Hatching Period Research Articles

Incorporating Organophosphate Alternative Insecticides Into Codling Moth Management Programs in Washington Apple Orchards

Azinphos-methyl (AZM) has been the most used insecticide in apple production in the United States since the late 1960s, primarily as a control for the key pest of apple ( Malus domestica Borkh.), codling moth ( Cydia pomonella L.). A decision by the EPA to phase out AZM by 2012 signals the end of this product's use by tree fruit growers. In recent years, many new insecticides have been registered to replace AZM. These new insecticides have unique modes of action, but growers will need to change their traditional management practices to achieve the level of control they were accustomed to with AZM. Field trials were conducted from 2004 to 2008 to explore new application timings and strategies that incorporated insecticides with different modes of action and targeted life stages. It was apparent that new insecticides could not provide fruit protection superior to protection provided with AZM. However, strategies were developed that in many cases allowed equivalent control to the level of control experienced with a codling moth program based on AZM. The most successful strategies employed insecticides that targeted both eggs (ovicides) and larvae (larvicides). An insect growth regulator (ovicide) applied at the start of the oviposition period followed by two larvicide applications that targeted the peak egg hatch period provided fruit protection equivalent to the protection given by AZM applied twice.

Evaluation of a clutch‐containment method during hatch in geese: Using resident Canada geese as an example

AbstractDisruption associated with nest visits during the hatch period of waterfowl can cause partial abandonment of hatchlings, potentially causing bias in the survival of marked birds. We evaluated the use of a mesh clutch‐containment bag to capture and mark entire broods of 151 resident Canada goose (Branta canadensis) nests, prior to hatch, while minimizing observer‐caused disruption during brooding. The study was conducted in New Jersey, USA, from April to June 2010. No differences were found in hatch success or the number of hatchlings marked between contained clutches and the control group. Although this technique was not beneficial in studying gosling survival in temperate nesting populations, it may be effective in sub‐Arctic nesting conditions where nest visits are conducted using a more invasive approach such as a helicopter. © 2012 The Wildlife Society.

Environmentally Cued Hatching in Reptiles

Evidence is accumulating for the widespread occurrence of environmentally cued hatching (ECH) in animals, but its diversity and distribution across taxa are unknown. Herein I review three types of ECH in reptiles: early hatching, delayed hatching, and synchronous hatching. ECH is currently known from 43 species, including turtles, crocodilians, lizards, snakes, tuatara, and possibly worm lizards. Early hatching caused by physical disturbance (e.g., vibrations) is the most commonly reported ECH across all groups; although it apparently serves an antipredator function in some species, its adaptive value is unknown in most. Delayed hatching, characterized by metabolic depression or embryonic aestivation, and sometimes followed by a hypoxic cue (flooding), occurs in some turtles and possibly in monitor lizards and crocodilians; in some of these species delayed hatching serves to defer hatching from the dry season until the more favorable conditions of the wet season. Synchronous hatching, whereby sibling eggs hatch synchronously despite vertical thermal gradients in the nest, occurs in some turtles and crocodilians. Although vibrations and vocalizations in hatching-competent embryos can stimulate synchronous hatching, cues promoting developmentally less advanced embryos to catch up with more advanced embryos have not been confirmed. Synchronous hatching may serve to dilute predation risk by promoting synchronous emergence or reduce the period in which smells associated with hatching can attract predators to unhatched eggs. Within species, advancing our understanding of ECH requires three types of studies: (1) experiments identifying hatching cues and the plastic hatching period, (2) experiments disentangling hypotheses about multiple hatching cues, and (3) investigations into the environmental context in which ECH might evolve in different species (major predators or abiotic influences on the egg, embryo, and hatchling). Among species and groups, surveys for ECH are required to understand its evolutionary history in reptiles. The probability of ECH occurring is likely influenced by a species's life history, ecology, behavior, and interrelationships with other species (e.g., sizes of predator and prey). More broadly, the discovery of embryo-embryo communication as a mechanism for synchronous hatching in crocodilians and turtles indicates that the social behavior of (nonavian) reptiles has been underestimated.

