in early-stage embryos, whereas it was three-fold higher in mid-stage embryos and two-fold lower in late-stage embryos. Thus, there was no significant difference in overall hatching success between the two relocation types. Moreover, there was no effect of delayed relocation of nests after inundation on hatching success. Possible impacts specific to the nesting site should be considered and explored before using nest relocation as a conservation tool. The relocation approach is recommended for nests at a high risk of inundation when the loss of nests is inevitable.     

Effects of Shiny Cowbird Molothrus bonariensis parasitism on different components of House Wren Troglodytes aedon reproductive success

Avian brood parasites, including cuckoos and cowbirds, have multiple negative effects on their hosts. We analysed the effects of Shiny Cowbird Molothrus bonariensis parasitism on different components (e.g. egg losses, hatching success, chick survival and nest abandonment) of House Wren Troglodytes aedon reproductive success. We also conducted an experiment to discriminate between two mechanisms that may reduce hatching success in parasitized clutches: lower efficiency of incubation due to the increase in clutch volume and disruption of host incubation by the early hatching of Cowbirds. Egg puncturing by Shiny Cowbirds reduced host clutch size at hatching by 10–20%, and parasitized nests had a decrease in hatching success of 40–80%. Egg losses and hatching failures were positively associated with the intensity of parasitism. Brood reduction was greater in parasitized nests, but the growth rate of the chicks that fledged was similar to that in unparasitized nests. The combined effects of egg losses, hatching failures and brood reduction decreased the number of fledged chicks by 80%. In addition, egg puncturing increased the likelihood of nest abandonment by Wrens. Experimental data showed that hatching failures occurred when there was a combination of: (1) an increase in the volume of the clutch by the addition of the Cowbird egg without removal of host eggs, and (2) the addition of the Cowbird egg before the onset of incubation. This was relatively common in House Wren nests, as Cowbirds generally parasitize before the onset of incubation. Our results indicate that Shiny Cowbird parasitism imposes a major impact on House Wrens, as it affects all components of the Wren's reproductive success.     

Egg size and offspring performance in the collared flycatcher (<Emphasis Type="Italic">Ficedula albicollis</Emphasis>): a within-clutch approach

Adaptive within-clutch allocation of resources by laying females is an important focus of evolutionary studies. However, the critical assumption of these studies, namely that within-clutch egg-size deviations affect offspring performance, has been properly tested only rarely. In this study, we investigated effects of within-clutch deviations in egg size on nestling survival, weight, fledgling condition, structural size and offspring recruitment to the breeding population in the collared flycatcher (Ficedula albicollis). Besides egg-size effects, we also followed effects of hatching asynchrony, laying sequence, offspring sex and paternity. There was no influence of egg size on nestling survival, tarsus length, condition or recruitment. Initially significant effect on nestling mass disappeared as nestlings approached fledging. Thus, there seems to be limited potential for a laying female to exploit within-clutch egg-size variation adaptively in the collared flycatcher, which agrees with the majority of earlier studies on other bird species. Instead, we suggest that within-clutch egg-size variation originates from the effects of proximate constraints on laying females. If true, adaptive explanations for within-clutch patterns in egg size should be invoked with caution.     

Effects of down collection on incubation temperature, nesting behaviour and hatching success of common eiders (Somateria mollissima) in west Iceland

Incubating common eiders (Somateria mollissima) insulate their nests with down to maintain desirable heat and humidity for their eggs. Eiderdown has been collected by Icelandic farmers for centuries, and down is replaced by hay during collection. This study determined whether down collecting affected the female eiders or their hatching success. We compared the following variables between down and hay nests: incubation temperature in the nest, incubation constancy, recess frequency, recess duration, egg rotation and hatching success of the clutch. Temperature data loggers recorded nest temperatures from 3 June to 9 July 2006 in nests insulated with down (n = 12) and hay (n = 12). The mean incubation temperatures, 31.5 and 30.7°C, in down and hay nests, or the maximum and minimum temperatures, did not differ between nest types where hatching succeeded. Cooling rates in down, on average 0.34°C/min and hay nests 0.44°C/min, were similar during incubation recesses. Females left their nests 0–4 times every 24 h regardless of nest type, for a mean duration of 45 and 47.5 min in down and hay nests, respectively. The mean frequency of egg rotation, 13.9 and 15.3 times every 24 h, was similar between down and hay nests, respectively. Hatching success adjusted for clutch size was similar, 0.60 and 0.67 in down and hay nests. These findings indicate that nest down is not a critical factor for the incubating eider. Because of high effect sizes for cooling rate and hatching success, we hesitate to conclude that absolutely no effects exist. However, we conclude that delaying down collection until just before eggs hatch will minimize any possible effect of down collection on females.     

