Inter-nesting Interval Research Articles

Effect of water temperature on the duration of the internesting interval across sea turtle species

Sea turtles generally lay several clutches of eggs in a single nesting season. While a negative correlation between water temperatures and the time required between constitutive nesting events (termed the internesting interval) has been previously reported in loggerhead Caretta caretta and green turtles Chelonia mydas, it is not understood whether this relationship remains constant across other sea turtle species. Here, we expanded upon these previous studies on loggerhead and green turtles by using larger sample sizes and including data from species with a wider range of body-sizes; specifically: hawksbill Eretmochelys imbricata, leatherback Dermochelys coriacea, and olive ridley turtles Lepidochelys olivacea. In total, we compiled temperature data from biologgers deployed over internesting intervals on 23 loggerhead, 22 green, 7 hawksbill, 26 leatherback and 11 olive ridley turtles from nesting sites in 8 different countries. The relationship between the duration of the internesting interval and water temperatures in green and loggerhead turtles were statistically similar yet it differed between all other turtle species. Specifically, hawksbill turtles had much longer internesting intervals than green or loggerhead turtles even after controlling for temperature. In addition, both olive ridley and leatherback turtles exhibited thermal independence of internesting intervals presumably due to the large body-size of leatherback turtles and the unique capacity of ridley turtles to delay oviposition. The observed interspecific differences in the relationship between the length of the internesting interval and water temperatures indicate the complex and variable responses that each sea turtle species may exhibit due to environmental fluctuations and climate change.

Breeding site attendance and breeding success in Phyllomedusa trinitatis (Anura: Phyllomedusidae)

Using a natural marker, we documented breeding site attendance patterns by males and females of the Trinidad Leaf Frog, Phyllomedusa trinitatis. We followed attendance at a cluster of three isolated ponds over 53 and 56 consecutive nights in 2016 and 2019 respectively. Most females attended only once, but for those that attended more than once we calculated an inter-nesting interval (mean 27.6 days, N = 7). Males showed high pond fidelity, but some did attend at two of the ponds, always with a strong preference for one of them. Males showed three attendance patterns. A few attended on multiple consecutive nights (maximum, 19 nights); more were sporadic (one attended seven times over 46 nights with gaps of 15 and 19 days in the sequence); some attended only once (2016: 12, 2019: 15), but most were found to be present on multiple nights (2016: 38, 2019: 32). Our analysis suggested that these latter frogs were either newly recruited individuals or had been predated during the study. Our data show that rainfall has some influence on attendance. We found no relationship between male body condition and attendance pattern. In addition, there was no evidence that a particular male attendance pattern was optimal for breeding success.

Activity of loggerhead turtles during the U-shaped dive: insights using angular velocity metrics

Understanding the behavioural ecology of endangered taxa can inform conservation strategies. The activity budgets of the loggerhead turtle Caretta caretta are still poorly understood because many tracking methods show only horizontal displacement and ignore dives and associated behaviours. However, time-depth recorders have enabled researchers to identify flat, U-shaped dives (or type 1a dives) and these are conventionally labelled as resting dives on the seabed because they involve no vertical displacement of the animal. Video- and acceleration-based studies have demonstrated this is not always true. Focusing on sea turtles nesting on the Cabo Verde archipelago, we describe a new metric derived from magnetometer data, absolute angular velocity, that integrates indices of angular rotation in the horizontal plane to infer activity. Using this metric, we evaluated the variation in putative resting behaviours during the bottom phase of type 1a dives for 5 individuals over 13 to 17 d at sea during a single inter-nesting interval (over 75 turtle d in total). We defined absolute resting within the bottom phase of type 1a dives as periods with no discernible acceleration or angular movement. Whilst absolute resting constituted a significant proportion of each turtle’s time budget for this 1a dive type, turtles allocated 16-38% of their bottom time to activity, with many dives being episodic, comprised of intermittent bouts of rest and rotational activity. This implies that previously considered resting behaviours are complex and need to be accounted for in energy budgets, particularly since energy budgets may impact conservation strategies.