Canola, corn, and vegetable oils as alternatives for wheat germ oil in fruit fly larval diets

Four wheat germ oil alternatives (corn oil, vegetable oil, canola oil with 10% vitamin E, and canola oil with 20% vitamin E), purchased from a local supermarket in Hawaii, were added to a fruit fly liquid larval diet as a replacement for wheat germ oil in the rearing of fruit fly larvae. The oils were tested on three species of fruit flies in Hawaii, Ceratitis capitata (TSL strain), Bactrocera dorsalis, and Bactrocera cucurbitae. They were evaluated for their efficacy in replacing WGO, based on: pupal recovery (%), larval duration (d), pupal weight (mg), adult emergence (%), adult fliers (%), mating (%), egg production per female per day, egg hatch (%), and peak egging period (d). Diets with WGO and without any oil were used as controls. The objective of the study was to select the most cost effective alternative oils with the best performance to replace the currently used WGO, which is pricey and hard to find. The results showed that there was no significant difference in performance among the tested oils in B. cucurbitae and B. dorsalis as regards the above mentioned parameters. Lower mating rate was observed in B. cucurbitae from those reared in vegetable oil and canola oil (10% vitamin E) diet. Lower egg production and egg hatch were obtained with B. dorsalis whose larvae were reared in vegetable and canola oil (both 10% and 20% vitamin E). Vegetable oil diet seemed to reduce pupal weight, shorten larval duration, and increase pupal recovery of C. capitata. The results suggest that WGO can be substituted with corn oil, vegetable oil, or canola oils for B. cucurbitae, while corn oil is a better alternative for B. dorsalis, and vegetable oil is best for C. capitata.

Ontogeny of the Shell Bones of Embryos of Podocnemis unifilis (Troschel, 1848) (Testudines, Podocnemididae)

The aim of the present study was to investigate the sequence of shell bone formation in the embryos of the Pleurodira, Podocnemis unifilis. Their bones and cartilage were collected and cleared before staining. The shell was also examined by obtaining a series of histological slices. All the bony elements of the plastron have independent ossification centers, which subsequently join together and retain two fontanelles until the period of hatching. This turtle has a mesoplastra, which is characteristic of the Podocnemididae. The carapace begins to form concurrently with the ossification of the ribs at the beginning of stage 20. All the plates, except the suprapygal, initiate ossification during the embryonic period. The main purpose of the histological investigation was to highlight the relationship between the formation of the carapace and ribs with that of the neural plates. The costal and neural plates were found not to independent ossification centers, but to be closely related to components of the endoskeleton, originating as expansions of the perichondral collar of the ribs and the neural arches, respectively. Considering the ribs as an endoskeletal element of the carapace, the carapace and plastron begin ossification at the same stage in P. unifilis. This pattern reveals similarities with other Pleurodira, as well as evident variations, such as the presence of the seven neural bones and the presence of only one ossification center in the nuchal plate.

Genetic Variability of Hatchability Estimated Based on Multiple-trait Model

Rozempolska-Rucinska, I., Zieba, G., Lukaszewicz, M. and Ciechonska, M. 2010. Genetic variability of hatchability estimated based on multiple-trait model. J. Appl. Anim. Res., 38: 175–180. To verify whether hatchability rates in successive hatches of egg-laying chickens may be regarded as separate traits, 8 generations of layers from a maternal Rhode Island White (≈4200 hens) and paternal Rhode Island Red (≈2600 hens) lines were involved. (Co)variance components were estimated by means of the REML method using the multiple-trait animal model. The birds' breeding merit was assessed with the BLUP method. There was no ground for regarding the successive hatches as separate traits. The number of chicks hatched in consecutive hatches is a measure of the same trait assessed in various periods. High genetic correlations between the particular hatching periods facilitate assessment of birds' breeding merit on the basis of the first hatch results. Thus, it would be possible to verify the breeding stock rank and to select family flocks for subsequent reproduction of the offspring.

Artificial light at night: implications for early life stages development in four temperate freshwater fish species

Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction. To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination (LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments. In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub. Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching. The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach. In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has not been identified on early life stages.

