Egg Temperature Research Articles

Fuzzy Control of Water Level and Temperature in Fish Eggs Breeding Tank with Different Sensor Inputs

In this paper fuzzy logic principles are used to control the level and temperature of water in fish eggs breading tank. The control task aims to keep the water level and the water temperature in a tank within certain ranges, the temperature due to Newton’s law of cooling would drop down, and to keep it within limits, hot water is added, and cold water is drained. Sensors for temperature and level are used to give fuzzy input to the fuzzy controller which outputs the amount of opening in the two control valves.

Effects of different step-wise temperature increment regimes during egg incubation of Atlantic cod (Gadus morhuaL.) on egg viability and newly hatched larval quality

We carried out an experiment to determine how rapidly the early incubation temperature of Atlantic cod eggs can be increased without affecting normal embryonic development and hatching. Atlantic cod eggs were incubated at a constant low temperature (4.5 ± 0.5°C; T5 – control) and four temperature increment treatments where the temperatures were increased stepwise from 4.5°C at zygote stage to 9.5 ± 05°C (T1-8 h, T2-32 h, T3-64 h and T4-96 h). Embryonic cell symmetry, embryonic mortality, hatching success and larval skeletal abnormalities, length and yolk sac volume were recorded. Larval samples were also taken at hatch for histological analysis. Except for higher egg mortality and lower hatching success in the T1, the differences among experimental groups were minor. Cell asymmetries and embryo mortalities were not significantly different between the control and T2–T4 treatment groups. Control larvae were significantly longer and had smaller yolk reserves at hatch than T1–T4 larvae and larvae from T2 had the largest yolk reserves. Tissue and organ histology of hatched larvae were similar. Considering embryonic cleavage pattern, hatching success and larval morphology and histology, a gradual increment of temperature in 32 h seems to be the better choice for future developmental programming studies in Atlantic cod.

Microclimate of Tree Cavities Used by Great Tits (Parus Major) in a Primeval Forest

Altricial birds nesting in places with a favourable microclimate would be able to maintain the proper temperature of eggs or nestlings with less effort and thus reproduce more successfully. Tree cavities provide relatively safe nesting sites, but their microclimate is hardly known. Here we present the first data on air temperature and humidity in natural cavities used by Great Tits nesting in protected primeval forest in the Białowieża National Park (Eastern Poland). We checked what microclimatic conditions existed in cavities selected by Great Tits, how the construction of a nest changed the microclimate in a cavity and to what extent cavity localisation and cavity dimensions modified the microclimate of the breeding cavities. Great Tits used cavities in the living trees which were characterised by cool but relatively stable temperatures and very high relative humidity. Such conditions appear to be typical for cavities in living trees in general. Cavities with Great Tit broods were warmer and drier that the unused ones. The microclimate did not appear to constitute the major factor determining Great Tit usage of cavities in living trees, but it could exert a modifying effect on the pattern of cavity use by them. By choosing cavities of appropriate dimensions and placing the nest at an appropriate distance from the entrance, Great Tits could modify the cavity microclimate. However, their options were probably constrained by necessity to meet other important requirements, such as nest safety and illumination.

Parental Behavior Controls Asynchronous Hatching, but Not Incubation Period, in the Magellanic Penguin: A Commentary on Rebstock and Boersma (2011)

Abstract. Rebstock and Boersma (2011) recently explored variation in the temperature and incubation period of eggs within clutches of the Magellanic Penguin (Spheniscus magellanicus). They defined incubation period as “the time from the laying of an egg to its hatching” and concluded that parental behavior explained why the incubation period of second eggs was shorter than that of first eggs and controlled asynchronous hatching. While we agree that parents influenced asynchronous hatching by delaying the onset of incubation, we argue that their conclusions are based on an unconventional definition of incubation period. They included the period before the delayed onset of incubation in the incubation period, which leads to confusion. We state that the incubation period cannot include the time before the (delayed) onset of incubation when parents are not warming the eggs. As regards this latter and widely accepted definition, Rebstock and Boersma (2011) provided a large dataset showing that incubation consi...

