Buildings promote higher incubation temperatures and reduce nest attentiveness in a Neotropical thrush

Incubation is an energetically costly parental task of breeding birds. Incubating parents respond to environmental variation and nest‐site features to adjust the balance between the time spent incubating (i.e. nest attentiveness) and foraging to supply their own needs. Non‐natural nesting substrates such as human buildings impose new environmental contexts that may affect time allocation of incubating birds but this topic remains little studied. Here, we tested whether nesting substrate type (buildings vs. trees) affects the temperature inside the incubation chamber (hereafter ‘nest temperature’) in the Pale‐breasted Thrush Turdus leucomelas, either during ‘day’ (with incubation recesses) or ‘night’ periods (representing uninterrupted female presence at the nest). We also tested whether nesting substrate type affects the incubation time budget using air temperature and the day of the incubation cycle as covariates. Nest temperature, when controlled for microhabitat temperature, was higher at night and in nests in buildings but did not differ between daytime and night for nests in buildings, indicating that buildings partially compensate for incubation recesses by females with regard to nest temperature stability. Females from nests placed in buildings exhibited lower nest attentiveness (the overall percentage of time spent incubating) and had longer bouts off the nest. Higher air temperatures were significantly correlated with shorter bouts on the nest and longer bouts off the nest, but without affecting nest attentiveness. We suggest that the longer bouts off the nest taken by females of nests in buildings is a consequence of higher nest temperatures promoted by man‐made structures around these nests. Use of buildings as nesting substrate may therefore increase parental fitness due to a relaxed incubation budget, and potentially drive the evolution of incubation behaviour in certain urban bird populations.     

Evolution of passerine incubation behavior: influence of food, temperature, and nest predation

Abstract.— Incubation behavior is one component of reproductive effort and thus influences the evolution of life-history strategies. We examined the relative importance of body mass, frequency of mate feeding, food, nest predation, and ambient temperature to explain interspecific variation in incubation behavior (nest attentiveness, on- and off-bout durations, and nest trips per hour) using comparative analyses for North American passerines in which only females incubate. Body mass and frequency of mate feeding explained little variation in incubation behavior. We were also unable to detect any influence of food; diet and foraging strategy explained little interspecific variation in incubation behavior. However, the typical temperature encountered during reproduction explained significant variation in incubation behavior: Species breeding in colder environments take shorter bouts off the nest, which prevents eggs from cooling to temperatures below the physiological zero temperature. These species must compensate for shorter off-bouts by taking more of them (thus shorter on-bouts) to obtain needed energy for incubation. Nest predation also explains significant variation in incubation behavior among passerines: Species that endure high nest predation have evolved an incubation strategy (long on- and off-bouts) that minimizes activity that could attract predators. Nest substrate explained additional variation in incubation behavior (cavity-nesting birds have shorter on-bouts and make more frequent nest trips), presumably because nest predation and/or temperature varies among nest substrates. Thus, nest predation can influence reproductive effort in a way previously not demonstrated–by placing a constraint on parental activity at the nest. Incubating birds face an ecological cost associated with reproductive effort (predation of entire brood) that should be considered in future attempts to explain avian life-history evolution.     

Nest attendance by tropical and temperate passerine birds: Same constancy,different strategy

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Delayed egg‐laying and shortened incubation duration of Arctic‐breeding shorebirds coincide with climate cooling

Biological impacts of climate change are exemplified by shifts in phenology. As the timing of breeding advances, the within‐season relationships between timing of breeding and reproductive traits may change and cause long‐term changes in the population mean value of reproductive traits. We investigated long‐term changes in the timing of breeding and within‐season patterns of clutch size, egg volume, incubation duration, and daily nest survival of three shorebird species between two decades. Based on previously known within‐season patterns and assuming a warming trend, we hypothesized that the timing of clutch initiation would advance between decades and would be coupled with increases in mean clutch size, egg volume, and daily nest survival rate. We monitored 1,378 nests of western sandpipers, semipalmated sandpipers, and red‐necked phalaropes at a subarctic site during 1993–1996 and 2010–2014. Sandpipers have biparental incubation, whereas phalaropes have uniparental incubation. We found an unexpected long‐term cooling trend during the early part of the breeding season. Three species delayed clutch initiation by 5 days in the 2010s relative to the 1990s. Clutch size and daily nest survival showed strong within‐season declines in sandpipers, but not in phalaropes. Egg volume showed strong within‐season declines in one species of sandpiper, but increased in phalaropes. Despite the within‐season patterns in traits and shifts in phenology, clutch size, egg volume, and daily nest survival were similar between decades. In contrast, incubation duration did not show within‐season variation, but decreased by 2 days in sandpipers and increased by 2 days in phalaropes. Shorebirds demonstrated variable breeding phenology and incubation duration in relation to climate cooling, but little change in nonphenological components of traits. Our results indicate that the breeding phenology of shorebirds is closely associated with the temperature conditions on breeding ground, the effects of which can vary among reproductive traits and among sympatric species.     