Relationship of early laying, number and weight of laid eggs to fertility and hatchability of eggs in initial laying lines of hens

Abstract. The relationships between age of hens, number of laid eggs, egg weight on one hand and fertility and hatchability on the other were analysed during two periods of individual pedigree hatching. Altogether 1 369 hens originated from 9 selected initial laying lines of Bar Plymouth Rock (BPR) (3 lines), Rhode Island Red (RIR) (4 lines), Rhode Island White (RIW), and Sussex Light (SUL) breeds. A total number of 23 473 eggs from hens of all 9 aforementioned lines were set after being artificially inseminated. The total average hatchability of set eggs was 73.2 % and the average percentage of unfertilised eggs was 9.3 %. Positive correlations (rp =0.22 to rp =0.72; P<0.01) were found between the total number of eggs laid till the 240th day of age and the number of eggs produced at the beginning of the laying period in the all studied lines. There were negative correlations (rp =−0.03 to rp =−0.16; P<0.01) between the total number of eggs laid till the 240th day of age and the average egg weight (on the 222nd day of age). Zero to positive correlations existed between the total number of eggs laid till the 240th day of age on one hand and the number of hatching eggs, number of hatched chicks/hen and hatchability; the calculated values ranged from rp =−0.02 to rp =0.30 (P<0.01), from rp = −0.08 to rp =0.36 (P<0.01), and from rp =−0.09 to rp =0.30 (P<0.01), respectively. Correlations between the egg weight and number of hatched chicks/hen were negative to zero and their values ranged from rp =−0.19 (P<0.01) to rp =0.02. Correlations between the egg weight and hatchability were always negative (rp =−0.15; P<0.05 to rp =−0.04). Regarding the fact that there is a concurrent selection for an increased egg weight it can be said that this preference of smaller eggs is really counter-productive. A positive relationship between the number of hatching eggs/hen and the hatchability (rp =−0.02 to rp =0.39; P<0.01) was influenced by calculated negative correlations existing between the weight of eggs and the hatchability as well as between the weight of eggs and the number of laid eggs. As far as the hatchability is concerned, it can be concluded that in the aforementioned laying lines those hens are preferred, which produce more eggs of smaller size and that this fact obviously influences also the efficiency of selection for a greater weight of produced eggs.

Synchronisation of egg hatching of brown hairstreak (Thecla betulae) and budburst of blackthorn (Prunus spinosa) in a warmer future

Synchronisation of the phenology of insect herbivores and their larval food plant is essential for the herbivores’ fitness. The monophagous brown hairstreak (Thecla betulae) lays its eggs during summer, hibernates as an egg, and hatches in April or May in the Netherlands. Its main larval food plant blackthorn (Prunus spinosa) flowers in early spring, just before the leaves appear. As soon as the Blackthorn opens its buds, and this varies with spring temperatures, food becomes available for the brown hairstreak. However, the suitability of the leaves as food for the young caterpillars is expected to decrease rapidly. Therefore, the timing of egg hatch is an important factor for larval growth. This study evaluates food availability for brown hairstreak at different temperatures. Egg hatch and budburst were monitored from 2004 to 2008 at different sites in the Netherlands. Results showed ample food availability at all monitored temperatures and sites but the degree of synchrony varied strongly with spring temperatures. To further study the effect of temperature on synchronisation, an experiment using normal temperatures of a reference year (T) and temperatures of T + 5°C was carried out in climate chambers. At T + 5°C, both budburst and egg hatch took place about 20 days earlier and thus, on average, elevated temperature did not affect synchrony. However, the total period of budburst was 11 days longer, whereas the period of egg hatching was 3 days shorter. The implications for larval growth by the brown hairstreak under a warmer climate are considered.

