Incubation Bouts Research Articles

Vocal interactions of breeding partners predict duration of incubation bout in an Artic seabird

In species with biparental care, coordination of parental activities can have important fitness consequences. However, specific behavioral mechanism allowing the coordination of breeding partners remains largely unexplored. Prevalence of biparental care in seabirds makes this group particularly interesting for investigation of behavioral underpinnings of parental coordination. Here, we examined vocal behavior at the nest site of breeding partners and its role in shaping their parental share during incubation in the little auk (Alle alle). We evaluated two hypotheses related to the mechanisms involved in parental coordination: (1) behavioral adjustment, where a parent adjusts its effort according to the preceding effort of its partner and (2) vocal negotiation, where effort is adjusted based on information exchanged during the preceding vocal interaction. We found that little auk partners equally share their incubation time, although, duration of nest attendance is highly variable. No immediate reciprocity between partners in the time allocated to parental activity was observed as predicted by behavioral adjustment. However, nest attendance appeared to be related to the vocal interaction between partners during turn-taking. The duration of a given attendance was positively associated to the pair’s vocal activity and amount of vocal overlap occurring during turn-taking at the nest. Our results suggest a role of vocalization for coordinating between breeding pairs, providing a potential mechanism for the communication of information enabling this complex interaction.

Biparental incubation behaviour under temperature extremes in sandbank nesting black skimmers.

Birds nesting on riverine beaches are exposed to large temperature fluctuations, while changing water levels pose flooding risks. We used miniature temperature loggers (iButtons®) placed in nests and on the beach surface combined with time-lapse photography to study incubation behaviour in the black skimmer (Rynchops niger) on the Manu River, Peru. Since the species exhibits sexual size dimorphism, we could identify partner switches in images and the contribution to incubation effort by each pair member. Results of the study documented that nest temperature was less affected by ambient temperature and fluctuated less than the surroundings. Despite shorter incubation bouts at midday, black skimmers maintained a close to constant presence at the nest by more frequent nest exchanges. In fact, while female black skimmers generally incubated more and for longer than males, pairs shared incubation most consistently during the hottest part of the day. Incubation probability decreased around dusk, a peak foraging time for the species and a time when beach temperature overlapped with nest temperature. A biparental incubation strategy across the diel cycle appears to allow black skimmers breeding at the Manu River to incubate in challenging thermal conditions, but further studies are needed to determine proximity to thermal limits.

First Account of the Breeding Biology of Indian Blue Robin (Larvivora brunnea) in Southwest China.

Breeding biology lies at the core of life history research on birds, and it provides important information for avian conservation. We discovered one nest of the Indian Blue Robin (Larvivora brunnea) on 28 May 2021, at the Laojun mountains in Lijiang, northwestern Yunnan, China. Field observation was combined with the use of a GoPro camera for video shooting to quantitatively study the incubation and brooding behavior. We also conducted measurements of the eggs and nestlings on site and inspected the nesting materials used. A bowl-shaped nest with four eggs was located at 2830 m in the evergreen deciduous broad-leaved forest. All eggs were successfully incubated and two nestlings fledged on 22 June 2021, resulting in a total breeding success of 50%. Only the female bird incubated the eggs and brooded the nestlings. The incubation period was at least 13 days and the nestling period was 13 days. As incubation progressed, the incubation bout duration decreased. During the incubation period, the nesting time of the female bird shows a declining trend as incubation progresses. Both parents participated in feeding the nestling, and the frequency of parental supply increased with the maturity of the nestling.

Nest attendance, incubation constancy, and onset of incubation in dabbling ducks.