Supplemental food alters nest defence and incubation behaviour of an open‐nesting wetland songbird

Climate‐driven increases in spring temperatures are expected to result in higher prey availability earlier in the breeding season for insectivorous birds breeding in wetland habitats. Predation during the incubation phase is a major cause of nesting failure in open‐nesting altricial birds such as the Eurasian reed warbler. The nest predation rate in this species has recently been shown to be substantially reduced under conditions of experimentally elevated invertebrate prey availability. Food availability near the nest may be an important determinant of adult incubation and nest defence behaviours during the incubation period. We used two experimental studies to compare incubation behaviour and nest defence in food‐supplemented and unsupplemented adult Eurasian reed warblers during the incubation phase. In the first study we measured nest defence behavioural responses to a taxidermic mount of a native predator (stoat Mustela erminea). In the second study we used temperature loggers installed in nests to measure breaks in incubation as a measure of nest vulnerability. Food‐supplemented birds responded aggressively to the presence of a predator more quickly than those in the unsupplemented group, suggesting they are closer to their nest and can more quickly detect a predator in the vicinity. Food‐supplemented birds also had shorter breaks in incubation (both in terms of maximum and mean off‐bout durations), presumably because they were foraging for shorter periods or over shorter distances from the nest. This study therefore identifies the behavioural mechanisms by which changes in food availability may lead to changes in nest survival and thus breeding productivity, in open‐nesting insectivorous birds.     

Incubation feeding by male Scarlet Tanagers: a mate removal experiment

ABSTRACT Incubation feeding, where males feed their mates, is a common behavior in birds and may improve female condition, nest attentiveness, and nesting success. We used behavioral observations and a temporary mate removal experiment to test the female nutrition hypothesis for incubation feeding by male Scarlet Tanagers (Piranga olivacea). All males (N= 20) were observed incubation feeding and fed females both at the nest (x? 1.36 trips/h) and away from the nest (x? 20.1 trips/h). Male feeding rate off‐nest was negatively correlated with the duration of female foraging bouts and positively correlated with the total time females spent incubating per hour. Eggs were predated at seven of 19 (37%) nests, but nest survival during incubation was not related to either female incubation behavior or male feeding rate. During temporary removal experiments (N= 12), female Scarlet Tanagers remained on the nest significantly longer and did not have longer foraging bouts. An unexpected outcome of the removal experiments was a dramatic change in female vocal behavior. All 12 experimental females gave chik‐burr calls during the male‐removal experiments (x? bout length = 11.7 min), but during normal observation periods only six of 20 females at the incubation stage gave chik‐burr calls (x? bout length = 0.7 min, N= 20). Our results suggest that female tanagers likely gain nutritional benefits from incubation feeding, but male feeding may not improve immediate reproductive success. Nine of 54 (17%) nestlings in five of 17 broods (29%) were extra‐pair young (EPY), indicating that males could potentially benefit from incubation feeding via mate retention and fidelity as well as, or instead of, through immediate gains in reproductive success. Our study indicates that females benefit from incubation feeding and do not simply passively accept food from their mates, but instead may influence male feeding rates through direct (e.g., mate following and vocalizing) and indirect (the threat of mate abandonment or cuckoldry) means.     

Low incubation investment in the burrow‐nesting Crab Plover Dromas ardeola permits extended foraging on a tidal food resource