Ontogeny of constitutive immunity: maternal vs. endogenous influences

SummaryVariation in ontogeny and strength of immune defence mechanisms can be integrally related to variation in life‐history strategies and determined by trade‐offs during development. However, little is known about the ontogeny of immune function in wild birds, especially in altricial birds and in a comparative context across altricial species with diverse life‐history strategies.In this study, we examined the ontogeny of constitutive immunity in a group of 22 passerine species sampled in tropicalVenezuela and north temperateArizona.Our results show activity of constitutive components of the immune defence at 1–3 days posthatching and an increase in immune activity with age. Interspecific variation in immune activity at hatching was mainly explained by extrinsic factors mediated by the mother (egg size and egg temperature), suggesting an important role of maternal effects on offspring immunity at hatching. In contrast, the increase in agglutination activity with age suggests that immune function in older nestlings reflects intrinsic development. The increase in immune activity was greater in species that hatched with lower initial levels, and was somewhat negatively related to growth rate across species.Our results suggest slower intrinsic development of immune function may be compensated by larger maternal contributions. Slower intrinsic development of immune function, in turn, may reflect a trade‐off with faster somatic growth. Our study highlights the importance of both maternal (extrinsic) and endogenous (intrinsic) contributions to variation in immune function across altricial species that may reflect an important axis of developmental strategies.

Elevated corticosterone levels and severe weather conditions decrease parental investment of incubating Adélie penguins

Corticosterone, the main stress hormone in birds, mediates resource allocation, allowing animals to adjust their physiology and behaviour to changes in the environment. Incubation is a time and energy-consuming phase of the avian reproductive cycle. It may be terminated prematurely, when the parents' energy stores are depleted or when environmental conditions are severe. In this study, the effects of experimentally elevated baseline corticosterone levels on the parental investment of incubating male Adélie penguins were investigated. Incubation duration and reproductive success of 60 penguins were recorded. The clutches of some birds were replaced by dummy eggs, which recorded egg temperatures and rotation rates, enabling a detailed investigation of incubation behaviour. Corticosterone levels of treated birds were 2.4-fold higher than those of controls 18days post treatment. Exogenous corticosterone triggered nest desertion in 61% of the treated birds; consequently reducing reproductive success, indicating that corticosterone can reduce or disrupt parental investment. Regarding egg temperatures, hypothermic events became more frequent and more pronounced in treated birds, before these birds eventually abandoned their nest. The treatment also significantly decreased incubation temperatures by 1.3°C and lengthened the incubation period by 2.1days. However, the number of chicks at hatching was similar among successful nests, regardless of treatment. Weather conditions appeared to be particularly important in determining the extent to which corticosterone levels affected the behaviour of penguins, as treated penguins were more sensitive to severe weather conditions. This underlines the importance of considering the interactions of organisms with their environment in studies of animal behaviour and ecophysiology.

Partial incubation and its function in great tits (Parus major)—an experimental test

In many bird species, females incubate the eggs for short periods before clutch completion. The role of such partial incubation and the effective egg temperatures attained are controversial. Possible functions depend on whether temperatures reach the critical values required for embryogenesis and include the protection of the clutch from predators, brood parasites, and environmental factors; inhibition of bacterial growth on eggs; control of hatching asynchrony; or energy saving by parents. In this study, in a natural population of great tits, we first investigated the occurrence and extent of partial incubation, and second, we evaluated some potential functions by experimental simulation of the observed patterns of partial incubation. We found that egg temperatures during partial incubation were clearly raised above the physiological zero temperature for embryo development. Simulation of partial incubation did not affect any breeding parameters or nestling morphological traits compared with controls. It suggests that partial incubation with temperatures above the minimum temperature for embryo development does not serve to increase the variation in nestling morphology and thus competitiveness, in particular, does not increase hatching asynchrony within brood as one of its currently most discussed functions. Key words: egg temperatures, hatching asynchrony, maternal effects, nestling morphology, Parus major, phenotypic variation. [Behav Ecol]

Ambient Temperature And Nest Temperature Variation In Enclosed Nests (Spanish Sparrow) And Open-Cup Nests (Iberian Azure-Winged Magpie)

Abstract Temperature plays a central role in the life of birds, especially during egg incubation and nestling thermal brooding. I investigated nest temperature variation relative to ambient temperature during incubation in an enclosed nest-builder species (Spanish sparrow Passer hispaniolensis) and an open-cup nest-builder species (Iberian azure-winged magpie Cyanopica cooki). The data for empty enclosed nests showed that the nest structure acted as a temperature buffer which reduced the impact of night-time temperature variation within the nest. The buffer effect was reduced as ambient temperature increased at dawn. The presence of an adult increased the difference between nest temperature and ambient temperature, and dissociated its variation from the ambient temperature variation. The enclosed nest also retained the body heat released by an adult in the nest. Both effects had a positive effect on the temperature balance in the nest. By contrast, open-cup nest temperature was more affected by the ambient temperature, although it did not affect the egg temperature directly. Thus the absence of an incubating parent would endanger the hatchability in open-cup nests more rapidly than in enclosed nests. The life histories of the investigated species correspond to these findings, i.e. a more pronounced presence of the female in the Iberian azure-winged magpie nests.

