Nestling Growth Rates Research Articles

The interplay among breeding timing, brood size, food quantity, and nestling growth rate in the Eurasian eagle owl (Bubo bubo)

Abstract Optimal clutch size theory predicts a trade-off between egg number and fledgling body mass, potentially affecting their survival rate. Yet, only a few studies have directly linked clutch or brood size to energy (food), nestling growth rate, and timing of breeding. We studied the relationship among all these variables in the Eurasian eagle owl. Of 150 eggs laid in 48 nests, 119 hatched and 117 nestlings fledged, indicating low nestling mortality. The number of eggs, hatchlings and fledglings (possibly indicating territory quality) decreased with ordinal date. The total amount of food brought to the nest increased with brood size, but the average amount per nestling decreased. Nestling growth rate (and thus probably fledgling body mass) was negatively correlated with brood size. A trade-off between brood size and fledgling survival may lessen the benefit of occupying food-rich territories. However, we suggest that fledglings from large broods, despite their relatively low body mass, may have higher survival rates owing to their relatively early fledging. This may be due to: (1) higher prey abundance in late spring compared with late summer and (2) a longer period before entering the cold season. Variation in brood size may therefore represent a set of strategies linked to prey abundance.

Latitudinal and elevational variation in the reproductive biology of house wrens, Troglodytes aedon.

While cross-species comparisons of birds suggest that as latitude decreases or elevation increases, clutch size decreases and the duration of developmental stages and parental attentiveness increases, studies comparing populations of the same species are rare. We studied populations of house wrens, Troglodytes aedon, at high and low elevations in California and Costa Rica, collecting data on clutch size, the duration of incubation and nestling periods, parental attentiveness, nestling growth rate, and nesting success. Our data support results from cross-species comparisons, but also revealed unanticipated results from low elevation temperate zone house wrens in the southwest. This population had prolonged incubation and nestling periods similar to those found in the tropics. We also found that temperate zone females, especially those at our higher elevation site, spent more of their day incubating than did tropical females. Nest temperature at our high elevation temperate zone site was higher than that at all other tropical sites. Age at fledging did not differ between sites. Total feeding rates per chick and male feedings per chick did not vary between sites. Nest success rates showed the predicted effect of latitude, but not the predicted effects of elevation. Our results extend low elevation house wren research into the southwestern US and contribute the first intraspecific elevational comparison in the Neotropics. Data from our low elevation southwestern site present a unique suite of life history traits that align more with tropical house wrens, although with a larger clutch size, and point to food limitation and/or high predation pressure as being possible drivers of some of these differences. These results highlight the need for additional studies of house wrens and other broadly distributed species at a more diverse array of sites to better understand which forces drive the evolution of different life history strategies across major biogeographical gradients.

Nestling growth rate and food consumption increases under experimentally prolonged daylength in a New World sparrow

When evaluating avian reproduction, life history theory examines the trade‐offs between parental effort, the number and size of offspring, and the rate of nestling development. The growth rates and body sizes of developing birds vary geographically and can diverge with both latitude and migratory strategy. In terms of offspring size, growth rate can deviate in nestlings of the same or similar species due to the correlated influences of weather events, predation pressure, food availability, number of nestmates and parental provisioning. Furthermore, a longer photoperiod for species nesting at higher latitudes increases the duration over which a nestling can be fed each day, and increased nestling provisioning has been positively correlated with growth rate. Whether the amount of time a bird is fed during development drives this variation in growth rate and morphology is unknown. By removing supplemental environmental stressors (e.g. weather, predation) and standardizing feeding rate and environment, we explored the influence of daily duration of nestling provisioning on dark‐eyed junco Junco hyemalis nestlings. We hand‐reared 65 chicks of a sedentary junco subspecies J. h. carolinensis under both their natural photoperiod and the longer photoperiod of a closely related migratory subspecies J. h. hyemalis and compared growth rate, mass, morphology and the amount of food consumed. Average growth rate, fasted mass, wing length and total daily food consumption were all greater in birds hand‐reared under the longer, more northern photoperiod treatment. These findings suggest that increased daily photoperiod at higher latitudes may allow for greater total food provisioning and thus may play a role in the ability of parents in compressed breeding seasons to produce high quality offspring. This points to a trade‐off between provisioning effort and nestling growth rate in lower latitude (shorter photoperiod) populations and points to an important role of developmental plasticity on growth rate and morphology.