Reproductive seasonality and environmental effects in green turtle (Chelonia mydas) nesting at Penang Island, Malaysia

AbstractFor species with environmental sex determination, understanding the relationship between reproduction and environmental factors is important for predicting their reproductive output. Here, we study intra-annual variation in green turtle nesting during the 2010–2016 seasons at Penang Island (5°16′28″–5°28′15″N 100°10′52″–100°11′55″E), Malaysia. The additive modelling on a monthly-basis number of nests shows that fluctuation in the number of nests relates to temperature in addition to month of year, rather than precipitation. The number of nests tended to be higher in response to higher temperature during March–July, whereas the lower temperature during August–February also tended to result in a relatively higher number of nests. Concentration of nests during March–July resulted from a shorter inter-nesting interval during warm temperatures, whereas relatively low temperatures may homogenize the temporal distribution of the number of nests. This study provides fundamental information for green turtle nesting seasonality in response to environmental change.

Nesting ecology of flatback sea turtles Natator depressus from Delambre Island, Western Australia

Nest site selection is likely to be important for the fitness of sea turtle populations, but data on the environmental drivers of nest site selection and other important parameters like nest site fidelity and inter-nesting and remigration intervals are limited. We address these questions using data on flipper tag resightings and track counts from flatback turtles (Natator depressus) from Delambre Island in Western Australia collected over 2–3 weeks each nesting season across six nesting seasons. The median inter-nesting interval was 13 days (range 9–17 days) and the mean±s.d. remigration interval was 1.99±0.95 years. Turtles had around 10% probability of returning to the same sector of the beach (150-m-long sections). The median distance between subsequent emergences (whether false crawls were included or not) was ~450m. The number of turtles both emerging and successfully nesting was higher when air temperature and humidity were lowest and emergences increased slightly with tide height. Sector of the beach was by far the strongest predictor of nest site, with turtles showing preference for the less exposed side of the island. The results of this study will assist with future monitoring of this population and the management of threats related to coastal development and activities.

On a Poorly Known Rookery of Green Turtles (Chelonia mydas) Nesting at the Chabahar Beach, Northeastern Gulf of Oman

There is a poorly known rookery of green turtles (Chelonia mydas) nesting in sandy beaches of Chabahar town, northeastern Gulf of Oman, Iran.This study has been carried out to evaluate nesting activity of this small rookery in 2014 nesting season (June to October). In this study, total clutches were collected and transferred to an artificial hatchery. The peak of nesting occurred from the third parts of August to the end of September. Mean CCL was 106.3 ± 6 cm and mean CCW was 94.5 ± 5 cm. Females laid on average of 99.42 ± 47.8 eggs per clutch. The mean inter-nesting interval was 18.5 days. The observed clutch frequency was 3.4. Mean hatching success was 36.63 ± 4.1%. The incubation period was 61.07 ± 5.4 days. Nest status evaluation represented that major causes for the failure was unhatched egg with no obvious embryo followed by unhatched eggs with obvious but undeveloped embryos > unhatched eggs with developed embryos > hatched eggs but dead embryos. The results achieved in this study are a valuable contribution to cognition of the reproductive ecology of the green turtle population globally and regionally.

Endangered Green Turtles (Chelonia mydas) of the Northern Mariana Islands: Nesting Ecology, Poaching, and Climate Concerns

Marine turtles in the western Pacific remain threatened by anthropogenic impacts, but the region lacks long-term biological data for assessing conservation status and trends. The Central West Pacific (CWP) population of green turtles (Chelonia mydas) was listed as Endangered by the U.S. in 2016, highlighting a need to fill existing data gaps. This study focuses on the subset of this population nesting in the Commonwealth of the Northern Mariana Islands (CNMI). Using 11 years of nesting data, we (i) estimate reproductive demographic parameters, (ii) quantify abundance and trends, and (iii) estimate the impacts of anthropogenic threats, such as poaching of nesting females and increasing sand temperatures. In 2006-2016, nesting beach surveys, identification tagging, and nest excavations were conducted on Saipan, and rapid assessments of nesting activity were conducted on Tinian and Rota. On Saipan, temperature data-loggers were deployed inside nests and evidence of poaching (adults and eggs) was recorded. This study documents year-round nesting with a peak in March–July. Nester abundance for the three islands combined was 12 ± 6 (mean ± standard deviation) females annually, with at least 63 ± 35 nests observed per year. For 39 tagged individuals, straight carapace length was 95.6 ± 4.5 cm, remigration interval was 4.6 ± 1.3 years, and somatic growth was 0.3 ± 0.2 cm yr-1. Reproductive parameter estimates included clutch frequency of 7 ± 1.3 nests per female, inter-nesting interval of 11.4 ± 0.9 days, clutch size of 93 ± 21 eggs, incubation period of 55 ± 6.4 days, hatching success of 77.9% ± 27.0, and emergence success of 69.6% ± 30.3. Mean nest temperature of 30.9 ± 1.5°C was above the pivotal threshold of 29.0°C for temperature dependent sex determination, suggesting a female-bias may already exist. Model results suggest (i) hatching success decreases and embryonic death increases when nests experience maximum temperatures beyond 34°C, and (ii) embryonic death increases in nests with mean temperatures beyond 31°C. On Saipan, 32% of nesters were poached, reducing the annual population growth rate from 11.4% to 7.4%. This study provides the first comprehensive assessment of a nesting green turtle population in the Mariana Archipelago.