The Woodpecker's Cavity Microenvironment: Advantageous or Restricting?

We studied the nesting biology of the Syrian woodpecker ( Dendrocopos syriacus) in Israel, emphasising its physiological aspects and the environment of the tree hole nest cavity (~ 2 litres in volume). Eggs (mean mass = 5.4 ± 0.4 g SD) are laid once a day during April and May to produce a mean clutch size of four (range 3-5). Active incubation starts after the last egg is laid and lasts 11 days. Both hatching and fledging are spread over 2-3 days. Parents share incubation during the day but only males incubate at night. Both parents share the feeding of the nestlings equally. Males occupy and guard the empty nest at night all year round. Incubation and fledging periods add up to a normal fledging time for the species. The young are fed by their parents outside the nest for another month. Mean egg temperature was not significantly different between day and night, averaging 34.2°C (± 4.3 SD). Mean egg water loss was 1.4 % d−1 of the initial egg mass prior to the onset of incubation and 0.5% d−1 during incubation. The extrapolated total water loss of the eggs was 13.1% at the end of incubation. This indicates a good match of cavity humidity and the water vapour eggshell conductance of 1 mg·(d Torr)−1 (=100 mg·(d kPa)−1), where, in spite of the higher egg temperature during active incubation, the egg water loss rate is reduced due to the presence of the incubating parent. Gas composition at the bottom of the nest initially decreased by ~ 1.75 % for O2 whereas CO2 increased by ~ 1.20 %, due to clutch activities until the nestlings were about 15 days old. There was little change in nest gas composition between 15 and 22 days of rearing. From that time on until fledging O2 concentration increased and CO2 decreased due to nestlings’ up and down activity in the nest shaft and the fact that they fledge asynchronously at the age of 26 days.

Magellanic Penguin (Spheniscus magellanicus) Embryos Tolerate High Temperature Variations and Low Temperatures during Incubation

Maintaining appropriate developmental temperatures during avian incubation is costly to the parents, so embryos may experience pronounced variations in temperature that can lead to embryo mortality and extended incubation periods, or that could affect the offspring phenotype in several bird species. The egg temperatures (N = 28 eggs) of free-living Magellanic Penguins (Spheniscus magellanicus) were recorded in a breeding colony in Puerto Deseado, Santa Cruz, Argentina. Three nests had atypical incubation patterns. Two nests experienced high temperature drops (average = 11.7°C, minimum = 6.5°C, duration = 9 h) and another nest had a broad daily temperature range (max-min), i.e. 13.9 ±0.9°C for the first egg and 14.1 ±0.8°C for the second egg (range = 8-22°C during egg laying and 18–37°C during advanced incubation). Thermal anomalies during incubation did not affect the embryonic viability, hatchling mass or fledging success. The survival of embryos despite these atypical incubation patterns may be an adaptive mechanism during the harsh weather conditions normally experienced by eggs throughout incubation.

Nest attentiveness in several Neotropical suboscine passerine birds with long incubation periods

Many species of tropical birds have prolonged incubation periods compared to other tropical species and to most species in temperate latitudes. One hypothesis for prolonged incubation is that these tropical species reduce nest attendance to minimize the risk of predation. The resulting decrease in average egg temperature would reduce embryo growth rate and lengthen the embryo development period. We sampled six species of Neotropical, lowland, inner forest antbirds (Thamnophilidae) and flycatchers (Tyrannidae) with average incubation periods between 17.9 and 23.3 days. Estimated total integrated 24-h nest attendance between clutch completion and hatching ranged between 14.2 and 19.5 days, representing 71–84 % of the incubation periods. Because total nest attendance in these species exceeded the incubation periods of most small passerine birds in temperate latitudes, and because average nest attendance per day did not differ substantially between these tropical species and temperate species, reduced nest attendance does not appear to cause their prolonged incubation periods. Instead, these extended egg periods likely reflect slower embryonic growth and development at a given egg temperature. Prolonged incubation can increase time-dependent mortality in the nest, which would require an increase in either post-fledging survival or adult reproductive success to favor a slow-growth evolutionary strategy. Mechanisms underlying the postulated trade-off between incubation period length and individual quality merit further investigation.