Year-round weather alters nest-provisioning rates in a migratory owl.

As global temperatures and precipitation become more extreme, habitat specialists are at particular risk of being pushed past their environmental tolerance limits. Flammulated Owls (Psiloscops flammeolus) are small migratory owls that breed in temperate conifer forests of western North America. Their highly specialized nesting and foraging requirements make them indicators of ecosystem health. Using 17 years of nest observations, we investigated how annual weather patterns affected Flammulated Owl nesting and foraging behaviors during the breeding season. We used generalized linear models with a changepoint parameter to evaluate nest provisioning and nestling growth rates in years of extreme temperature and precipitation. We also evaluated how adult mass, division of labor, and productivity varied based on precipitation and temperature. Compared to wet and warm years, adults made more frequent prey deliveries to nestlings in dry and cold years, particularly early in the night and early in the season, and they experienced earlier changepoints in these years. We found a significant effect of temperature on the number of fledglings in broods, but weather did not affect other variables including productivity, nestling growth rates, adult masses, and division of labor. Our findings suggest that extreme annual weather patterns influence insect prey availability during the Flammulated Owl breeding season, forcing adults to work harder to provision for nests during dry and cold years. While productivity and nestling growth did not vary between years, these may incur a long-term tradeoff in adult survival.

Immunity and Growth Plasticity of Asian Short-Toed Lark Nestlings in Response to Changes in Food Conditions: Can It Buffer the Challenge of Climate Change-Induced Trophic Mismatch?

Passerine nestlings frequently suffer from sub-optimal food conditions due to climate change-induced trophic mismatch between the nestlings and their optimal food resources. The ability of nestlings to buffer this challenge is less well understood. We hypothesized that poor food conditions might induce a higher immune response and lower growth rate of nestlings, and such physiological plasticity is conducive to nestling survival. To test this, we examined how food (grasshopper nymphs) abundance affects the expression of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), interleukin-1 β (IL-1β) genes, plasma IGF-1 levels, body mass, and fledging rates in wild Asian short-toed lark (Alaudala cheleensis) nestlings. Linear mixed models revealed that nymph biomass significantly influenced the expression of IFN-γ, TNF-α, and IL-1β genes, and the level of plasma IGF-1. The expressions of IFN-γ, TNF-α, and IL-1β genes were negatively correlated with nymph biomass and plasma IGF-1 level. Plasma IGF-1 level, nestling body mass growth rate, was positively correlated with nymph biomass. Despite a positive correlation between the nestling fledge rate and nymph biomass, more than 60% of nestlings fledged when nymph biomass was at the lowest level. These results suggest that immunity and growth plasticity of nestlings may be an adaptation for birds to buffer the negative effects of trophic mismatch.

Insular nestling growth and its relationship to parental care effort in Silvereyes, Zosterops lateralis

ABSTRACT The rate at which avian offspring grow can have consequences for survival and reproductive output as an adult and is known to vary widely among and within species. This variation is thought to be an adaptive response to cope with environmental variation. The principal environmental factors affecting growth are food availability and predation risk, predominantly acting as constraints on parental care. Islands pose an interesting system to explore growth rate dynamics, because the characteristic insular features of high population densities and depauperate predator diversity translate into a potentially food limited environment with low predation risk. Insular environments typically produce populations with slower life history strategies and larger body size in small-bodied species, features that are likely to be mediated by growth rate. We describe the nestling growth of an insular population of Silvereyes and how it relates to parental size and parental care. Neither parental size nor parental care explained insular nestling growth rate, even though food acquisition is thought to underpin avian growth rates. This could be due to a mismatch between acquisition and allocation of resources by nestlings. Compared to a small number of mainland nestlings, the island growth curve asymptotes were significantly larger and inflection points much later, but insular growth rates were only marginally slower. This is in line with proposed insular adaptations required to produce larger body size on islands, however understanding the mechanism underlying this pattern will require data on the relationship between food quality and acquisition, and physiological allocation of resources within individuals.

Tolerability of Atovaquone-Proguanil Application in Common Buzzard Nestlings.