Diving behavior and thermal habitats of gravid hawksbill turtles at St. Croix, USA

Knowledge of an animal’s behavior during particular life history stages can provide insights into habitat selection, and this can have important conservation implications. Gravid hawksbill turtles spend the internesting interval resting on the seafloor, but their diving behavior has only been previously examined in shallow-water habitats. We examined depth use of gravid hawksbills in a location of variable bathymetry to determine if hawksbills engage in deeper diving if deeper waters are available. We attached archival time-depth recorders onto hawksbills nesting at Sandy Point National Wildlife Refuge, St. Croix, US Virgin Islands, where the neritic zone ends within 500 m of the shoreline. We recorded seven internesting intervals from five individuals. Internesting intervals were characterized by long dives (mean 24.2 ± SD 22.3 min) to a constant depth, consistent with seafloor resting in a spatially restricted residence area. There was little variation in the water temperatures at all depths occupied (mean 29.06 ± SD 0.43 °C). Two turtles attained the deepest recorded dives for gravid hawksbills (95.1 and 84.4 m) and sometimes remained at depths greater than 60 m for up to 30 min. Although we recorded instances of relatively deep diving for the species, the overall pattern of seafloor resting and infrequent diving was consistent with hawksbills in other ocean basins with different offshore habitats. We propose that benthic resting is common behavior for gravid hawksbills globally, and protection of benthic habitats near the nesting beach should be a management priority.

Design of a protected area for inter-nesting hawksbills in Barbados: an evidence-based approach

To aid in the designation of a marine protected area for hawksbill sea turtles, Eretmochelys imbricata (Linnaeus, 1766), nesting at one of the largest rookeries in the Wider Caribbean Region (Needham's Point, Barbados), we elucidated key inter-nesting behaviors (i.e., the approximately 2-wk period of time spent at sea between nesting events) from published spatial, diving, and habitat utilization data, and the areas of overlap and potential conflict with anthropogenic uses of the coastal zone. Historically, much of the focus of conservation efforts for this species has been on protecting breeding females and their eggs from harvest, and more recently protection of nesting beaches. However, protecting the habitats in which these animals spend their inter-nesting interval and addressing the indirect anthropogenic mortality they are exposed to while in these nearshore habitats has received less attention. Despite a relatively small percentage of a hawksbill's life-cycle being spent in inter-nesting habitats, the relative value of adult females for population recovery and the vulnerability associated with large aggregations of females adjacent to rookeries makes this mature stage of their life-cycle one of high conservation priority.

Diving behaviour of hawksbill turtles during the inter-nesting interval: Strategies to conserve energy

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados were outfitted with time-depth recorders (TDRs) with temperature sensors to investigate the form and patterns of diving behaviour during the inter-nesting interval (INI; average 14.7days). All females, regardless of size, surfaced infrequently during dives of average 56min duration, and the majority of dives (90%) were spent in the bottom phase at 15–25m depths, which corresponded to the depth of benthic habitat at each location. Diving activity was highest while commuting to and from the nesting beach (about 1–2days each way), with a level of quiescence during the intermediate period (i.e. the majority of the INI). Despite little thermal variation in seawater at this latitude (13.1°N), the length of the INI was influenced by ambient sea water temperature. Diving behaviour was consistent with females conserving energy reserves built up at foraging grounds prior to arrival at the nesting beach and minimising time spent in the water column away from safe refuge at night. The frequency of surfacing and the depths at which females spend most of their time varies between sites even within one species and may be crucial in managing the risks to animals temporarily residing offshore from important nesting beaches.

