Research Article |
Corresponding author: Lukáš Weber ( lukas.weber@seznam.cz ) Academic editor: Lukas Landler
© 2023 Lukáš Weber, Jan Růžička, Ivan H. Tuf, Martin Rulík.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Weber L, Růžička J, Tuf IH, Rulík M (2023) Migration strategy of the Great crested newt (Triturus cristatus) in an artificial pond. Herpetozoa 36: 345-356. https://doi.org/10.3897/herpetozoa.36.e112826
|
In animals, migration is an evolutionary adaptation to manage seasonally varying habitats. Often driven by climatic changes or resource availability, amphibians then migrate from their hibernation sites to their breeding grounds. This research focused on the migratory habits of the Great crested newt (Triturus cristatus). The study explored factors like gender, body size, and environmental determinants, noting that immigration and emigration events proved distinct during the year. Results unveiled that males typically reached ponds first, with temperature being pivotal: males preferred up to 5 °C, females around 10 °C, while juveniles moved as temperatures increase. Wind velocity affected larger newts, around 120 mm, prompting them to migrate with stronger winds. Notably, heavy rainfall favored migration of newts of roughly 60 mm size. Humidity displayed gender-based trends: males associated positively with average levels, females showed aversion above 50%, and juveniles leaned towards drier conditions. Emigration patterns mirrored these findings, emphasizing roles of temperature, wind, and humidity. The effect of moonlight is not statistically significant. These findings provide valuable insights into the environmental factors influencing the migration of T. cristatus, which may guide future conservation efforts.
Bei Tieren ist die Migration eine evolutionäre Anpassung an saisonal wechselnde Lebensräume. Oft sind es klimatische Veränderungen oder die Verfügbarkeit von Ressourcen, die dazu führen, dass Amphibien von ihren Überwinterungsplätzen zu ihren Brutgebieten wandern. Diese Studie befasste sich mit den Wanderungsgewohnheiten des Kammmolchs (Triturus cristatus). Die Studie untersuchte Faktoren wie Geschlecht, Körpergröße und Umweltfaktoren und stellte fest, dass sich Ein- und Auswanderungsereignisse im Laufe des Jahres unterscheiden. Die Ergebnisse zeigten, dass die Männchen in der Regel zuerst die Teiche erreichten, wobei die Temperatur ausschlaggebend war: Die Männchen bevorzugten Temperaturen bis zu 5 °C, die Weibchen etwa 10 °C, während die Jungtiere mit steigenden Temperaturen abwanderten. Die Windgeschwindigkeit wirkte sich auf größere Molche (ca. 120 mm) aus und veranlasste sie, bei stärkerem Wind zu wandern. Vor allem Molche mit einer Größe von etwa 60 mm bevorzugten bei ihrer Wanderung starke Regenfälle. Die Luftfeuchtigkeit zeigte geschlechtsspezifische Tendenzen: Männchen assoziierten sich positiv mit durchschnittlichen Werten, Weibchen zeigten eine Abneigung gegen Werte über 50%, und Jungtiere neigten zu trockeneren Bedingungen. Die Auswanderungsmuster spiegeln diese Ergebnisse wider und unterstreichen die Rolle von Temperatur, Wind und Feuchtigkeit. Der Einfluss des Mondlichts ist statistisch nicht signifikant. Diese Ergebnisse bieten wertvolle Einblicke in die Umweltfaktoren, die die Migration von T. cristatus beeinflussen, und können als Grundlage für künftige Schutzbemühungen dienen.