Differences in drug tolerability among vertebrate groups and species can create substantial challenges for wildlife and ex situ conservation programmes. Knowledge of tolerance in the use of new drugs is, therefore, important to avoid severe toxicity in species, which are both commonly admitted in veterinary clinics and are of conservation concern. Antimalarial drugs have been developed for use in human medicine, but treatment with different agents has also long been used in avian medicine, as haemosporidian infections play a major role in many avian species. This study investigates the effects of the application of atovaquone-proguanil (Malarone®, GlaxoSmithKline) in common buzzards (Buteo buteo). The potential effects of treatment on body condition, growth rate, and chemical blood parameters of nestlings were assessed. All individuals survived the treatment, and no effects on body condition, growth rate, and chemical blood parameters were observed. Our results suggest the tolerability of Malarone® in common buzzards at a single dose of on average 11 mg/kg body weight. For its safe use, we recommend further studies to determine pharmacokinetics in different avian species as well as to assess the effects of repeated treatment.

NOTES ON THE NESTLING BIOLOGY OF THE GOLDEN-WINGED MANAKIN (MASIUS CHRYSOPTERUS)

A complete nesting information is available for 7.8% of the Manakin species; however, most of this information is fragmented and available mainly for lowland species. Hence, nesting information for highland species is scattered. Our study presents nesting information on a cloud forest Manakin species, the Golden-winged Manakin (Masius chrysopterus), which is distributed from western Colombia to northern Peru between 1000 and 2300m. We monitored 10 nests, from February through July in 2014 and 2015 at Parque Nacional Natural Tatamá, Colombia. We describe the nest, egg, and nestling, and provide information on incubation behavior and nestling feeding. The cup nest was similar to those found in most manakins. Eggs were creamy with brown spots concentrated at the base and measured 8.70± 0.89mm x 13.30 ± 0.39mm. The nestling growth rate (K) was 0.38. The incubation and nestling period were 22 and 16 days, respectively. The female conducted 70 off-bout trips day-1 that lasted on average 8.24 ± 5.44min, with 78% nest attentiveness. This study provides the most complete nesting data for a cloud forest manakin. Overall, M. chrysopterus incubation and nestling period are longer when compared to other manakin species. But the nest structure and composition, and eggs coloration concurred with other species.

A 24-year investigation of the reproductive ecology of the Edible Dormouse (Glis glis)

The Edible Dormouse is a non-native rodent introduced to the Chilterns, UK, in 1902. It shows extreme annual variation in breeding; either having one litter per year or, in some years, failing to breed at all. Despite this slow reproductive rate compared to other rodents, its population is increasing, and has spread beyond the anticipated landscape barriers. Communal nesting is sometimes observed. This study aims to characterise the reproduction parameters over time, including from communal breeding. Based on a population of >11,000 PIT-tagged individuals, 600 litters and 4000 nestlings at our Chilterns study site over 24 years, we show the best fit of the number of new-borns is an increasing exponential. Monthly weight of nestlings also increased over the 24 years, while annual reproduction rate, litter size and nestling growth rates remained unchanged. Litter size decreased from 6.6 new-borns in August to 4.3 in October, indicating an average death rate of 37% in the first two months of life. Preliminary analysis suggests a small decrease in death rate over the years. Average growth rate of nestlings was c.100% of birth weight per week in their first month, but then slowed. We also examined evidence of kinship between nest sharers and investigated whether this, or communal breeding in general, promotes offspring survival. Our results will provide a deeper insight into the factors that drive the reproductive success of this invasive species and enable investigation of the effect of climatic variables on the number, survival and growth rate of nestlings.

Reliability of steatocrit as an indicator of intestinal health in young birds – Relationships with morphology and growth rate of canary Serinus canaria nestlings