Tracking hawksbill sea turtles (Eretmochelys imbricata) during inter-nesting intervals around Barbados

Hawksbill sea turtles (Eretmochelys imbricata) nesting in Barbados (Needham’s Point, 13° 04′ 41.33′′ N, 59° 36′ 32.69′′W) were outfitted with GPS dataloggers over three breeding seasons (2008–2010) to track movement during inter-nesting intervals. Most females established spatially restricted resident areas up current and within 7 km of the nesting beach where they spent the majority of the inter-nesting interval. Females nesting earlier in the season settled on shallower sites. Only experienced remigrant turtles occupied the most distant resident areas. Females tracked for multiple inter-nesting intervals exhibited site fidelity, but the area contracted and the activity of females decreased with each successive interval. Hawksbills may trade off site characteristics with distance from the nesting beach and reduce activity over the course of the breeding season to optimise energy reserves during inter-nesting intervals.

Reproductive synchrony in a recovering bottlenecked sea turtle population

1. The assessment of species extinction risk has been well established for some time now. Assessing the potential for recovery in endangered species is however much more challenging, because complementary approaches are required to detect reliable signals of positive trends. 2. This study combines genetics, demography and behavioural data at three different time-scales to assess historical and recent population changes and evidence of reproductive synchrony in a small population of olive ridley sea turtle Lepidochelys olivacea. Lepidochelys is considered as the most extraordinary example of reproductive synchrony in reptiles, yet to date, it has only been reported in large populations. 3. Using Bayesian coalescent-based models on microsatellite nuclear DNA variability, we demonstrate that effective population size in olive ridleys nesting in French Guiana has dramatically declined by 99% over the last 20 centuries. This low current population size is further illustrated by the absence of genetic mitochondrial DNA diversity in the present nesting population. Yet, monitoring of nesting sites in French Guiana suggests a possible recovery of the population over the last decade. 4. Satellite telemetry shows that over the first 14 days of their 28-days inter-nesting interval, i.e. when eggs maturation is likely to occur, gravid females disperse over the continental shelf. They then gather together with a striking spatiotemporal consistency close to the nesting site, where they later emerge for their second nesting event. 5. Our results therefore suggest that reproductive synchrony also occurs in small populations. Olive ridleys may ensure this synchrony by adjusting the duration of the second half of their inter-nesting interval prior to landing, possibly through social mediation. 6. Such reproductive synchrony may be related to the maintenance of some species-specific strategy despite former collapse and may contribute to the present population recovery. The gregarious behaviour of reproductive individuals close to shore where human-induced perturbations occur is however a cause for conservation concern for this still poorly known species.

Nesting behaviour of the Green turtle at Kosgoda rookery, Sri Lanka

Studies on nesting behaviour of turtles provide the most important information on their reproduction by providing estimates of female population size. Kosgoda, located in the southwest coast of Sri Lanka, has a year-round nesting rookery which is visited by five species of sea turtles, the green turtle being the most frequent visitor. Nesting behaviour of the female green turtle was studied at the Kosgoda rookery during a five-year period from August 2003 to July 2008. A total of 1,492 nests of the green turtle were recorded with a mean of 298.4 annual nests. Nesting took place year round, with 66 % of nesting recorded during February to June. The highest and the lowest number of nests were recorded in April and November, respectively. The average clutch size of a female green turtle was 111.5 and the clutch frequency was 2.17. The average annual nesting abundance in the study area was 138.28. Of the 2,297 nesting attempts, 805 were false crawls accounting for a nesting success of 65%. Females nesting at Kosgoda showed nest site fidelity. More than half of the females (54.3%) nested in the same beach twice or more (mean 2.17) during the same nesting season. The highest number of re-nesting recorded was ten and the mean inter-nesting interval was 13.5 days. Of the 519 individuals tagged during the study period, 56 re-visited the same beach for nesting during the subsequent nesting seasons with a mean re-migration interval of 2.56 years. One female visited the same beach three times for nesting during the study period (after 2.67 years and then after 1.83 years). The nesting behaviour of the green turtle at Kosgoda rookery was similar to those at Rekawa, the largest rookery in Sri Lanka, located in the southern coast 130 km away from Kosgoda. Rekawa beach was declared a sea turtle sanctuary in 2006. This study shows that Kosgoda beach also provides a significant nesting site for the green turtle and highlights the need to declare it as a sanctuary. Key words: clutch frequency; nesting success; re-nesting; re-migration; inter-nesting interval DOI: 10.4038/cjsbs.v39i2.2997 Cey. J. Sci. (Bio. Sci.) 39 (2): 109-120, 2010