In birds, parents must provide their eggs with a safe thermal environment suitable for embryonic development. Species with uniparental incubation must balance time spent incubating eggs with time spent away from the nest to satisfy self-maintenance needs. Patterns of nest attendance, therefore, influence embryonic development and the time it takes for eggs to hatch. We studied nest attendance (time on the nest), incubation constancy (time nests were at incubation temperatures), and variation in nest temperature of 1,414 dabbling duck nests of three species in northern California. Daily nest attendance increased from only 1-3% on the day the first egg was laid to 51-57% on the day of clutch completion, and 80-83% after clutch completion through hatch. Variation in nest temperature also decreased gradually during egg-laying, and then dropped sharply (33-38%) between the day of and the day after clutch completion because increased nest attendance, particularly at night, resulted in more consistent nest temperatures. During the egg-laying stage, nocturnal nest attendance was low (13-25%), whereas after clutch completion, nest attendance was greater at night (≥87%) than during the day (70-77%) because most incubation recesses occurred during the day. Moreover, during egg-laying, nest attendance and incubation constancy increased more slowly among nests with larger final clutch sizes, suggesting that the number of eggs remaining to be laid is a major driver of incubation effort during egg-laying. Although overall nest attendance after clutch completion was similar among species, the average length of individual incubation bouts was greatest among gadwall (Mareca strepera; 779 minutes), followed by mallard (Anas platyrhynchos; 636 minutes) and then cinnamon teal (Spatula cyanoptera; 347 minutes). These results demonstrate that dabbling ducks moderate their incubation behavior according to nest stage, nest age, time of day, and clutch size and this moderation likely has important implications for egg development and overall nest success.

Use of geolocators for investigating breeding ecology of a rock crevice-nesting seabird: Method validation and impact assessment.

Investigating ecology of marine animals imposes a continuous challenge due to their temporal and/or spatial unavailability. Light-based geolocators (GLS) are animal-borne devices that provide relatively cheap and efficient method to track seabird movement and are commonly used to study migration. Here, we explore the potential of GLS data to establish individual behavior during the breeding period in a rock crevice-nesting seabird, the Little Auk, Alle alle. By deploying GLS on 12 breeding pairs, we developed a methodological workflow to extract birds' behavior from GLS data (nest attendance, colony attendance, and foraging activity), and validated its accuracy using behavior extracted from a well-established method based on video recordings. We also compared breeding outcome, as well as behavioral patterns of logged individuals with a control group treated similarly in all aspects except for the deployment of a logger, to assess short-term logger effects on fitness and behavior. We found a high accuracy of GLS-established behavioral patterns, especially during the incubation and early chick rearing period (when birds spend relatively long time in the nest). We observed no apparent effect of logger deployment on breeding outcome of logged pairs, but recorded some behavioral changes in logged individuals (longer incubation bouts and shorter foraging trips). Our study provides a useful framework for establishing behavioral patterns (nest attendance and foraging) of a crevice-nesting seabird from GLS data (light and conductivity), especially during incubation and early chick rearing period. Given that GLS deployment does not seem to affect the breeding outcome of logged individuals but does affect fine-scale behavior, our framework is likely to be applicable to a variety of crevice/burrow nesting seabirds, even though precautions should be taken to reduce deployment effect. Finally, because each species may have its own behavioral and ecological specificity, we recommend performing a pilot study before implementing the method in a new study system.

Double-broodedness, burial of faecal sacs and long breeding season in the Australian Logrunner in south-eastern Queensland

Observations of a female Australian Logrunner Orthonyx temminckii building a nest while feeding juveniles from a previous brood and, in the following year, incubating eggs while feeding a juvenile, represent the first documented evidence of multi-broodedness in this species. Consistent with the literature, incubation of eggs and feeding of nestlings were performed only by the female, which was fed frequently by the male when she was off the nest. Incubation attentiveness was 60%, and average incubation bouts were about twice the duration of absence bouts (44 vs 21 minutes) at one nest. Based on dates extrapolated from the date of fledging, brooding of the two nestlings ceased between Days 5 and 9. The hourly food-provisioning rate of nestlings increased linearly from 2.4 on Day 4 to 10 feeding visits on the day before fledging. Absence bouts during both the incubation and nestling period were apparently shorter, and food-provisioning rates substantially higher, than in the phylogenetically related Chowchilla O. spaldingii of Far North Queensland. Observations of the female Logrunner burying faecal sacs corroborate a previous observation in south-eastern Queensland and suggest a novel strategy to avoid attracting potential nest predators. Although the Logrunner is often thought to breed only in winter, records from multiple sources indicate that in Queensland >50% of clutches are laid during the rest of the year, presumably facilitated by year-round food availability.