Timing of fledging is influenced by glucocorticoid physiology in Laysan Albatross chicks

Fledging is a major life transition for birds, when juveniles move from the safety of a nest into an environment where they must find food and avoid predators. The timing of fledging within a season can have significant effects on future survival and breeding success. Proximate triggers of fledging are unknown: though wing development is likely a primary factor, other physiological changes, such as elevated plasma corticosterone (CORT), may affect fledging behavior. Laysan Albatross ( Phoebastria immutabilis) chicks have an extended post−hatching period during which they reach 150% of adult mass. However, approaching fledging, chicks fast for days to weeks and lose mass while still putting energy into feather growth. We evaluated chick morphology and physiology to elucidate proximate triggers of fledging. As in some other species, CORT increased as chicks fasted and lost body mass. At the same time, corticosteroid binding globulin (CBG) declined, thus amplifying free CORT prior to fledging. Once chicks reached a morphological threshold, free CORT levels predicted how long they stayed at the colony: chicks with higher free CORT fledged sooner. To perturb the relationship between body condition, endocrine physiology, and fledging behavior, we supplementally fed chicks for the month before fledging. Fed birds had a slower decrease in body mass, slower decrease in CBG, slower increase in free CORT, and stayed at the colony longer after reaching a morphological threshold. Our study suggests that as chicks lose mass, free CORT acts as a signal of energetic or nutritional state to adjust the timing of fledging.

The life cycle and biological characteristics of Dermacentor silvarum Olenev (Acari: Ixodidae) under field conditions

In this study, we investigated the life cycle and biological characteristics of all developmental stages of Dermacentor silvarum under field conditions in Hebei province in North China. Larvae, nymphs and adults were fed on rabbits, and maintained under natural lighting and climate conditions. Ticks were released into a confined plot located in natural tick habitat, and we observed the host questing behavior and seasonal occurrence. Due to a behavioral diapause in females and the synchronization of oviposition and larval hatching, D. silvarum only active from late February to early September under field conditions. The duration of the life cycle of D. silvarum was highly variable due to different preovipositional and egg hatching periods for ticks engorging in March, April or May. The developmental periods of larvae (18 days) and nymphs (29 days) under field conditions were similar to those under laboratory conditions. Moreover, there was a highly significant correlation between engorged body weight of females and egg masses laid ( r = 0.76, p < 0.001). The female reproductive efficiency index (REI) in March, April and May was 5.7, 7.1 and 6.2, respectively. Finally, we also observed different ovipositional patterns between females that engorged in the field and those that engorged under laboratory conditions.

The life history of Perla bipunctata Pictet, 1833 (Plecoptera: Perlidae) in the upper River Liffey, Ireland

Perla bipunctata is the most common species of Perlidae in Ireland occurring in fast flowing, clean rivers and small streams. Although a common component of freshwater biological studies, little is known about the autecology of this stonefly. Monthly kick and Surber samples were taken over a 1-year period in the upper reaches of the River Liffey (4th order) to determine the life history of larvae. Perla bipunctata has a merovoltine life cycle taking no less than three years to complete the immature stages. Life history plots suggest two periods of egg hatching, followed by two separate cohorts developing over different lengths of time. Mature larvae from both cohorts synchronise and emerge as adults over a short period in early summer. The merovoltine life cycles of long lived invertebrates like P. bipunctata emphasise the importance of such species in reflecting the ecological quality of freshwaters over a long period of time.

Chicken folliculo-stellate cells express thyrotropin receptor mRNA

We investigated the presence of thyrotropin receptor (TSHR) mRNA in chicken pituitary and brain, and quantified the changes in its expression during the last week of embryonic development. We found that in the pituitary gland, TSHR mRNA co-localizes with folliculo-stellate cells but not with thyrotropic cells, suggesting the existence of a paracrine ultra-short thyrotropin feedback loop. TSHR mRNA was also present throughout the diencephalon and various other brain regions, which implies a more general function for thyrotropin in the avian brain. During late embryogenesis, when the activity of the hypothalamo-pituitary-thyroidal axis increases markedly, a significant rise in TSHR mRNA expression was observed in pituitary, which may signify an important change in pituitary ultra-short thyrotropin feedback regulation around the period of hatching.