Life History Trade-Offs and Behavioral Sensitivity to Testosterone: An Experimental Test When Female Aggression and Maternal Care Co-Occur

Research on male animals suggests that the hormone testosterone plays a central role in mediating the trade-off between mating effort and parental effort. However, the direct links between testosterone, intrasexual aggression and parental care are remarkably mixed across species. Previous attempts to reconcile these patterns suggest that selection favors behavioral insensitivity to testosterone when paternal care is essential to reproductive success and when breeding seasons are especially short. Females also secrete testosterone, though the degree to which similar testosterone-mediated trade-offs occur in females is much less clear. Here, I ask whether testosterone mediates trade-offs between aggression and incubation in females, and whether patterns of female sensitivity to testosterone relate to female life history, as is often the case in males. I experimentally elevated testosterone in free-living, incubating female tree swallows (Tachycineta bicolor), a songbird with a short breeding season during which female incubation and intrasexual aggression are both essential to female reproductive success. Testosterone-treated females showed significantly elevated aggression, reduced incubation temperatures, and reduced hatching success, relative to controls. Thus, prolonged testosterone elevation during incubation was detrimental to reproductive success, but females nonetheless showed behavioral sensitivity to testosterone. These findings suggest that the relative importance of both mating effort and parental effort may be central to understanding patterns of behavioral sensitivity in both sexes.     

Conditional female strategies influence hatching success in a communally nesting iguana

The decision of females to nest communally has important consequences for reproductive success. While often associated with reduced energetic expenditure, conspecific aggregations also expose females and offspring to conspecific aggression, exploitation, and infanticide. Intrasexual competition pressures are expected to favor the evolution of conditional strategies, which could be based on simple decision rules (i.e., availability of nesting sites and synchronicity with conspecifics) or on a focal individual's condition or status (i.e., body size). Oviparous reptiles that reproduce seasonally and provide limited to no postnatal care provide ideal systems for disentangling social factors that influence different female reproductive tactics from those present in offspring‐rearing environments. In this study, we investigated whether nesting strategies in a West Indian rock iguana, Cyclura nubila caymanensis, vary conditionally with reproductive timing or body size, and evaluated consequences for nesting success. Nesting surveys were conducted on Little Cayman, Cayman Islands, British West Indies for four consecutive years. Use of high‐density nesting sites was increasingly favored up to seasonal nesting activity peaks, after which nesting was generally restricted to low‐density nesting areas. Although larger females were not more likely than smaller females to nest in high‐density areas, larger females nested earlier and gained access to priority oviposition sites. Smaller females constructed nests later in the season, apparently foregoing investment in extended nest defense. Late‐season nests were also constructed at shallower depths and exhibited shorter incubation periods. While nest depth and incubation length had significant effects on reproductive outcomes, so did local nest densities. Higher densities were associated with significant declines in hatching success, with up to 20% of egg‐filled nests experiencing later intrusion by a conspecific. Despite these risks, nests in high‐density areas were significantly more successful than elsewhere due to the benefits of greater chamber depths and longer incubation times. These results imply that communal nest sites convey honest signals of habitat quality, but that gaining and defending priority oviposition sites requires competitive ability.     