Multiple individuals incubating and nest building, and winter breeding, in the Black-chinned Honeyeater Melithreptus gularis

The role of the male and female in the incubation of eggs is unknown in 30 of the 70 species of Australian honeyeaters, but in most of the remainder, only the female is thought to incubate. Nevertheless, incubation by both male and female is known to occur in six species, including the Brown-headed Honeyeater Melithreptus brevirostris. I observed and video-recorded activities at two nests of one group of four Black-chinned Honeyeaters M. gularis gularis in south-eastern Queensland. Nest attentiveness (incubation constancy) averaged 88% over three sample days. At least two birds participated in incubation, as evidenced by numerous change-overs, strongly suggesting that both male and female were involved. Incubation bouts averaged 7.2 minutes, but varied significantly over the 3 days, and off-bouts averaged 1.3 minutes but did not vary significantly. Nestling provisioning rates varied from 7.5 to 14.4 feeds h-1 on the fourth and thirteenth days after the estimated hatching day. Although cooperative breeding could not be confirmed, up to three birds were seen at this nest during the nestling stage, and up to three at the second nest before incubation began. Breeding records indicate that in south-eastern Queensland laying peaks in winter, beginning in late autumn, 2 months earlier than records suggest in New South Wales.

On the incubation behavior of Evening Grosbeaks (Coccothraustes vespertinus)

Knowledge of the breeding behavior of Evening Grosbeaks (Coccothraustes vespertinus) is based largely on a multiyear study in Colorado during the 1980s. In Colorado, the duration of full incubation bouts by female grosbeaks had a mean of 26.6 min, a value repeated since then in the literature. For one nesting pair of grosbeaks I studied in Montana, full incubation bouts (n = 5) by the undisturbed female during 22 h of direct nest watches on 7 d in June 2018 had a mean of 112.6 min (range = 45–202 min), much longer than the value reported in the Colorado study. Incomplete incubation bouts (female already incubating on my arrival or at my departure) by the undisturbed Montana female (n = 11) during the same observation period had a mean of 56.2 min, 4 of which were a minimum of 94–146 min, further suggesting that longer duration incubation bouts may be the norm for this species. Duration of incubation bouts for Evening Grosbeak in the Colorado study appear to be brief relative to other North American fringillids, but my limited data suggest that Evening Grosbeaks are typical in this regard. Mean duration of 10 nest absences by the undisturbed Montana incubating female was 9.7 ± 7.6 min (range = 3–26 min), similar to the Colorado study (10.1 ± 10.7 min). Male behavior during incubation also appeared similar to results from Colorado (no attending the eggs, frequent exchange of vocalizations with the nesting female, escorting and feeding the female only when off the nest). I conclude that the duration of nest watches (60–80 min) in the Colorado study was inadequate to determine the length of many longer incubation bouts by female Evening Grosbeaks.

Female ornamentation, incubation behavior, and reproductive success in a wild bird

In many species, both males and females possess sexual signals, but most research focuses on understanding signal expression in males. Females are often assumed to possess signals as a non-functional by-product of selection on males, but increasing evidence demonstrates functional explanations for variation in female signals. Theory suggests that—for many bird species—differences in long-term fitness associated with female signaling are more likely to be driven by variation in offspring quality than quantity, but research paradigms developed for studying male signals have primarily focused on counting offspring produced. Here, we tested the hypothesis that female ornamentation reliably signals the ability to incubate effectively. We used temperature loggers placed in the nest of common yellowthroat warblers (Geothlypis trichas) to record incubation behavior across multiple breeding attempts. Incubation bout length and the onset of daily activity were highly variable between females, but repeatable within females across multiple nesting attempts. Females with longer bouts and later onset of activity had higher hatching success. Wing length and plumage coloration were not related to incubation length or onset of activity, but were correlated with the total percentage of time spent on the nest each day. However, there was only a trend for repeatability in percentage of time spent on the nest and this measure was not correlated with any metrics of offspring quality or hatching success that we recorded. Therefore, we did not find any single aspect of incubation behavior that was (i) consistent, (ii) related to nestling quality or success, and (iii) signaled by ornamentation. Our results demonstrate the importance of variation in incubation behavior, but also suggest that ornaments are of limited utility as a signal of incubation ability in this species. Nevertheless, our study highlights the need to explore alternative fitness proxies in order to understand variation in female ornamentation. Choosing a high-quality mate is an important determinant of reproductive success and animals often attend to elaborate ornaments as signals of quality during mate choice. In many species, both males and females have ornaments, but most research has focused on male signals and female mate choice. We found that female incubation behavior is associated with both plumage ornaments and hatching success, but there was no single signal that provided reliable information about the aspects of incubation behavior that were related to reproductive success. Our findings suggest that understanding female ornamentation may depend on considering the specific ways that females contribute to offspring survival.