Ação do fungo Beauveria bassiana associado a gel polimerizado de celulose no controle do carrapato Anocentor nitens em teste de campo

Foram selecionados 20 equídeos naturalmente infestados por Anocentor nitens, dos quais seus pavilhões auriculares foram submetidos a quatro tratamentos distintos: gel associado a Beauveria bassiana, apenas gel, apenas B. bassiana e um grupo-controle. Procederam-se à contagem e ao registro do número total de fêmeas adultas (&gt;3mm) em cada pavilhão auricular, nos dias 0, 1, 4, 7, 11, 14, 18, 21, 25 e 28, para cálculo do percentual de controle. Foram coletadas e mantidas em laboratório 20 fêmeas pertencentes a cada tratamento, para cálculo dos períodos de pré-postura, postura, incubação e eclosão, e peso médio das posturas. No grupo tratado com o composto gel associado a B. bassiana, observou-se percentual de controle maior que 50%, entre o 4º e o 25º dia, assim como decréscimo progressivo do peso médio da postura das fêmeas coletadas no período entre o 7º e 14º dia. Para os outros tratamentos, o percentual de controle manteve-se abaixo de 20%, e o peso da postura não apresentou diferença significativa. Os percentuais de controle, assim como as reduções no peso médio da postura, sugerem que a utilização do composto gel associado a B. bassiana potencializou a virulência do entomopatógeno.

Age-Dependent Postdiapause Development in the Gypsy Moth (Lepidoptera: Lymantriidae) Life Stage Model

For the last approximately 10 yr, the Gypsy Moth Life Stage (GLS) model has been used by pest managers to predict when important events in the gypsy moth, Lymantria dispar L., life cycle will occur (e.g., peak second larval instar population and male moth flight). Although the GLS model has been shown to outperform other gypsy moth phenology models, its predictions have not always been as accurate as desired. Differences between predicted and observed egg hatch phenology prompted a re-examination of the original experimental data that were used in the construction of the egg hatch submodels of the original GLS model, and a data processing error was discovered to have truncated the postdiapause experimental data. Analysis of the complete data set confirmed that developmental rates in the postdiapause phase were age and temperature dependent but that the developmental response to temperature is distinctly nonlinear at postdiapause initiation, in contrast to the indeterminate response previously reported. By incorporating the new estimates of developmental rate patterns and parameters into the GLS model, errors in the GLS-simulated egg hatch period were reduced by 33-71% and error in date of 50% cumulative egg hatch by 25-100%.

Ultrastructural features and elemental distribution in eggshell during pre and post hatching periods in the green turtle, Chelonia mydas at Ras Al-Hadd, Oman

Eggshells were randomly collected from turtle nests immediately after oviposition and at the end of incubation to examine the ultrastructural features using scanning JSM-5600LV microscopy. Three layers were recognized; an outer calcareous, a middle multistrata and an inner membrane. The calcareous layer had loose nodular units varying in shape and size without interlocking attachments. In freshly laid eggs, each nodular unit had spicules arranged in folded stacks. The spicules became unfolded during incubation, to form radiating configurations. Elemental composition and mapping of the layers were analyzed using energy dispersive spectroscopy (EDS). The elements were unevenly distributed throughout the eggshell and Ca 2+ decreased significantly after hatching. X-ray diffraction was used to identify the crystals of the eggshells. It revealed that nodular units of the calcareous were made up of CaCO 3, as aragonite (91%), calcite (6%) and vaterite (3%). The middle layer consisted of organic amorphous material with aragonite (89%) and calcite (11%). The shell membrane consisted of reticular fibers with crystals predominantly of NaCl halite. Thermogravimetry analysis of the calcareous layer indicated a complete evaporation of bonded H 2O at 480 °C and CO 2 at 830 °C. Using the differential thermal analysis (DTA), aragonite was transformed to stable calcite at 425 °C.

Effect of temperature on early life history in weatherfish,Misgurnus fossilis(L. 1758)