We used GPS data‐loggers, video‐recordings and dummy eggs to assess whether foraging needs may force the low incubation attentiveness (< 55%) of the Crab Plover Dromas ardeola, a crab‐eating wader of the Indian Ocean that nests colonially in burrows. The tidal cycle was the major determinant of the time budget and some foraging trips were more distant from the colony than previously known (up to 26 km away and lasting up to 45 h). The longest trips were mostly made by off‐duty parents, but on‐duty parents also frequently left the nest unattended while foraging for 1–7 h. However, the time spent at the colony area (47%) and the time spent roosting on the foraging grounds (16%) would have allowed almost continuous incubation, as in other species with shared incubation. Therefore, the low incubation attentiveness is not explained by the need for long foraging trips but is largely dependent on a high intermittent rhythm of incubation with many short recesses (5.8 ± 2.6 recesses/h) that were not spent foraging but just outside the burrow or thermoregulating at the seashore. As a result, the eggs were warmed on average only 1.7 °C above burrow temperature, slightly more during high tide periods and when burrow temperature was lower between 20:00 and 10:00 h, only partly counteracting the temperature fluctuations of the incubation chamber. These results suggest that low incubation attentiveness is due to the favourable thermal conditions provided by safe nesting burrows and by the hot tropical breeding season, a combination that allows simultaneous foraging by parents and the exploitation of distant foraging grounds. Why Crab Plovers engage in many short recesses from incubation still remains to be clarified but the need to thermoregulate at the seashore and to watch for predators may play a role.     

Local variation in weather conditions influences incubation behavior and temperature in a passerine bird

Incubation is an important component of avian parental care and slight changes in incubation temperature can affect offspring phenotype. Although many extrinsic and intrinsic factors may generate variation in incubation temperature, they remain underexplored under natural conditions. Using a robust data set encompassing 55 nests, 22 816 behavioral observations, and > 1 million paired ambient and egg temperatures, we describe the relationships among abiotic factors, female incubation behavior, incubation temperature, and incubation period for tree swallows Tachycineta bicolor. We report a large amount of individual variation in incubation behaviors and average incubation temperatures for our study population. The average on‐bout incubation temperature was 34.1°C, with daily egg temperatures ranging from 18.0–39.2°C. Females modulated the number of times they left the nest and the amount of time they stayed off the nest according to interactions between precipitation and temperature patterns. Models generated from our observations predicted that the number of female off‐bouts was the lowest under warm and dry conditions while more off‐bouts were taken under cold and dry or warm and wet conditions. During cold and dry conditions, females stayed off their nest ～4 times longer than under warm and dry conditions. However, this pattern was reversed under periods of rainfall; females tended to take shorter off‐bouts when it was rainy and cold compared to longer off‐bouts during warmer rain events. Furthermore, variation in female behavior was associated with differences in overall incubation temperature such that females that maintained greater incubation constancy produced higher incubation temperatures at a given ambient temperature than those that displayed lower incubation constancy. Our results provide perspective on the timing of breeding, as some of the advantages of breeding early may be countered by cooler, early season temperatures and precipitation that cause reproducing females to favor self‐maintenance at a potential cost to optimal incubation temperatures for offspring development.     

The Effect of Male Incubation Feeding,Food and Temperature on the Incubation Behaviour of New Zealand Robins

Because of finite resources, organisms face conflict between their own self‐care and reproduction. This conflict is especially apparent in avian species with female‐only incubation, where females face a trade‐off between time allocated to their own self‐maintenance and the thermal requirements of developing embryos. We recorded incubation behaviour of the New Zealand robin (Petroica longipes), a species with female‐only incubation, male incubation feeding and high nest predation rates. We examined how male incubation feeding, ambient temperature and food availability (invertebrate biomass) affected the different components of females’ incubation behaviour and whether incubation behaviour explained variation in nest survival. Our results suggest that male incubation feeding rates of 2.8 per hour affect the female’s incubation rhythm by reducing both on‐ and off‐bout duration, resulting in no effect on female nest attentiveness, thus no support for the female‐nutritional hypothesis. The incubation behaviours that we measured did not explain nest survival, despite high nest predation rates. Increased ambient temperature caused an increase in off‐bout duration, whereas increased food availability increased on‐bout duration. While males play a vital role in influencing incubation behaviour, female robins attempt to resolve the trade‐off between their own foraging needs and the thermal requirements of their developing embryos via alternating their incubation rhythm in relation to both food and temperature.     