Physiological relationships of the early posthatch performance of broilers to their embryo and eggshell characteristics

Relationships between physiological parameters of early posthatch chicks with their corresponding egg and embryo parameters were examined in progeny of young broiler breeders. Four hundred and 80 broiler hatching eggs that were obtained from a 29-wk-old Ross 308 breeder flock were incubated on 8 replicate tray levels of an incubator until hatch. Between 10.5 and 18.5 d of incubation, internal (T(emb)) and external (T(ext)) egg temperatures were recorded twice daily using temperature transponders. Beginning at 18.5 d, the eggs were individually monitored for hatch every 12 h. Average T(emb), T(ext), and average daily incubational egg weight loss (EWL) for the 10.5- to 18.5-d incubation period were used to calculate eggshell water vapor conductance (G(H2O)), specific G(H2O) (g(H2O); G(H2O) adjusted to 100 g of set egg weight basis), and a G(H2O) constant (K(H2O)) for each egg. Chicks were grown out for 10 d in pens of a single battery brooder. In each pen, on d 3 posthatch, carcasses, yolk sac, liver, and pipping muscle samples were collected from at least 2 chicks that hatched from eggs implanted with transponders for determination of their relative weights and moisture concentrations. Livers and pipping muscles were also analyzed for glucose, glycogen, fat, and protein concentrations. Yolk sac weight as a percentage of chick BW (YW) and its moisture concentration (YSM) were positively correlated with T(emb). Egg g(H2O) was positively correlated with chick carcass moisture concentration and its relative weight as a percentage of set egg weight, but it was negatively correlated with YW. The positive functional relationship between T(emb) and incubation length may be mediated via their common positive relationships to YSM. A negative correlation was observed between percentage EWL and relative BW on d 0 and 0.5 posthatch for chicks hatched from unimplanted eggs. The results suggest that a higher g(H2O) results in an increased metabolism of the broiler embryo, which subsequently increases growth and yolk sac absorption in broiler chicks through 3 d posthatch.

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.

Maximizing carbon dioxide content of shell eggs by rapid cooling treatment and its effect on shell egg quality

Rapid cooling of shell eggs using liquid CO₂ has been shown to cool eggs to 7°C within minutes, as opposed to days required by traditional cooling treatments. This quick-cooling technique is component in the maintenance of egg quality and extended shelf life beyond the current 30- to 45-d period. The hypothesis for the current study was that maximizing CO₂ content of the eggs during cooling may increase Haugh units and thus extend shelf life (physical quality factors). The objective of this study was to maximize CO₂ content of shell eggs during rapid cooling with liquid CO₂ and determine its effect on egg quality during 12 wk of refrigerated storage. Three cooling conditions selected for the study were -45°C for 18 min (treatment A), -60°C for 15 min (treatment B), and -75°C for 12 min (treatment C). After rapid-cooling treatment, it took approximately 25 min for the internal temperature of eggs to equilibrate to 7°C. The Haugh units of the rapidly cooled eggs were significantly higher than the traditionally cooled (control) eggs. After 12 wk of refrigerated (5-7°C) storage, control eggs were only 37% AA-grade, 57% A-grade, and 6% B-grade. In comparison, all the rapidly cooled eggs averaged to 80% AA-grade and 20% A-grade. After 6 wk, the average quality of control eggs reduced to grade A, whereas rapid cooling treatment was able to maintain AA quality up to 12 wk. The CO₂ content of the rapidly cooled eggs (1.8 mg of CO₂/g of albumen) showed no difference between treatments A, B, and C, but it was significantly higher than the control (1.3 mg of CO₂/g of albumen). In addition, the vitelline membrane strength of the control decreased 65% during storage and was between 30 and 50% of the vitelline membrane strength of CO₂-cooled eggs at 12 wk. Rapid cooling with liquid CO₂ extends shelf life of shell eggs.