emigration, immigration, moon phase, rainfall, temperature, Triturus cristatus, wind
Auswanderung, Einwanderung, Mondphase, Niederschlag, Temperatur, Triturus cristatus, Wind
Migration is an adaptive behavior seen in animals that enables them to deal with environments that change seasonally (
It’s worth mentioning that the migration of newts, including crested newts, is not a synchronized process, and individuals can be seen migrating several months after their initial arrival at the pond (
Adults of various species frequently display non-random migration patterns when departing from breeding sites, illustrating a propensity to both enter and exit the same locations and expressing a preference for specific habitats as transit routes over others (
Our study was centred on immigration and emigration activity of T. cristatus. The research was conducted at a location known for its suitability to T. cristatus and where these species have been documented in the past (
The research was conducted in the artificial pond located in Czech Republic in the village of Tovéř (49°38.433'N, 17°19.691'E), which is situated northeast of the town of Olomouc at an elevation of 227 meters above sea level. This pond is a small retention reservoir with a water surface area of approximately 500 m2. Since it lacks a permanent water inflow, its water levels are dependent on current rainfall, the usual depth in spring is 1.8 m, sometimes in warm summers it completely dries up. The pond was eutrophic with algal growth on the surface. From the south and northeast sides, the shore of the pond has a gentle slope. The littoral zone of the pond is mainly dominated by pondweed (Lemna minor), and submerged grasses are also present in the area surrounding the pond. Based on the Habitat Suitability Index (HSI) assessment, which evaluates the suitability of habitats for the occurrence of T. cristatus, the Tovéř locality is classified as “good”. The water body does not contain any fish. However, waterfowl, particularly mallards (Anas platyrhynchos), can be found in the area. One of the potential amphibian predators present at the site is the grass snake (Natrix natrix). In addition to the great crested newt, other syntopic amphibian species found here include the common newt (Lissotriton vulgaris) and the alpine newt (Ichthyosaura alpestris). The fire salamander (Salamandra salamandra) has also been observed in the vicinity. Among the frogs, individuals of the European fire-bellied toad (Bombina bombina), the European tree frog (Hyla arborea), the common toad (Bufo bufo), the European green toad (Bufotes viridis), and the agile frog (Rana dalmatina) have been captured in this area.
The monitoring took place from 4 March to 18 November 2017, for a total of 259 days. During this study, amphibians were captured using drift fencing lined with pitfall traps (n=47) around the whole pond. The 75 cm high PE (polyethylene) UV-resistant half-sheet was used as a guidance drift fence during the study. Approximately 10 cm of the drift fence was embedded in the ground to prevent individuals from burrowing under the barrier. As part of the trapping method, white plastic buckets measuring 30 cm in height and 25 cm in diameter were buried around the perimeter of the pond as traps. These trapping buckets were spaced approximately 3 meters apart and were sunk into the ground so that the top of the bucket was level with the ground (
The effect of meteorological data on migration activity of different body size and both sexes were evaluated using Canonical Correspondence Analysis (CCA) using Canoco for Windows 5.0. Models for both immigration as well as emigration activity of newts were done. Body size and sexes were used as species data, whereas environmental data were factors: week of the year (week), average temperature (T_avg), minimum temperature (T_min), maximum temperature (T_max), average wind strength (F_avg), maximum wind strength (F_max), precipitation (SRA), average humidity (H_avg), direction from forest (forest) and length of sunshine (light). Environmental variables that significantly explained variation of activity of newts were uses to calculate predictive Generalized Additive Models (GAM). The direction of migration (both immigration and emigration) was visualized in program Oriana for Windows with applied Rayleigh-Test.
During the immigration process, the highest number of captures was observed for males, with 543 individuals recorded. Females followed closely with 532 captures, while only 21 juveniles were observed arriving in the pond. In terms of emigration, 530 males, 386 females, and 191 juveniles were recorded as captures. The sex ratio of T. cristatus individuals found at the Tovéř site was 1.21:1, with a slight majority of males compared to females. The primary immigration of T. cristatus to the study site, accounting for 75.36% of the total number of immigrants, occurred between March 4th and March 31st, spanning a period of 27 days. During this period, a total of 390 females (accounting for 73.31% of the total arrivals), 433 males (79.74%), and 3 juveniles (14.29%) arrived at the study site. A subsequent small increase in immigration was observed from around April 28th to May 8th. On the other hand, the primary emigration period for individuals began on June 5th and lasted until July 12th, totalling 37 days. During this time, approximately 40.43% of the overall outmigration was attributed to the leaving individuals. During this period, 336 females (representing 87.05% of the total number of females leaving) and 421 males (79.14%) departed. However, no juveniles were observed to emigrate during this period. The juveniles experienced an emigration wave from August 7th to September 6th (n=130; i.e., 68%), followed by a shorter period from September 15th to September 27th. Autumn migrations of tens of individuals have also been recorded. T. cristatus individuals were observed immigrating to the pond predominantly from the southwest, which includes village area (Rayleigh test; mean direction ± IC95 is µ=215.111±11.27°; length of vector r=0.211; p<0.0001). Conversely, during emigration, individuals predominantly departed to the southeast, where the forest is situated (Rayleigh test; µ=148.598±8.84°; r=0.265; p<0.0001) (Fig.
When examining the direction of immigration separately for each sex, we find that for females (Rayleigh test; µ=209.735±17.43°; r=0.196; p=0.510) and juveniles (Rayleigh test; µ=39.639±67.54°; r=0.153; p=0.616), the results are non-significant, indicating no clear preference. However, for males, there is a significant preference (Rayleigh test; µ=219.5±13.94°; r=0.241; p<0.0001) that aligns with the overall direction of immigration, indicating a preference for coming from the southeast, which corresponds to the direction from the village (Fig.