Intestinal health and capacity to efficiently absorb nutrients from diet, including fat, has been recently suggested as a promising physiological health indicator in wild birds, due to its association with gut parasitism and feather coloration. However, little information is available about the sources of variation of non-absorbed fat in birds’ faeces, measured by the acid steatocrit technique, and particularly in nestling birds. We assessed steatocrit in captive nestling canaries Serinus canaria and evaluated if it was affected by breed and its relationship with growth (linear growth rate, LGR) and body mass. We also assessed the presence of coccidia infections. Steatocrit differed significantly between day 9 and 14 of the nestling period, being lower when nestlings were 14 days old. Age must be taken into account when assessing steatocrit in young birds; this variation may be due to a development of the digestive system with age or the amount of fat provided later in the nestling period being more adequate to the nestlings’ needs. Steatocrit was higher in nestling canaries from yellow lipochromic than red lipochromic breeds. No coccidia infections were detected. Steatocrit did not affect LGR, but steatocrit measured at day 9 was positively related with body mass at day 14. The positive relationship between steatocrit and body mass in canary nestlings suggests that nestlings in breeding facilities may be fed a larger amount of fat than that they can absorb. This physiological assessment of intestinal health may be a better general health indicator in wild adult birds exposed to a higher level and diversity of parasites.

Delayed timing of breeding attempts, but not time lost to nest construction, reduces the annual reproductive output of the Eastern Phoebe (Sayornis phoebe)

For many birds, nest construction is a costly aspect of parental care, trading finite energetic resources between parental care and self-maintenance. For multi-brooded organisms with short breeding seasons, such as migratory passerines, repeated nest construction could be especially costly if the activity delays the onset of breeding attempts. Earlier studies on passerines that reuse nests between breeding seasons suggested that time lost to initial nest construction reduces seasonal reproductive output. However, costs associated with building new nests between breeding attempts, within the same breeding season, have largely been ignored. Here, we experimentally removed first nests, after fledging or failing, of Eastern Phoebes ( Sayornis phoebe), to evaluate how the annual onset of breeding and nest construction between breeding attempts affected parental investment into second attempts. We found that first egg laying date negatively predicted the probability of second breeding attempts, but experimental treatment (first nest removal vs. control) did not. Neither first egg laying date nor treatment statistically influenced any of the reproductive traits in second breeding attempts (clutch size, nestling body condition, and nestling growth rate). We conclude that in this species, second breeding attempts are limited by the initial onset of seasonal reproduction, and not by time lost to nest construction between breeding attempts.

Breeding records of Leptotila rufaxilla (Aves: Columbidae) in southwestern Brazilian Amazon with notes on nesting in some regions of occurrence

We present new aspects of breeding biology of Gray-fronted Dove Leptotila rufaxilla, from five nests found between 2012 and 2014 in a lowland forest fragment in southwestern Brazil. The nests simple/platform shape were built at a mean height of 1.90 m above ground. The clutch size was two eggs white and elliptic, incubated for 15 days (based on three nests). We recorded predation in two nests still in incubation phase. Minimum hatch weight of nestlings was 10 g and young fledged with a mean mass of 56 g. The constant growth rate (K) of nestlings was 0.40 with a growth asymptote of 60.7 g. Daily survival rate, Mayfield and apparent nesting success in the incubation period was 90, 20 and 56%, respectively, while in the nestling period were all 100%. Our data and the contribution of citizen science showed that L. rufaxilla breeds over the year, mainly in the rainy season, both in southwestern Amazonia and in other regions of occurrence.

Breeding biology and biometrics of Myiozetetes c. cayanensis (Aves: Tyrannidae) in southwest Brazilian Amazonia with breeding season in Brazil

Our study provides information on the breeding and biometrics of Rusty-Margined Flycatcher Myiozetetes cayanensis in southwest Brazilian Amazonia. Myiozetetes cayanensis is distributed from Central America until north of South America. We made observations on reproduction and captures of this species in a terra firme forest fragment in the state of Acre, between 1999 and 2020 and we evaluated the breeding season in Brazil through citizen science data. We monitored nine nests between 2012 and 2020, built at a mean height of 1.8 m above ground. Clutch size was two, three or four eggs, incubated for 15 days. We monitored the development of six nestlings: minimum hatch weight was 2 g and young fledged with a mean mass of ca. 25.5 g. The constant growth rate (K) of nestlings was 0.18 with a growth asymptote of 22.8 g. Daily survival rate was 90% and 100% during the incubation and nestling periods, respectively. The Mayfield success in the incubation and nestling periods was 20 and 100%, respectively. Apparent nesting success in the incubation and nestling periods was 46 and 100%, respectively. We recorded a minimum longevity of 2 years, nine months and 26 days. The subspecies M. c. cayanensis start to nest mainly between the dry and rainy season in Brazil, overlapping with the molt period in southwest Amazonia.