Proximate causes and fitness consequences of hatching failure in lesser kestrels Falco naumanni

Hatching failure is a pervasive phenomenon in birds, but factors affecting hatchability remain poorly understood. We studied proximate causes and fitness consequences of hatching failure in a long‐monitored population of the colonial lesser kestrel Falco naumanni. We investigated whether hatchability was related to clutch characteristics, parental traits, and social or environmental features. Hatching failure represents a cost for the parents in terms of immediate fitness, since it reduced both their number of young fledged and recruits in the breeding population, even when controlling for clutch size. Hatching failure showed a non‐linear relationship with clutch size, clutches of four eggs showing higher levels of hatching success than larger or smaller clutches. Hatchability could therefore play a role in the evolution of optimal clutch size in this species, at least constraining the maximum number of eggs the parents can afford to incubate. Contrary to most studies, the mean volume of the clutch and the individual egg volume were negatively related to hatching failure, indicating that large eggs have thermoregulatory and/or nutritional advantages. Mean daily maximum temperature during incubation affected hatching success negatively, but only for females in poor condition. This result seems to indicate that females are reluctant to jeopardize their own condition, but instead sacrifice incubation effort by paying the costs of a lower hatching success in circumstances of high temperatures. There was no evidence that hatching failure was related to the intrinsic properties of individuals or genetic similarity between the parents as indicated by low repeatabilities of: (1) males that bred with different females, (2) females that bred with different males, and (3) pairs breeding together in different years. Neither colony size nor subpopulation size affected hatchability. All these findings show how hatching failure is simultaneously influenced by several factors acting in a complex way, which could in part explain the apparently conflicting conclusions of empirical or even experimental studies carried out to date.     

Effects of testosterone implants on pair behaviour during incubation in the Yellow-legged Gull Larus cachinnans

The Yellow-legged Gull Larus cachinnans is monogamous with bi-parental incubation. In this study, the effects of high levels of plasma testosterone in male Yellow-legged Gulls during the incubation period were analysed. Free-living male gulls were implanted with testosterone (T-males), and their sexual behaviour within the pair was observed and compared with that of control pairs. Egg temperatures, length of incubation and hatching success were also analysed. T-males and their mates displayed more sexual behaviour than the controls. T-males engaged in mounting behaviour with their mates, whereas control males did not. Proportionally less time was spent incubating (in relation to time present in the colony) by T-males than control males. However, the mates of T-males did not spend more time incubating than control females to compensate for male neglect, although they did spend more time on the territory. Egg temperature in T-male nests was significantly lower than in control nests, but no significant difference in the length of incubation or hatching success between the two groups was found. In birds, the effects of high testosterone levels on male behaviour during incubation have only been analysed in a polyandrous species whose females usually do not contribute to incubation. The present results thus suggest that those males of a monogamous species with bi-parental incubation that sustain high testosterone levels after laying, thus reducing their contributions to incubation, will be confronted with a lack of compensation from their mates during incubation. Finally, this lack of female compensation seems to be mediated by behavioural interactions with the male rather than by her absence from the colony.     

Density dependent effects between three competitive bird species

Summary Density and breeding success of the great tit Parus major, blue tit Parus caeruleus and collared flycatcher Ficedula albicollis were studied in nest box colony in oak forest over a period of 19 years.Intraspecific density dependent clutch size reduction was found with blue tit and great tit. In interspecific relation the high density of blue tits reduced the clutch size of great tits.In the hatching period neither intraspecific nor interspecific density dependence were showed between the tits when the third competitive species, collared flycatcher was present. The collared flycatcher significantly reduced the hatching success of both tit species and the number of fledglings of great tit.The effects of the great tits and combined density of the great and blue tits on the hatching failure and number of fledglings of collared flycatcher were found when the density of the tits was high. There were not significant relationships to the single density of blue tits.The temporal variability of the competition of the three bird species is discussed.     

How does an increase in minimum daily temperatures during incubation influence reproduction in the great tit Parus major?