The average length (SVL) of the male individuals captured during the study was 102.3 mm, while the average size of the female individuals was 108.4 mm. The average length for juveniles was 61.1 mm (Table
Size structure (SVL) in mm for immigration and emigration (Q1 = lower quartile, Q3 = upper quartile, med = median).
sex | Immigration | Emigration | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
max | min | med | Q1 | Q3 | max | min | med | Q1 | Q3 | |
female | 141 | 60 | 105 | 98 | 115 | 142 | 78 | 112 | 105 | 117 |
male | 124 | 54 | 99 | 92 | 105 | 126 | 10 | 106 | 102 | 110 |
juvenile | 70 | 48 | 62 | 59 | 68 | 76 | 39 | 62 | 56 | 66 |
The highest number of females (n=149) immigrated in the length of around 100 mm; the highest number of males (n=152) also immigrated in this length. As for juveniles, the highest number (n=11) was observed with the SVL around 60 mm. For emigration, both males and females shifted up by one average length. Most females (n=152) emigrated in body size around 110 mm, followed by 242 males in the same size. Among juveniles, SVL around 60 mm was the most preferred size, with 84 captures.
The Canonical Correspondence Analysis (CCA) model, when applied to single environmental factors during immigration, displays explanatory variables accounting for 8.8%. It highlights several influential factors under simple term effects, including week of the year, average, minimum and maximum temperature, average humidity and length of sunshine. No notable preference for these factors is observed among males and females. However, the immigration of juveniles is seen to be dependent on the week of the year and males immigrate to the pond at lower temperatures (Fig.
In the Generalized Additive Model (GAM) for the sequence of the week of the year, it’s observed that males arrive first at the pond, followed by females. Juveniles started immigration around mid-year. One of the key factors here is the average temperature, as the GAM indicates that females predominantly arrive at around 10 °C, males prefer cooler temperatures up to 5 °C, and the number of juveniles was observed to increase as the temperature rises from 10 °C. The GAM for minimum and maximum temperature were similar as GAM for average temperature. Males show a positive correlation with average humidity, whereas females display a negative correlation when humidity levels are 50% or higher. Juveniles seem to prefer lower humidity (Fig.
The Canonical Correspondence Analysis (CCA) model applied to individual environmental factors during emigration accounts for 26.15% of the variation. The significant factors within simple term effects include the week of the year, maximum and average wind strength, precipitation, average humidity, length of sunshine and minimum, maximum, and average temperature. In this model, males emigrated from the pond during lower rainfall, stronger winds on warmer days. Females emigrated on sunny days with warmer temperatures. For juveniles, the week of the year was important and they emigrated at higher humidity and precipitation (Fig.
CCA model for emigration for sex with the environmental factors (the week in year (week), average temperature (T_mean), minimum temperature (T_min), maximum wind strength (wind_max), average wind strength (wind_mean), average humidity (H_mean), precipitation (precipitation), light (light). Only significant variables are shown.
The Generalized Additive Model (GAM) for the order of week in the year reveals that males typically emigrated by the 25th week, followed by a decrease in emigration and a new surge starting around the 35th week. Females peak in their emigration around 20th week and then start their emigration again in the 35th week. Juveniles have an emigration peak during the 35th week. Male emigration decreases with increasing mean temperature, showing a slightly increase at 20 °C, while females prefer temperatures between 15–20 °C for their emigration. Juvenile emigration firstly decreases up to 20 °C, then increases with rising temperatures. The GAM for minimum temperature mirrors that of the mean temperature, with males preferring cooler temperatures for emigration, females around 15 °C, and juveniles leaving as the minimum temperature rises. In the GAM for maximum and mean wind strength, males tend to favour stronger winds for emigration, whereas females cease their migration at higher wind strengths. In terms of precipitation, juveniles tend to emigrate during heavier rainfall, while females and males demonstrate a decrease in emigration during such conditions. Regarding humidity, males find it optimal to emigrate around 60% average humidity, while females cease emigration as humidity increases. Contrarily, juvenile emigration elevates with increasing humidity (Fig.
The last factor we investigated was the impact of the lunar phase (illumination). We noted that as the moon’s phase or brightness increased, there was a rise in the number of both immigrants and emigrants, encompassing all genders. Nevertheless, the correlation discovered between moonlight and both immigration and emigration proved to be statistically non-significant. For immigration, we found a correlation coefficient r = 0.42, but with a p-value of 0.5, being not statistically significant. Similarly, the correlation for emigration was also statistically non-significant, with a correlation coefficient r = 0.049 and a p-value of 0.53 (Fig.