Effect of incubation temperature (range: 9–36 °C; interval: 3 °C) on artificially propagated weatherfish (Misgurnus fossilis ) early ontogeny (during interval from egg fertilization to the finish of hatching) was investigated. Both, the amplitude of the incubation period (evaluated in four crucial moments), the total hatching period duration was inversely proportional to the incubation temperature and ranged from 17.5 days at 9 °C to 1.8 days at 24 °C (expressed at H50 ) or from 137 hours at 9 °C to 9 hours at 24 °C, respectively. There were no influence of rising temperature on the total length of newly hatched larvae (TL = 4.23–4.67 mm), in contrast to negative correlation with developmental stage (9–18 °C: stage 37; 21–24 °C: stage 36), i.e. the length might determine the age at hatching, rather than the age at hatching determines the hatching length. The thermal tolerance range in term of survival lies between 9 and 24 °C (the thermal optimum 15–24 °C, i.e. weatherfish is a warm-mesothermic species). Temperatures above 24 °C (in our study 27–36 °C) are considered the lethal temperatures already during embryonic period. It is highly recommended to distinguish an impact of suboptimal temperatures 9–12 °C on development during explored interval only, in contrast to possible other effect of these lower temperatures in context of the whole early ontogeny.

Emergence of larval yellow perch, Perca flavescens, in South Dakota lakes: potential implications for recruitment

Abstract Temporal patterns in length frequency distributions and hatch dates were described for larval yellow perch, Perca flavescens (Mitchill), captured in surface ichthyoplankton trawls from late April to mid‐June 2000 to 2002 in six South Dakota, USA lakes. Fewer than 15 larval yellow perch were collected in four of six lakes during 2002, suggesting that in some cases factors prior to, during or immediately after hatching likely play a critical role in the perch recruitment process. When larval yellow perch were encountered in larger numbers, temporal trends in total length (TL) frequencies indicated that only a single cohort was produced annually in each lake. Most yellow perch in these lakes hatched between 29 April and 17 May, and most hatching occurred during 5–11 days each year. Larval TL was not related to hatch date. The apparent prevalence of relatively short hatch periods in these yellow perch populations probably increases the risk of catastrophic losses resulting from periods of poor environmental conditions.

Sandeel (Ammodytes marinus) larval transport patterns in the North Sea from an individual-based hydrodynamic egg and larval model

We have calculated a time series of larval transport indices for the central and southern North Sea covering 1970–2004, using a combined three-dimensional hydrodynamic and individual-based modelling framework for studying sandeel ( Ammodytes marinus ) eggs, larval transport, and growth. The egg phase is modelled by a stochastic, nonlinear degree-day model describing the extended hatch period. The larval growth model is parameterized by individually back-tracking the local physical environment of larval survivors from their catch location and catch time. Using a detailed map of sandeel habitats in the North Sea, the importance of hydrography for early life stages of sandeel to their recruitment success is explored. We find that the sandeel larval transport patterns in the North Sea are relatively robust toward uncertainties in biological parameters, when mortality aspects are included. We find only weak spatiotemporal correlations between elements of the transport indices in the time series, mainly positive correlation between retention terms for the same year. The transport connectivity of sandeel habitats in the North Sea and the dynamical properties of the North Sea transport system are also analyzed, and we introduce novel a scheme to quantify direct and indirect connectivity on equal footings in terms of an interbank transit time scale.

Effect of the dusk photoperiod change from light to dark on the incubation period of eggs of the spotted rose snapper, Lutjanus guttatus (Steindachner)

Spotted rose snapper, Lutjanus guttatus (Steindachner), eggs were incubated under different photoperiods to examine the effect of photoperiod on incubation. The eggs from two fish were incubated under five artificial photoperiods: constant dark (D), constant light (L) from 06:00 hours and 6, 10 and 14 h of light from 06:00 hours. The eggs from seven other fish were incubated under a natural photoperiod. Different spawning times (21:00 – 01:00 hours) and different photoperiods combined to give the start of the dusk photoperiod change after 11–23 h of incubation. Constant light or applying the dusk photoperiod change after ≥20 h of incubation appeared to extend the hatching period. The mean hatching period for groups of eggs incubated in darkness or that received the dusk photoperiod change after ≤19 h of incubation (n=8 different groups) was 2 h 15±10 min, which was significantly lower (P<0.05) than the mean hatching period of 4 h±37 min for groups that did not receive the dusk photoperiod change or that received the dusk photoperiod change after ≥20 h of incubation (n=9 groups). However, despite these differences, the majority of the eggs hatched during a 2–3 h period from 17 to 20 h of incubation, and a sigmoid regression (r2=0.9) explained the relationship between percentage hatch and hours of incubation for all photoperiod groups.