Annual Frequency of Clutches of Pseudemys texana and Trachemys scripta at the Headwaters of the San Marcos River in Texas

I observed 215 nesting events of Pseudemys texana (134) and Trachemys scripta (81) from 25 April to 14 July 2008 on a golf course in Hays County, Texas. For P. texana, 111 (82.8%) nested one time, 21 (15.7%) nested twice, and 2 (1.5%) nested three times. For T. scripta, 53 (65.4%) nested one time, 24 (29.6%) nested twice, 3 nested three times (3.7%), and 1 nested four times (1.2%). Both species had an internesting interval of ca. 30 days between first and second clutches. Subsequent internesting intervals were shorter but samples were not sufficient to address whether this was fortuitous. On their first attempt, 82% of P. texana and 78% of T. scripta completed nesting. Nesting was diurnal with most activity occurring before noon. Neither distance to nesting site from water nor number of days from the first nesting event to the next nesting event varied with length of plastron.

Thermal and trophic habitats of the leatherback turtle during the nesting season in French Guiana

Understanding environmental cues determining behaviour and habitat use of species of conservation concern is crucial if one aims at implementing sustainable management of these natural resources. In this way, here, we investigate the thermal and trophic conditions encountered by the critically endangered leatherback sea turtle Dermochelys coriacea during its nesting season in French Guiana where high bycatch rates have been reported. Mean sea water temperatures obtained in situ by animal-borne recorders were 26.6 ± 0.7 °C in the water column, with all but one turtle remaining in water > 25 °C during the inter-nesting interval. In terms of prey availability, regular jellyfish stranding events were recorded during the nesting season, on a 1.25-km long section of the nesting beach. The occurrence of jellyfish was supported by benthic trawls performed on the continental shelf, with a total of 45.4 kg of jellyfish collected in 3.5 h exclusively in coastal waters 10 to 20 m deep where water transparency was between 0.8 and 3 m. This is consistent with the at sea distribution area of gravid leatherbacks during their inter-nesting intervals, as they spent almost 70% of their time diving in shallow (< 20 m deep) waters in front of the Maroni River estuary. In French Guiana, leatherback's gelatinous prey are thus present in very shallow water close to the nesting site and may be easily exploited by active gravid leatherbacks. This suggests that French Guiana female leatherbacks may be influenced by local trophic conditions and actively prospect productive areas overlapping with local fisheries ground.

Dispersal and dive patterns in gravid leatherback turtles during the nesting season in French Guiana

We present the first combined analysis of diving behaviour and dispersal data collected from gravid leatherback turtles during 3 consecutive nesting seasons in French Guiana. In total, 23 turtles were fitted with Argos satellite transmitters and 16 individuals (including 6 that were concur- rently satellite-tracked) were equipped with an electronic time-depth recorder for single inter- nesting intervals, i.e. between 2 consecutive ovi-positions. The leatherbacks dispersed over the con- tinental shelf—from the coastal zone to the shelf break—and moved over 546.2 ± 154.1 km (mean ± SD) in waters of French Guiana and neighbouring Suriname. They mostly performed shallow (9.4 ± 9.2 m) and short (4.4 ± 3.4 min) dives with a slight diurnal pattern. They dived deeper as they moved away from the coast, suggesting that they were predominantly following the seabed. Inter-nesting intervals could be divided into 2 phases: the first comprised 75% of the time turtles spent at sea, dur- ing which they dived on average 47 min h -1 , while the second was characterised by lower and more variable diving effort as the turtles returned to shore. The extended movements of leatherbacks and the fine analysis of dive shapes suggest that, in French Guiana, leatherbacks may feed during the inter-nesting interval, probably to compensate for the energy costs associated with reproduction. Consequently, this critically endangered species is exposed to a high risk of interaction with local fisheries over the continental shelf.