Does the intrusion of an avian nest predator elicit a change in the behaviour of a canopy-nesting passerine?

Abstract Many studies have shown that nest predators affect their prey indirectly by inducing changes in the behaviour of the prey. Studies suggest that the type and degree of nest defence strategies depends heavily on species, along with nest type and location. One such strategy, nest vigilance, allows individuals to collect information and make informed decisions based on their surroundings. In this study, we simulated the intrusion of a common avian nest predator (blue jay, Cyanocitta cristata) into the territory of nesting cerulean warblers (Setophaga cerulea) and evaluated eight different behavioural variables to determine their response to the nest predator. Female cerulean warblers were more vigilant on their nest when exposed to a potential predator compared to a nest with lower threat of predation. Females exposed to a nest predator increased incubation bout by 109% and brooding bout by 60%. Our data also suggest that male cerulean warblers reduce their provisioning rate during the early nestling stage (−1 feeding/hour) and late nestling stage (−3 feedings/hour), although more data are needed. Modification of incubation bout length and nestling provisioning rate are common strategies employed by songbirds to reduce activity around the nest, by decreasing detection opportunities of visually-oriented nest predators. Currently, the only understanding we have on how cerulean warblers respond to a nest predator is based on observational data. The results of this study provide the first evidence that cerulean warblers are able to identify species that pose a threat to the safety of their nest, and that they modify their behaviour to reduce nest detection by predators. The results of this study provide a better understanding of a relatively unknown aspect of the breeding behaviour of this species. This study is also first to describe how an open-cup, canopy-nesting species responds to an increase in nest predation threat.

Incubation Behavior Differences in Urban and Rural House Wrens, Troglodytes aedon

As global land surfaces are being converted to urban areas at an alarming rate, understanding how individuals respond to urbanization is a key focus for behavioral ecology. As a critical component of avian parental care, incubating adults face a tradeoff between maintaining an optimal thermal environment for the developing embryos while meeting their own energetic demands. Urban habitats are biotically and abiotically different from their rural counterparts,i.e., in food availability, predator compositions, and the thermal environment. Therefore, urban birds may face different incubation challenges than their natural counterparts. We measured incubation behavior of rural and urban house wrens,Troglodytes aedon, with temperature loggers throughout the 12-day period. We found that urban females had more incubation bouts of shorter duration and spent less total time incubating per day than rural females. Results could provide evidence of behavioral shifts of wrens in cities, which have implications for the evolution of parental care. Our findings contribute to our understanding of the behavioral traits needed for city life and possible environmental pressures driving urban adaptations.

Higher experimental ambient temperature decreases female incubation attentiveness in Zebra Finches (Taeniopygia guttata) and lower effort yields negligible energy savings

In birds, ambient temperature can influence adult incubation behaviour, energy budget, egg temperature and embryonic development, with downstream effects on offspring survival. Surprisingly, experimental manipulations of the whole nesting environment to test causes and consequences of variation in incubation pattern, energy balance, egg temperature and the duration of development are lacking to date. Here, we bred pairs of Zebra Finches Taeniopygia guttata under controlled conditions at 18 and 30 °C and measured clutch size, temperature, hatching success, parental attentiveness and the length of the embryonic period. We found that when breeding at the higher temperature, males, but not females, increased the number of incubation bouts on the nest. Instead, females, but not males, reduced their attentiveness towards the clutch overall. Eggs showed no temperature differences between the two treatments and bigger clutches experienced lower temperatures. This suggests that parental behaviour may buffer the effect of ambient conditions on the thermal profile of eggs, including species with high rates of parental attentiveness. Warmer conditions yielded higher hatching rates but did not cause measurable differences in the length of embryonic development. Still, smaller clutches hatched earlier in accordance with the higher temperature experienced. Additionally, we used data from the literature to calculate parental energy expenditure and demonstrate that this was substantially different across the two treatments, although predicted energy savings from reduced attentiveness at 30 °C appeared negligible. These results suggest that when food is available, ambient temperature and not energy trade‐offs may explain variation in incubation behaviour.