First nest records, nestling growth and morphometrics of Dendroplex picus peruvianus (Aves: Dendrocolaptidae) in southwestern Brazilian Amazon

We reported the first data on the breeding and growth in Dendroplex picus peruvianus from a forest fragment in southwestern Amazonia. We observed and netted this species between 1999 and 2019. We found two active nests in 2012 and 2013, but we monitored only one. Clutch size was two eggs, incubated for 16 days. The constant growth rate (K) of nestlings was 0.31 with a growth asymptote of 46.3 g. We recorded a longest minimum longevity of eight years. Our records showed that D. p. peruvianus breeds mainly in the rainy season (September–March) overlapping with the molt period.

Direct and indirect effects of high temperatures on fledging in a cooperatively breeding bird

Abstract High temperatures and low rainfall consistently constrain reproduction in arid-zone bird species. Understanding the mechanisms underlying this pattern is critical for predicting how climate change will influence population persistence and to inform conservation and management. In this study, we analyzed Southern Pied Babbler Turdoides bicolor nestling survival, daily growth rate and adult investment behavior during the nestling period over three austral summer breeding seasons. High temperatures were associated with lower body mass, shorter tarsi, and reduced daily growth rates of nestlings. Our piecewise structural equation models suggested that direct impacts of temperature had the strongest influence on nestling size and daily growth rates for both 5-day-old and 11-day-old nestlings, followed by temperature-related adjustments to provisioning rates by adults. Rainfall and group size influenced the behavior of provisioning adults but did not influence nestling growth or survival. Adjustments to adult provisioning strategies did not compensate for direct negative effects of high air temperatures on nestling size or daily growth rates. Detailed mechanistic data like these allow us to model the pathways by which high temperature causes nest failure. In turn, this could allow us to design targeted conservation action to effectively mitigate climate effects.

Poor prey quality is compensated by higher provisioning effort in passerine birds

In altricial avian species, nutrition can significantly impact nestling fitness by increasing their survival and recruitment chances after fledging. Therefore, the effort invested by parents towards provisioning nestlings is crucial and represents a critical link between habitat resources and reproductive success. Recent studies suggest that the provisioning rate has little or no effect on the nestling growth rate. However, these studies do not consider prey quality, which may force breeding pairs to adjust provisioning rates to account for variation in prey nutritional value. In this 8-year study using black-capped (Poecile atricapillus) and boreal (Poecile hudsonicus) chickadees, we hypothesized that provisioning rates would negatively correlate with prey quality (i.e., energy content) across years if parents adjust their effort to maintain nestling growth rates. The mean daily growth rate was consistent across years in both species. However, prey energy content differed among years, and our results showed that parents brought more food to the nest and fed at a higher rate in years of low prey quality. This compensatory effect likely explains the lack of relationship between provisioning rate and growth rate reported in this and other studies. Therefore, our data support the hypothesis that parents increase provisioning efforts to compensate for poor prey quality and maintain offspring growth rates.

The time-activity budgets of breeding Blue Swallows Hirundo atrocaerulea and the effects of weather on nestling growth

The Blue Swallow is an intra-African migrant that breeds in its fragmented range from South Africa to southern Tanzania, from October to March annually. The birds migrate north and are on their non-breeding range in NE DRC, Uganda, NW Tanzania and W Kenya, from April to September annually. The global Blue Swallow population, estimated at <1 500 pairs, is classified as ‘Vulnerable’, because of its small and declining population. Only the female Blue Swallow incubates the eggs and broods the nestlings for the first nine days after they have hatched from the eggs. The growth rate of Blue Swallow nestlings is reduced by adverse weather conditions characterised by low temperatures (<14 °C), 3–4 consecutive days of fog and intermittent rainfall. In the Blue Swallow Natural Heritage Site (25°36′ S, 30°45′ E), food shortages, because of three or more consecutive days of adverse weather conditions resulted in Blue Swallows shifting entirely to self-maintenance by abandoning eggs and nestlings and attempting to breed again when weather conditions improved. The post-fledging survival of the nestlings affected by adverse weather conditions is reduced. The reason is that at the time of fledging the mass of these nestlings was below the mean mass of the adults and because the mass of nestlings developing under good weather conditions is equal to or greater than the mean mass of the adult birds. Circumstantial evidence suggests that Common Fiscal Lanius collaris may be the predator of Blue Swallow eggs and nestlings. Adult longevity and the breeding success of Blue Swallows may have been reduced by adverse weather affecting their entire meta-populations in the small and isolated patches of suitable habitat remaining for the birds. These characteristics of the Blue Swallow meta-populations may be contributing to their continued decline.