Respiratory frequency, dive behaviour and social interactions of leatherback turtles, Dermochelys coriacea during the inter-nesting interval

We collected simultaneous dive Time Depth Recorder (TDR) data and video images from free swimming adult female leatherback turtles, Dermochelys coriacea, during the first 24 h after nesting on the beach, in order to determine relationships between dive parameters, activity, overall respiratory frequency and behaviour. We identified three different underwater locomotory activities (subsurface swimming, V-shaped dives and U-shaped dives) from video and TDR data that varied in their mean depth, duration and a number of other parameters. Overall respiratory frequency (overall f R) was significantly different between all locomotory activities, with turtles taking 1.7±0.1 breaths min −1 while subsurface swimming, 0.78 breaths min −1 after V-shaped dives and 0.57 breaths min −1 after U-shaped dives. Descent rates and ascent rates were significantly faster in U-shaped dives (descent 0.19±0.010 m s −1, ascent 0.28±0.015 m s −1) than in V-shaped dives (descent 0.10±0.008 m s −1, ascent 0.12±0.012 m s −1). Flipper stroke rates were significantly lower during the bottom component of U-shaped dives (0.18±0.02 strokes s −1) than during the descent (0.29±0.03 strokes s −1) or ascent (0.29±0.03 strokes s −1). From overall f R and flipper stroke rate data, we inferred that turtles used less energy during U-shaped dives than the other activity types. We recorded interactions between male turtles and the study females that lasted up to 11 min, during which male turtles displayed the characteristic courtship behaviour of sea turtles. It appeared that females attempted to avoid males by aborting ascent and extending dive duration to swim to the sea floor when males were present.

Clutch Frequency in the Red-Eared Slider (Trachemys scripta elegans)

Clutch Frequency in the Red-Eared Slider (Trachemys scripta elegans)

Reptilian diving:highly variable dive patterns in the green turtle Chelonia mydas

Diving reptiles, unlike most diving birds and mammals, return infrequently to the surface to breathe. Spending the bulk of their lives underwater, they are likely to have developed a large variety of specific behavioural patterns different from those of their warm-blooded counterparts. However, for technical reasons, underwater behaviour of these aquatic reptiles remains poorly understood. In this study green turtles Chelonia mydas nesting on Cyprus (Eastern Mediterranean) were equipped with multi-channel data loggers monitoring diving behaviour and activity (via a logger-integrated 3-D compass which served as an activity sensor) during the inter-nesting interval. Data from 2 turtles for 2 consecutive inter-nesting intervals were available for detailed dive analysis. Both turtles showed highly variable dive patterns ranging from travelling subsurface dives to specific dive types such as U- (mainly resting and foraging dives), S- (a form of energy saving swimming) and V-dives. The green turtles stayed near the coast throughout the study, dived no deeper than ca 25 m, but remained underwater for up to ca 40 min. The recordings of the activity sensor revealed high activity levels (less than 20% resting d -1 ) during the whole inter-nesting period which was attributed to extensive foraging. The combination of both the activity data and the dive data showed that the turtles were engaged in travelling movements for 46 % of the inter-nesting time spent underwater, foraged for 34 % and rested for 12% of the time. We discuss the physiological, ecological and conservation implications of these results.

Breeding biology of the green turtle, Chelonia mydas, (Reptilia: Cheloniidae) on Wan-An Island, Peng-Hu Archipelago, Taiwan. I. Nesting ecology

The nesting season of the green turtle, Chelonia mydas on Wan-An Island, Peng-Hu Archipelago, Taiwan extended from early June to early October in both 1992 and 1993. Turtles nested on 9 of the 11 beaches on the island. The average inter-nesting interval was 14.9 d. A close relationship between the first reemergence time and the tidal cycle was found in the present study. The mean straight carapace length of the adult female was 96.6 cm. Female turtles produced from one to nine egg clutches; the average clutch size was 113 eggs. The mean egg size was 46.9 mm in diameter and 22.7 g in weight. The average incubation period was 49.3 d. The sediment characteristics of the beaches on the island are well within the incubation requirements for green turtle nesting. The average hatching success was 70%, but was lower in the artificial nest. The average size for hatchlings was 46.9 mm in straight carapace length and 22.7 g in body weight. The health of the hatchling is influenced by the adult female size, the nesting depth and the precipitation during incubation.