Temperature-mediated plasticity in incubation schedules is unlikely to evolve to buffer embryos from climatic challenges in a seasonal songbird.

Phenotypic plasticity is hypothesized to facilitate adaptive responses to challenging conditions, such as those resulting from climate change. However, tests of the key predictions of this 'rescue hypothesis', that variation in plasticity exists and can evolve to buffer unfavourable conditions, remain rare. Here, we investigate among-female variation in temperature-mediated plasticity of incubation schedules and consequences for egg temperatures using the chestnut-crowned babbler (Pomatostomus ruficeps) from temperate regions of inland south-eastern Australia. Given recent phenological advances in this seasonal breeder and thermal requirements of developing embryos (>~25°C, optimally ~38°C), support for evolutionary rescue-perhaps paradoxically-requires that plasticity serves to buffer embryos more from sub-optimally low temperatures. We found significant variation in the duration of incubation bouts (mean±SD=27±22min) and foraging bouts (mean±SD=17±11min) in this maternal-only incubator. However, variation in each arose because of variation in the extent to which mothers increased on- and off-bout durations when temperatures (0-36°C) were more favourable rather than unfavourable as required under rescue. In addition, there was a strong positive intercept-slope correlation in on-bout durations, indicating that those with stronger plastic responses incubated more at average temperatures (~19°C). Combined, these effects reduced the functional significance of plastic responses: an individual's plasticity was neither associated with daily contributions to incubation (i.e. attentiveness) nor average egg temperatures. Our results highlight that despite significant among-individual variation in environmental-sensitivity, plasticity in parental care traits need not evolve to facilitate buffering against unfavourable conditions.

Sex‐specific effects of predation risk on parental care in a sexually dichromatic Neotropical songbird

Predation risk affects a broad range of bird behaviours, especially parental care. The adaptive behavioural changes presented by both parents, however, may differ according to different levels of predation risk suffered by each sex. This is especially prominent in sexually dichromatic species, where one of the sexes is more visually conspicuous and hence vulnerable to increased nest predation risk during nest visits. Here, we experimentally investigated how predation risk affects the parental behaviour of a sexually dichromatic Neotropical passerine, the blue‐black grassquit Volatinia jacarina. We used playbacks of known predators and non‐predatorial control sympatric species near nesting pairs in the field. Results show that grassquits modify their behaviour according to predation risk and that this behavioural response is sex‐dependent. Males decrease their nest visit times, become more discreet when moving towards the nest, and stop performing sexual displays after leaving the nest. In contrast, females tend to decrease latency to visit the nest and increase the duration of brooding bouts. These different sex responses reduce nest visual and acoustic detectability, since conspicuous males are readily spotted on nests and cryptic females camouflage nestlings and suppress begging calls. Although these behavioural changes might reduce predation risk, there might be a cost of reduced food load to nestlings and increased brood starvation risk. These changes in nesting activities illustrate the behavioural adaptability of passerines to ensure offspring survival in tropical high predation risk environments.

Parental investment does not directly affect reproductive success in the saffron finch