Incubation failure and nest abandonment by Leach's Storm‐Petrels detected using PIT tags and temperature loggers

ABSTRACT The nocturnal activity of burrow‐nesting seabirds, such as storm‐petrels and shearwaters, makes it difficult to study their incubation behavior. In particular, little is known about possible differences in the incubation behavior of adults at successful and unsuccessful nests. We combined the use of passive integrated transponder (PIT) technology and nest‐temperature data loggers to monitor the incubation behavior of 10 pairs of Leach's Storm‐Petrels (Oceanodroma leucorhoa). The mean incubation bout length was 3.31 ± 0.59 (SD) days for individual adults at successful nests (N= 4) and 1.84 ± 1.16 d for individuals at unsuccessful nests (N= 6). Mean bout length for pairs in successful burrows (3.51 ± 0.56 d) did not differ significantly (P= 0.07) from that for pairs in unsuccessful burrows (1.80 ± 1.20 d), perhaps due to one failed nest with a high mean bout length (4.15 d). The total number of incubation bouts per parent (4.3 ± 1.9 bouts) did not differ with hatching success. Adults whose nests failed repeatedly exhibited truncated incubation bouts (< 12 h) prior to complete nest failure and were more likely than successful parents to make brief visits to nearby, occupied nesting burrows. Our results suggest that the decision by Leach's Storm‐Petrels to abandon a nest is not an abrupt one. Rather, failed nesting attempts may be characterized by truncated incubation bouts where individuals pay the energetic cost of travel to and from the burrow, but do not remain long enough to successfully incubate the egg.     

Incubation pattern and foraging effort in the female Water Pipit Anthus spinoletta

Incubation and foraging patterns of female Water Pipits Anthus spinoletta were studied in two breeding seasons in an Alpine valley of Switzerland. Decreased temperature reduced the length of periods spent off the nest (inattentive period), while decreased food availability led to a reduction in time spent incubating (attentiveness), shorter periods spent on the nest (attentive period), more frequent inattentive periods and higher foraging effort, measured as the product of frequency of inattentive periods and twice the flight distance to foraging sites. The negative relation between food availability and foraging effort resulted from more frequent foraging bouts and longer flight distances under poor food conditions. Feeding of the incubating female by the male did not affect foraging effort and attentiveness but did change the temporal pattern of inattentive periods from a few long to several short inattentive periods.     

Time‐lapse cameras reveal latitude and season influence breeding phenology durations in penguins

Variation in the phenology of avian taxa has long been studied to understand how a species reacts to environmental changes over both space and time. Penguins (Sphenicidae) serve as an important example of how biotic and abiotic factors influence certain stages of seabird phenology because of their large ranges and the extreme, dynamic conditions present in their Southern Ocean habitats. Here, we examined the phenology of gentoo (Pygoscelis papua) and chinstrap penguins (Pygoscelis antarctica) at 17 sites across the Scotia arc, including the first documented monitoring of phenology on the South Sandwich Islands, to determine which breeding phases are intrinsic, or rather vary across a species range and between years. We used a novel method to measure seabird breeding phenology and egg and chick survival: time‐lapse cameras. Contrary to the long‐standing theory that these phases are consistent between colonies, we found that latitude and season had a predominant influence on the length of the nest establishment, incubation, and guard durations. We observe a trend toward longer incubation times occurring farther south, where ambient temperatures are colder, which may indicate that exposure to cold slows embryo growth. Across species, in colonies located farther south, parents abandoned nests later when eggs were lost or chicks died and the latest record of eggs or chicks in the nest occurred earlier during the breeding period. The variation in both space and time observed in penguin phenology provides evidence that the duration of phases within the annual cycle of birds is not fundamental, or genetic, as previously understood. Additionally, the recorded phenology dates should inform field researchers on the best timing to count colonies at the peak of breeding, which is poorly understood.     

Incubation recess behaviors influence nest survival of Wild Turkeys

In ground nesting upland birds, reproductive activities contribute to elevated predation risk, so females presumably use multiple strategies to ensure nest success. Identification of drivers reducing predation risk has primarily focused on evaluating vegetative conditions at nest sites, but behavioral decisions manifested through movements during incubation may be additional drivers of nest survival. However, our understanding of how movements during incubation impact nest survival is limited for most ground nesting birds. Using GPS data collected from female Eastern Wild Turkeys (n = 206), we evaluated nest survival as it relates to movement behaviors during incubation, including recess frequency, distance traveled during recesses, and habitat selection during recess movements. We identified 9,361 movements off nests and 6,529 recess events based on approximately 62,065 hr of incubation data, and estimated mean nest attentiveness of 84.0%. The numbers of recesses taken daily were variable across females (range: 1?7). Nest survival modeling indicated that increased cumulative distance moved during recesses each day was the primary driver of positive daily nest survival. Our results suggest behavioral decisions are influencing trade‐offs between nest survival and adult female survival during incubation to reduce predation risk, specifically through adjustments to distances traveled during recesses.     