Dual function of egg-covering in the Kentish plover Charadrius alexandrinus

Many bird species take recesses during incubation, and while the nests are unattended, the eggs may both be vulnerable to predation and reach suboptimal temperatures for embryo development. Perhaps to avoid these negative possibilities, some birds cover their eggs with materials when they depart from nests. We examined experimentally, using the ground-nesting Kentish plover as model species, whether egg-covering allows egg temperatures to remain within optimal limits for embryogenesis in unattended nests, thus reducing the requirements of contact incubation, and simultaneously maintain the eggs’ camouflage. There was a negative relationship between nest attendance and ambient temperature, but only during mid-morning, the period of the day when eggcovering was most frequent. Indeed, during mid-morning egg-covering not only served to better camouflage the eggs, but also to maintain egg temperatures within optimal thermal thresholds for embryogenesis while the nests remained unattended. During other periods of the day, covered eggs in unattended nests overheated (e.g., afternoon) or did not reach the optimal temperature for embryogenesis (e.g., early morning). During periods in which eggs may be uncovered to alleviate overheating, unattended nests may be easier to locate by predators, because the eggs are less well camouflaged. Therefore, camouflage and appropriate thermal environment are inseparable functions of egg-covering in the ground-nesting Kentish plover.

호박꽃과실파리 온도 발육모형

The striped fruit fly, Bactrocera scutellata, damages pumpkin and other cucurbitaceous plants. The developmental period of each stage was measured at seven constant temperatures (15, 18, 21, 24, 27, 30, and ). The developmental time of eggs ranged from 4.2 days at to 0.9 days at . The developmental period of larvae was 4.2 days at , and slowed in temperatures above . The developmental period of pupa was 21.5 days at and 7.6 days at . The mortality of eggs was 17.1% at and 22.9% at , Larval mortalities (1st, 2nd, 3rd) were 24.1, 27.3 and 18.2%, respectively, at , Pupal mortalities were 18.2% at and 23.1% at . The relationship between developmental rate and temperature fit both a linear model and a nonlinear model. The lower threshold temperatures of eggs, larvae, and pupae were 12.5, 10.7, and , respectively, and threshold temperature of the total immature period was . The thermal constants required to complete the egg, larval, and pupal stages were 33.2, 118.3, and 181.2 DD, respectively. The distribution of each development stages was described by a 3-parameter Weibull function.

Retail food safety risks for populations of different races, ethnicities, and income levels.

Research has found that populations with low socioeconomic status (SES) and minority populations have greater access to small corner markets and less access to supermarkets than high-SES and Caucasian populations. This represents a significant difference in the farm-to-fork continuum that these populations experience. This research examined whether differential retail access to foods results in different food safety risks at the retail level for consumers with different demographics. U.S. Census Bureau census tracts with high African American, Asian, Hispanic, Caucasian, low-SES, and high-SES populations were identified in Philadelphia, PA. Approximately 60 retail food establishments were sampled in each census tract category from June 2008 to June 2010. Food samples collected at stores included milk, eggs, lunchmeat, sandwiches, and ready-to-eat (RTE) fresh fruit, greens, and herbs, when available. With the exception of milk and eggs, only food that had been handled and/or prepared at the retail level was sampled. Food samples were tested for temperature, aerobic plate count, coliforms, fecal coliforms, Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes. The results indicated that internal egg temperatures were higher in samples from low-SES census tracts than in eggs from Caucasian census tracts, and eggs were more often found unrefrigerated in markets in low-SES and Asian census tracts. Milk samples from markets in Hispanic and low-SES census tracts had higher aerobic plate counts than high-SES census tract samples. Sandwiches from markets in high-SES census tracts had higher coliform counts than sandwiches from markets in all other census tract categories. Markets in Asian census tracts had a higher incidence of fecal coliform contamination on sandwiches than markets in Caucasian census tracts. Fecal coliforms were present in a percentage of RTE greens from markets in all census tracts except African American, with the highest percentages of RTE greens positive for fecal coliforms in low-SES (100%), Asian (71.4%), and Caucasian (45.5%) markets.

Effects of in ovo injection of carbohydrates on embryonic metabolism, hatchability, and subsequent somatic characteristics of broiler hatchlings