In tropical species, the study of parental care and the description of the intraspecific variation of parental care remain relatively understudied, especially when compared to the vast works dedicated to species from the Northern Hemisphere. In Colombia, the saffron finch Sicalis flaveola, is a species with a wide geographical distribution, and despite its abundance in open habitats and urban environments, little is known about its reproductive ecology. As a small‐bodied, short‐lived passerine, we postulated that the saffron finch should behave according to the ‘reproductive value hypothesis', investing in the current brood at the expense of future survival. Consequently, we predicted: 1) that parental investment would be associated with brood size and 2) parental investment would be positively associated with nestling growth rate and reproductive success (defined as the number of nestlings which reached fledging age). In 2018, two reproductive peaks of S. flaveola flaveola were documented in the Meléndez campus of Universidad del Valle, Cali. Direct observations and video cameras (> 1700 h of recording) were used to monitor the nests from 38 different breeding pairs. We found that feeding visits and the number of regurgitation events were positively related to brood size. In an experiment of simulated nest predation, 85% of breeding pairs responded to the stimulus and parents who exhibited highly responsive behaviours (50%) raised nestlings with a higher growth rate. We also found that egg surface area positively affected the number of incubation bouts per hour. Whilst no relationship was found between overall parental investment and reproductive success, our results appear to show that the intensity of parental investment during reproduction was modulated by brood size. Our findings suggest that there are multiple ecological factors that influence reproductive success in the saffron finch, and reinforce the need for longer term studies of tropical passerines.

Coordination in parental effort decreases with age in a long‐lived seabird

Biparental care is widespread in avian species. Individuals may match the contribution of their partner, resulting in equal parental effort, or may exploit their partner, to minimise their own investment. These two hypotheses have received much theoretical and empirical attention in short‐lived species, that change mates between seasons. However, in species with persistent pair bonds, where divorce is rare and costly, selective pressures are different, as partners share the value of future reproduction. In such species, coordination has been suggested to be adaptive and to increase early in life, as a consequence of the importance of mate familiarity. However, as birds age, an increase in re‐pairing probability occurs in parallel to a decline in their survival probability. At the point when partners no longer share future reproductive success, exploitation of a partner could become adaptive, reducing selection for coordinated effort. As such, we suggest that coordination in parental effort will decline with age in long‐lived species. Using incubation bout duration data, estimated from salt‐water immersion bio‐loggers, deployed on black‐browed albatrossesThalassarche melanophris, we examined the correlation in incubation bout durations for sequential bouts, as a measure of coordination. Our results show that coordination is highest in inexperienced pairs (early in reproductive life) and declines throughout the lifetime of birds. This suggests that both cooperation, indicated by coordinated effort, and conflict over care occurs in this species. We find no change in individual bout duration with increasing breeding experience, and hence no support for the hypothesis that aging leads to changes in individual incubation behaviour. This is, to our knowledge, the first study to demonstrate strong coordination in parental care when pairs share future reproductive success, but a decline in coordination with age, as sexual conflict increases.

Nesting biology of Green-and-gold tanager (Tangara schrankii): unique traits for lowland reproductive success?

ABSTRACT The Green-and-Gold Tanager (Tangara schrankii) is widely distributed throughout western Amazonia, between 300 and 1650 m, and is a common member of canopy and midstory mixed-species flocks. Although basic nesting aspects are known for this species, detailed information is lacking. This study provides new insights on nesting behaviour and natural history for this species based on 150 nests encountered during eight consecutive nesting seasons in southeastern Peru, Manu National Park. Nests were located between 0.3 and 4.5 m above the ground. The incubation and nestling periods lasted 16 and 13.4 days, respectively. Females conducted 6.2 ± 1.96 off-bouts per day and spent long incubating sessions of 77.4 ± 51.9 min. The length of the incubation bouts and the frequency (trips per day) did not vary across the three stages (early, middle, and late) of the incubation period. The overall daytime nest attentiveness was 65.4% and did not vary along the incubation period. Parents conducted 1.77 ± 1.02 feeding trips per hour. The daily survival rate (0.75) of this species was low compared to other passerines. Our data is consistent with previous T. schrankii nesting descriptions. Nestling period, and feeding rates, however, are much shorter compared to previous reports for other Tangara and related genera. We found that T. schrankii has different nesting strategies, such as locating nests on a variety of substrates, conducting long incubation sessions, fewer off-bouts, and lower feeding rates. These strategies could reduce nest detectability by visual predators, and shorten the nestling period, likely increasing their reproductive success. We suggest that the combination of these nesting traits has allowed T. schrankii to successfully inhabit lowland tropical forests where high predation levels are encountered by nesting birds.