Effects of ambient temperature on avian incubation behavior

Ambient temperature is commonly thought to influence avian incubation behavior. However, results of empirical studies examining correlationsbetween ambient temperature and bout duration are equivocal.We propose that these equivocal results can be partly explainedby developing a conceptual understanding of how we should expecttemperature to influence incubation. We demonstrate why linearcorrelation analyses across a wide range of temperatures canbe inappropriate based on development of an incubation model for small birds that incorporates how ambient temperature influencesboth embryonic development and adult metabolism. We found supportfor predictions of the model using incubation data from orange-crownedwarblers (Vermivora celata) in Arizona. Both off- and on-boutduration were positively correlated with ambient temperaturebetween 9° and 26°C, but unrelated to ambient temperature<9° and 26-40°C. Bout durations declined as ambienttemperature approached or exceeded 40°C. Incubating orange-crowned warblers appeared to avoid bouts off the nest <7 min andbouts on the nest <20 min. Time of day, duration of theprevious bout, and variation among nests all explained variationin both on- and off-bout duration. Although we found supportfor the general shape of the incubation model, temperature still explained only a small portion of the overall variation in on-and off-bout duration. Results of previous studies were generallyconsistent with the model for off-bout duration; most studiesin colder environments reported positive correlations withtemperature, and the one negative correlation reported was from a hot environment. However, the relationships between on-boutduration and temperature reported in previous studies wereless consistent with our model and our data. Although somediscrepancies could be explained by considering our model,some studies reported negative correlations in cold environments.The effect of ambient temperature on duration of on-bouts probablydiffers among species based on the amount of fat reserves females typically carry during incubation and the extent of male incubationfeeding. Additional studies of the effects of temperature onavian incubation will help improve the general model and ultimatelyaid our understanding of energetic and ecological constraintson avian incubation.     

Experimental manipulation of female tail length did not cause differential allocation by males in the barn swallow

The evolution and maintenance of female ornamentation has attracted increasing attention, because the previous explanation, that is a non‐functional copy of functional male ornamentation, seems insufficient to explain female ornamentation. A post‐mating sexual selection, differential allocation, may be more common than pre‐mating sexual selection, but few studies have investigated differential allocation by males. Here, we studied differential allocation of incubation investment by male barn swallows Hirundo rustica, a model species for the study of sexual selection, because our previous correlative study demonstrated a positive relationship between female tail length and male incubation investment. We manipulated the length of the outermost tail feathers in females after clutch completion and examined whether males adjust incubation investment according to female ornamentation. Because extra‐pair paternity is virtually absent in the study population, we were able to study differential allocation based on the tradeoff between current and future reproductive investments, rather than the tradeoff between current paternal investment and additional mating effort. The experimental treatment had no significant effect on male nest attentiveness, whereas female tail length before manipulation predicted male nest attentiveness. The observed pattern is consistent with differential access; that is, well‐ornamented individuals have greater access to mates with high reproductive (parental) ability, rather than differential allocation during incubation. Alternatively, males can directly assess eggs in their nests, and thus, as seen in other species, males might adjust their incubation investment based on the egg characteristics of long‐tailed females.     

Habituation and habitat changes can moderate the impacts of human disturbance on shorebird breeding performance

Disturbance by humans is widely expected to reduce the reproductive fitness of nesting birds if disturbance reduces nest attentiveness, and unattended eggs experience increased risk of predation or exposure to potentially lethal temperature extremes. Yet, relatively few studies have examined the physiological or behavioural mechanisms whereby disturbance influences reproductive fitness, or the extent to which the costs of disturbance may be reduced through habituation. We compared the behavioural responses, egg temperatures and reproductive success of shore-nesting white-fronted plovers Charadrius marginatus to disturbance at two breeding sites experiencing low versus high human recreational activity, respectively. Daytime nest attentiveness decreased with increasing experimental disturbance at both sites, but this relationship differed between sites; for any given level of disturbance, incubating birds at the more disturbed site had greater nest attentiveness. They achieved this through habituation, allowing a closer human approach before leaving the nest, and returning to the nest faster after a disturbance event. Despite lower average daytime nest attentiveness at the more disturbed site, incubation temperatures did not differ significantly between sites. Nest mortality, mostly by natural mammalian and corvid predators, was significantly lower at the site experiencing high recreational activity. However, chick mortality was significantly greater at the more disturbed site, most likely because of predation by domestic dogs. Chick mortality may have been increased by the habitation of chicks, whose escape responses were much reduced at the more disturbed site. Nonetheless, annual fecundity was substantially higher at the more disturbed site, showing that the overall reproductive fitness of wild birds is not always compromised by human disturbance and urbanization.     