The effects of the in ovo injection of different carbohydrate solutions on the internal egg temperature (IT), hatchability, and time of hatch of embryonated Ross × Ross 708 broiler hatching eggs were determined. In addition, the BW, liver weight, yolk sac weight (YSW), and yolk-free BW (YFBW) of the embryos on d 19.5 of incubation and of the chicks on day of hatch were determined. Eggs containing live embryos were injected in the amnion on d 18.5 of incubation using an automated multiple-egg injector. Solution injections delivered 1.2 mL of physiological saline (0.85%) alone or with a supplemental carbohydrate. The following supplemental carbohydrates were separately dissolved in saline at a concentration of 0.3 g/mL: glucose, fructose, sucrose, maltose, and dextrin. Temperature transponders were implanted in the air cells of embryonated and nonembryonated eggs after in ovo injection for the detection of IT at 6, 14, and 22 h after injection. The IT of embryonated eggs was significantly greater than that of nonembryonated eggs at all 3 times after the treatment period. Eggs that were injected with saline with or without supplemental carbohydrates experienced a reduction in IT when compared with control eggs whose shells were perforated without solution delivery, and the decrease in IT was associated with a delay in hatch time. Liver weight was negatively related to YSW and positively related to YFBW, and YSW was negatively related to YFBW. Although the saline and carbohydrate solution injections increased chick BW compared with noninjected controls, chick YFBW was decreased in the maltose- and sucrose-injected groups. In conclusion, the injection of 1.2 mL of saline with or without supplemental carbohydrates lowered embryonic metabolism, as reflected by a lower IT and a delay in time of hatch. However, effects of the different carbohydrate solutions on yolk absorption and tissue deposition in yolk-free embryos varied. These results suggest that lower volumes for solutions containing maltose, sucrose, or fructose should be considered for in ovo injection.

A 3-D computational fluid dynamics model for forced air cooling of eggs placed in trays

Freshly laid shell eggs must be cooled quickly for controlling Salmonella Enteritidis (SE) growth. To fulfill a research need identified by Food Safety and Inspection Service (FSIS), a 3-D computational fluid dynamics (CFD) model was developed to predict the temperature of eggs placed on a tray (6 rows×5 columns) under forced air cooling. The continuity, momentum, and energy equations were solved along with standard k−ε turbulence model using PHOENICS software. The model was validated by conducting experiments in a wind tunnel at various air temperatures (7–11°C) and velocities (0.3–0.7m/s). Root mean square error for predicting yolk temperatures was within 1°C. Finally, the CFD model was integrated with a microbial growth model to estimate the risk of SE growth during cooling. This model can be incorporated into the FSIS risk assessment model for more accurate estimation of SE risk in shell eggs.

Partial Incubation in Birds: Its Occurrence, Function, and Quantification

Early studies of incubation behavior acknowledged the existence of a less regular form of incubation that can occur from the beginning of egg laying to shortly after clutch completion. It has been variously termed “partial incubation” (Putnam , Seel , Ashkenazie and Safriel ), “brooding” (Barth ), “intermittent incubation” (Samuel ), “irregular incubation” (Beer ), or “nonrhythmic incubation” (Morton et al. ). This form of incubation has been described from visual observations of adults sitting on the nest less regularly, and from egg temperatures that are lower and more variable than those typically attained after clutch completion (Barth , Brackbill , Kendeigh , Barrett , Morton and Pereyra ). We refer to this little-understood behavior as “partial incubation” because it is characterized by a reduced amount of time during egg laying that parents sit on and warm their eggs, compared with the amount and intensity of incubation they provide later in the nesting cycle after the clutch is complete. Partial incubation is a common way for birds to initiate incubation. The onset of incubation, the moment at which a bird begins to incubate a clutch, is a critical event in the avian nesting cycle because it has important effects on fitness, as noted more than half a century ago by David Lack (). Incubation onset can affect hatching success and hatching patterns (Nilsson and Svensson , Wang and Beissinger ), nestling growth and development (Slagsvold et al. , Bitton et al. ), fledging success (Hebert , Hebert and McNeil ), and postfledging survival and recruitment (Cam et al. ). Not only can the onset of incubation affect adult reproductive rates, but it also influences and is influenced by parental body condition and survival (Hanssen et al. ). Yet the onset of incubation is rarely described and even less commonly quantified, and methods of determining incubation onset have not been standardized among studies or species. In this review, we () clarify terminology for the onset of incubation, refine the concept of partial incubation, and summarize the prevalence of partial incubation. We then () examine the potential functions of partial incubation, () map individual-level patterns of partial incubation from previous studies onto a recently developed typology of patterns for the onset of incubation (Wang and Beissinger ), and examine intraspecific variability and compare interspecific data with respect to taxonomic and ecological diversity. We also () provide a standardized method for determining the individual onset of full incubation, using complete records of nest attendance or incubation from the start of laying to beyond clutch completion. Our goal is to show how data from disparate studies can be used to test hypotheses about the function of partial incubation. Finally, we () offer questions that may prove to be fertile areas of research and suggest ways to standardize future data collection and analysis to benefit common research goals. TERMINOLOGY FOR THE ONSET OF INCUBATION