An anti-narcolepsy drug reveals behavioral and fitness costs of extreme activity cycles in arctic-breeding songbirds.

Sleep loss impairs cognitive function, immunological responses and general well-being in humans. However, sleep requirements in mammals and birds vary dramatically. In circumpolar regions with continuous summer light, daily sleep duration is reduced, particularly in breeding birds. The effect of an anti-narcolepsy drug (modafinil) to putatively extend wakefulness was examined in two species of closely related arctic-breeding passerine birds: Lapland longspurs (Calcarius lapponicus) and snow buntings (Plectrophenax nivalis). Free-living adult males were implanted during the nestling phase on day 4 (D4; 4 days post-hatching) with osmotic pumps containing either vehicle or modafinil to extend the active period for 72 h. Nestlings were weighed on D2 and D7 to measure growth rates. Additionally, focal observations were conducted on D6. Male longspurs receiving modafinil made fewer feeding visits and spent less time at the nest but tended to spend more time near the nest than controls. We observed no change in longspur nestling growth rates, but fledging occurred significantly later when males received modafinil, suggesting a fitness cost. In contrast, modafinil had no measurable impact on male or female snow bunting behavior, nestling growth rates or time to fledging. We suggest male longspurs compromise and maintain vigilance at their nests in lieu of sleeping because of the increased predation risk that is characteristic of their tundra nesting habitat. Snow buntings are cavity nesters, and their nests do not require the same vigilance, allowing males to presumably rest following provisioning. These life-history differences between species highlight the role of predation risk in mediating behavioral modifications to prolonged wakefulness in arctic-breeding songbirds.

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 (&gt; 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.

Can oceanic prey effects on growth and time to fledging mediate terrestrial predator limitation of an at‐risk seabird?

AbstractMost seabird species nest colonially on cliffs or islands with limited terrestrial predation, so that oceanic effects on the quality or quantity of prey fed to chicks more often determine nest success. However, when predator access increases, impacts can be dramatic, especially when exposure to predators is extended due to slow growth from inadequate food. Kittlitz’s Murrelet (Brachyramphus brevirostris), a rare seabird having experienced serious declines, nests solitarily on the ground in barren, often alpine areas where exposure to predators is generally low. Nestling growth rates are exceptionally high and nestling periods very short relative to other Alcidae. This strategy reduces duration of exposure to predators, but demands adequate deliveries of high‐energy prey. In an area where foxes can access nests, we investigated whether varying energy content of prey fed to chicks could alter growth rates and resulting duration of predator exposure, and whether prolonged exposure appreciably reduced nest success. From 2009 to 2016, we monitored 139 nests; 49% were depredated (almost all by foxes) and 25% fledged. Prey fed to nestlings were 80% Pacific sand lance (Ammodytes personatus) and 19% capelin (Mallotus villosus), with capelin having 2.3× higher energy content per fish. In a year of slow chick growth, increased sand lance energy density of 31% (4.29–5.64 kJ/g, within published values), or increased proportion of capelin in the diet from 5.6% to 27.2%, would have allowed maximum chick growth. Maximum growth rates were attainable by delivering only 1.9 capelin/d versus 5.5 sand lance/d. Slow growth increased time to fledging by up to 5 d, decreasing survival by 7.7% (0.142–0.131). Breeding propensity of Kittlitz’s Murrelet averages only 20%, so even small changes in nest success could affect populations. Although nest success was limited mainly by predation, oceanic effects on prey quantity and quality had overriding impacts in one year (2015 heat wave), and small but substantive effects in other years by mediating exposure to predation. Climate warming that decreases availability of high‐energy forage fish, or increases expansion of predators into nesting habitats, may disproportionately affect this sensitive species and others with predator‐accessible nests and demands for energy‐rich prey.