Do extended incubation recesses carry fitness costs in two cavity‐nesting birds?

Because extended incubation recesses, where incubating songbirds are away from nests for periods much longer than usual, occur infrequently, they have been treated as outliers in most previous studies and thus overlooked. However, egg temperatures can potentially fall below the physiological zero temperature during extended recesses, potentially affecting developing embryos. As such, evaluating extended recesses in an ecological context and identifying their possible fitness effects are important. With this aim, we used iButton data loggers to monitor the incubation behavior of female Blue Tits (Cyanistes caeruleus) and Great Tits (Parus major) during two breeding seasons in central Spain. We classified incubation recesses as extended if they were more than four times the mean recess duration for each species. Extended incubation recesses occurred more frequently in 2012 when females exhibited poorer body condition. Female Blue Tits had more extended incubation recesses than female Great Tits and, for both species, more extended recesses occurred at the beginning of the breeding season. Both nest attentiveness and average minimum nest temperature decreased when at least one extended recess occurred. Incubation periods averaged 4 d longer for nests where females had at least one extended recess, potentially increasing predation risk and resulting in lower‐quality nestlings. Overall, our results suggest that extended recesses may be more common among songbirds than previously thought and that, due to their effects on egg temperatures and attentiveness, they could impose fitness costs.     

How avian incubation behaviour influences egg surface temperatures: relationships with egg position,development and clutch size

While understanding heat exchange between incubating adults and their eggs is central to the study of avian incubation energetics, current theory based on thermal measurements from dummy eggs reveals little about the mechanisms of this heat exchange or behavioural implications for the incubating bird. For example, we know little about how birds distribute their eggs based on temperature differences among egg positions within the nest cup. We studied the great tit Parus major, a species with a large clutch size, to investigate surface cooling rates of individual eggs within the nest cup across a range of ambient temperatures in a field situation. Using state‐of‐the‐art portable infrared imaging and digital photography we tested for associations between egg surface temperature (and rate of cooling) and a combination of egg specific (mass, shape, laying order, position within clutch) and incubation specific (clutch size, ambient temperature, day of incubation) variables. Egg surface temperature and cooling rates were related to the position of the eggs within the nest cup, with outer eggs being initially colder and cooling quicker than central eggs. Between foraging bouts, females moved outer eggs significantly more than centrally positioned eggs. Our results demonstrate that females are capable of responding to individual egg temperature by moving eggs around the nest cup, and that the energy cost to the female may increase as incubation proceeds. In addition, our results showing that smaller clutches experience lower initial incubation temperatures and cool quicker than larger clutches warrant further attention for optimal clutch size theory and studies of energetic constraints during incubation. Finally, researchers using dummy eggs to record egg temperature have ignored important elements of contact‐incubation, namely the complexity of how eggs cool and how females respond to these changes.     

Extended incubation recesses by alpine‐breeding Horned Larks: a strategy for dealing with inclement weather?

ABSTRACT Incubating birds can incur high energetic costs and, when faced with a trade‐off between incubation and foraging, parents may neglect their eggs in favor of their own somatic needs. Extended incubation recesses are an example of neglect, but they are often treated as outliers and largely overlooked in studies of incubation behavior. We studied incubation rhythms of Horned Larks (Eremophila alpestris) on Hudson Bay Mountain, British Columbia, Canada, during four breeding seasons. Incubation recesses averaged 10.92 ± 0.38 min (N= 4076 2‐h periods), but we observed 70 extended recesses, ranging from 59 to 387 min in duration, at 35 nests. Although rare (<1% of all daytime recesses), extended recesses occurred in all 4 yr, were longer and more frequent in colder years (60% occurred in the two coldest years), and often occurred during inclement weather (39% occurred during three storm events). Extended recesses did not appear to compensate for long attendance periods because extended recess duration was not correlated with the duration of previous on‐bouts (P= 0.10, N= 70) or the mean on‐bout duration of the previous 2‐h period (P= 0.36, N= 70). Rather, extended recesses seemed to reflect a shift in parental investment away from their eggs and toward self‐maintenance when faced with energetically stressful conditions. Extended recesses may have reduced embryo viability; egg‐hatching rates were 91 ± 2.4% for nests where females did not take extended recesses and 81 ± 4.2% for nests where females did take extended recesses (P= 0.02, N= 56 nests). Extended recesses during incubation are rare events, but they may represent an important mechanism that allows birds to breed successfully in energetically challenging conditions.