Variation in Biparental Incubation Patterns of the Black-Faced Spoonbill (Platalea minor)

This study was conducted using wildlife cameras at nests in a colony of Black-faced Spoonbill (Platalea minor) on Mae-do Islet (37° 34′ 07.17″ N, 126° 35′ 08.10″ E), Incheon, South Korea to monitor and examine the variation in incubation patterns between males and females among four different stages of incubation (Egg-laying, Early-, Mid-, and Late-incubation stage). Mean egg-incubation bout length was longer for females (Egg-laying stage = 6.55 ± 0.44 hr SE; Early-incubation = 7.34 ± 0.48 hr; Mid-incubation = 7.22 ± 0.44 hr; Late-incubation = 7.89 ± 0.58 hr) than for males (Egg-Laying = 4.55 ± 0.39 hr; Early-incubation = 6.35 ± 0.46 hr; Mid-incubation = 6.94 ± 0.40 hr; Late-incubation = 7.07 ± 0.51 hr), but the differences in average incubation bout length between females and males decreased after the Egg-laying stage. Females incubated a greater proportion of time during nighttime (Females: 88.21 ± 3.73%; Males: 11.79 ± 3.73%), and males incubated a greater proportion of time during daytime (Female: 25.19 ± 3.48%, Male: 74.80 ± 3.48%) after the egg-laying stage. This study suggests that Black-faced Spoonbills divide their duties according to diel schedule and adjust the incubation duration throughout the entire incubation period.

Extra-pair mating opportunities mediate parenting and mating effort trade-offs in a songbird

Abstract In socially monogamous species with bi-parental care, males may face a trade-off between providing parental care and pursuing extra-pair matings. The “parenting-mating trade-off” hypothesis predicts that high-quality males—who have greater potential to gain extra-pair matings, for example, larger males usually win the competition for extra-pair mating—should reduce parental care and spend more time looking for extra-pair matings. However, the trade-off between parenting and mating efforts may be complicated by variation in the availability of extra-pair mating opportunities. By using field data of hair-crested drongos (Dicrurus hottentottus), a species exhibiting bi-parental incubation behavior, collected in central China from 2010 to 2017, we tested whether the potential negative relationship between male quality and paternal care was dependent on the number of nearby fertile females. We found that male drongos mainly seek extra-pair matings during the incubation period and high-quality individuals (males with longer tarsi) are more likely to sire extra-pair offspring. In agreement with the “parenting-mating trade-off” hypothesis, high-quality males incubated less by recessing longer between incubation bouts. However, this was only the case when sufficient fertile females nearby for extra-pair mating opportunities. Females compensated for reduced male care, but this was independent of male quality. This suggests that the reduction in care by high-quality males might be a direct response to extra-pair mating opportunities rather than facilitated by differential allocation of females. Our results indicate that individual quality and available mating opportunities may shape the optimal trade-off between parental care and seeking additional matings for males.

When are egg-rejection cues perceived? A test using thermochromic eggs in an avian brood parasite host.

At the core of recognition systems research are questions regarding how and when fitness-relevant decisions made. Studying egg-rejection behavior by hosts to reduce the costs of avian brood parasitism has become a productive model to assess cognitive algorithms underlying fitness-relevant decisions. Most of these studies focus on how cues and contexts affect hosts' behavioral responses to foreign eggs; however, the timing of when the cues are perceived for egg-rejection decisions is less understood. Here, we focused the responses of American robins Turdus migratorius to model eggs painted with a thermochromic paint. This technique modified an egg's color with predictably varying temperatures across incubation: at the onset of incubation, the thermochromic model egg was cold and perceptually similar to a static blue model egg (mimicking the robin's own blue-green egg color), but by the end of an incubation bout, it was warm and similar to a static beige egg (mimicking the ground color of the egg of the robin's brood parasite, the brown-headed cowbird Molothrus ater). Thermochromic eggs were rejected at statistically intermediate rates between those of the static blue (mostly accepted) and static beige (mostly rejected) model eggs. This implies that at the population level, egg-rejection relevant cues are not perceived solely when arriving to or solely when departing from the nest. We also found that robins rejected their own eggs more often when exposed to color-changing model eggs relative to static eggs, suggesting that recognizing variable foreign eggs entails costly rejection errors for this host species.