Temperature variation affects all life stages of organisms, especially early development, and considering global warming, it is urgent to understand precisely its consequences. In egg‐laying species, incubation behaviour can buffer embryo developmental temperature variation and influence offspring development. We experimentally investigated the effect of an increase in minimum daily nest temperature during incubation in the great tit Parus major, by placing a hand warming pad under the nest in the evenings. As compared to controls, the experimental treatment increased nest temperature at night by an average of 4°C, and this increase carried over to the following day. We measured the consequences of this mainly nocturnal temperature increase during incubation on 1) parental behaviour (incubation and nestling feeding), 2) parental health (quantified by body condition, immune status, physiological and oxidative stress) and 3) reproductive success (nestling body condition, growth, i.e. mass gain, hatching and fledging success, and nestling immune status, physiological and oxidative stress). This study yielded three major results. First, we found that heating the nest did not change the duration of incubation as compared to controls. Second, increasing nest temperature during incubation decreased nestling feeding behaviour but did not affect parental health in terms of body condition, immune status, physiological and oxidative stress. Third, nestling mass at hatching was greater but nestling mass gain was slower in heated nests than in control nests, resulting in similar fledging mass. The present study demonstrates that increased environmental temperatures during incubation influenced nestling development in the great tit and especially hatchling mass, which might produce long‐term life history consequences.     

Ecology and Physiology of Nesting and Early Development of the American Alligator

Ambient temperatures were significantly correlated with alligator(Alligator mississippiensis) nesting activity. Nesting occurredearliest when March-April-May ambient temperatures were highest.Rainfall had no significant relationship with time of nestingactivity although water levels did affect the degree of nesting.The bulk of the nesting took place within a 2-week period eachyear. Nesting chronology and factors affecting nesting were investigatedat Rockefeller Refuge from 1964 through 1987. Courtship activitiesgenerally began in early April and progressively intensifieduntil early June. From late May through the first week of Junecourtship and copulation were intense, the females ovulated,and the high point of spermatogenesis occurred. Factors whichseriously affected nesting success were floods, droughts, andpredation. Salinity levels affected nesting densities alongthe coast. Nesting success (% of nests which produced live hatchlings)averaged 68.3% for 266 nests followed during a 4-yr study. Hatchingsuccess (% of eggs which hatched) averaged 58.2% for 154 nestsfollowed during two nesting seasons. Habitat selection, home ranges, and daily movements were delineatedfor adult males and females. Courtship occurs in deep open waterduring springtime. Adult females selectively seek out densevegetation adjacent to isolated ponds for nesting during thesummer. Adult and sub-adult males tend to prefer open waterall year round and only occasionally venture into the more secludedand heavily vegetated areas used by the females. Home rangesizes and daily movements were much larger for adult males thanfor adult females. Laboratory studies evaluated the effectsof four different egg incubation temperatures on hatching success,sex determination, size at hatching, and growth rates to 18mo of age. The results indicate that incubation temperaturecan have a profound effect on sex ratios, hatchling size, andpost-hatching growth. No significant differences were observedin hatching success at the four different temperatures.     

Dynamics of female choice for parental care in a fish species where care is facultative

In the peacock wrasse (Symphodus tinca), females either placetheir eggs in a nest under the care of a male or disperse theireggs widely so that they receive no protection. The same femalecan spawn in both modes. Females appear to prefer males withnests early in the nesting cycle, and they spawn less oftenthan expected in late-cycle nests and with non-nesting males.Survival and hatching success are consistently higher for eggsplaced in early nests, particularly in mid-season when egg predationis intense and hatching times are relatively long. Nevertheless,30%-80% of females place their eggs outside nests, even whenhatching success is more than four times greater with care.A model incorporating search time for nests correctly predictedthe qualitative changes in the tendency of females to choosecare or no care over the course of the mating season. Extensionsof the model suggest that in the early part of the season, whennests are rare and the relative survival advantage of parentalcare is small, females should sample no more than one nest beforeopting for no care. In mid-season, when the advantages of careare highest and between-nest travel times are low, females areestimated to visit at least 8 nests before abandoning the effort,corresponding to a giving-up time of about 43 min of search.Later in the season, when short hatching times reduce the relativebenefit of care, females are estimated to visit between 4 and5 nests before giving up, corresponding to about 31 min of search.We suggest that the variability in parental care in this speciesarises from seasonal changes in relative costs and benefitsof care for the two sexes.