Our study noted that the major immigration period occurred between March 4th and March 31st. This accounted for a significant 75.36% of the total immigration events, over a period of 27 days. This immigration period is somewhat earlier compared to study (
In our study, we observed that the main emigration period began on June 5th and ended on July 12th, spanning a total of 37 days. This period accounted for roughly 40.43% of the overall outmigration, with individuals predominantly leaving during this time. Interestingly, no juveniles were noted to emigrate during this primary emigration phase. Instead, we recorded a significant juvenile emigration wave from August 7th to September 6th, during which approximately 68% (n=130) of the juveniles left. This was followed by a secondary, shorter wave from September 15th to September 27th. Autumn immigration suggests that certain individuals remain in the habitat over the winter period, indicating potential overwintering within the water. This finding may help to explain the phenomenon noted by
Our findings suggest that migration directions of T. cristatus individuals can be influenced by the presence of specific environmental factors such as developed land, forests, and possibly the shelters that gardens provide during the terrestrial period. The use of gardens in the village’s area as overwintering sites is intriguing and shows that these amphibians can adapt to utilize human-modified habitats for their survival needs. This adaptability can provide crucial survival strategies in a rapidly changing world where natural habitats are increasingly being modified or lost. However, there is also evidence to suggest that T. cristatus may not necessarily exhibit directional preference when moving to and from a pond (
Our results confirm that females are generally larger than males. This concurs with the findings in study
Our study found that female T. cristatus tend to start their migration at around 10 °C, while males seem to prefer cooler temperatures of up to 5 °C, and juveniles start their migration as temperatures increase. Initial migrations occur post-sunset at temperatures above 4–5 °C, with most activity during consecutive humid nights (
Our research reveals complex connections between weather conditions and the migratory behaviours of T. cristatus. We discovered that rainfall and humidity play substantial roles in influencing behaviours, but their effects vary across different body size and genders. For example, newts between 50 and 70 mm prefer heavier rainfall, while larger newts decreases their arrival frequency with increasing rainfall. Our data also imply that precipitation affects emigration patterns, with juveniles tending to emigrate during heavier rainfall, while both genders show decreased emigration under such conditions. Juvenile amphibians, due to their smaller size and resultant greater surface area to volume ratios, are theoretically more prone to desiccation risks during day-time migrations compared to their adult counterparts (
While our findings did not display a significant correlation between the moon’s phase and immigration/emigration numbers, it’s worth noting that we haven’t considered possible interference from cloud cover. Clouds can obscure the moon’s illumination and thus might impact the activity patterns of the animals, or human activity in this case. This could be a relevant factor that may affect the visibility of the moon and hence potentially influence our observed results. Future research could explore this aspect to gain a more comprehensive understanding of the influence of lunar phases on migration patterns. There have been previous studies showing that the moon’s phase can affect the behavior of certain species. By
Finally, our study underscores that climatic conditions may play a crucial role in the migratory behaviours of T. cristatus as notable amphibian species. The documented decline in amphibian populations worldwide might be directly or indirectly associated with climate change, considering that key climatic elements like precipitation and temperature significantly influence essential processes in amphibian population dynamics (
Our study provides a comprehensive examination of the migratory patterns of T. cristatus, noting that a significant portion of immigration events occur over a period of 27 days, starting from March 4th. Our data align with previous studies, revealing similar migration patterns. Protandry, with males reaching breeding grounds before females, was observed, indicating potential mate selection advantages. Emigration was prevalent during a 37-day period from June 5th, while juveniles mainly emigrated from August to September. Autumn migration with overwintering within water habitats was also confirmed. In addition, the influence of environmental factors such as land development, forests, and human-made shelters was noted on migration directions. T. cristatus showed the ability to adapt to human-modified habitats. However, juveniles demonstrated non-preferred migration directions, indicating the influence of local habitat structure and resources. Temperature played a significant role in migration, with gender and size-specific preferences. Furthermore, rainfall and humidity considerably influenced migratory behaviours with variable effects across different sizes and genders. Our data suggested no significant correlation between moonlight and immigration/emigration, although an upward trend was observed. More research, considering factors like cloud cover, is suggested to understand this aspect better. Finally, the study emphasized the crucial influence of climatic conditions on amphibian migration, underscoring the need for further research and effective conservation strategies amid global climate change.
The authors thank the Palacký University Olomouc for providing financial support of our project (IGA_PrF_2018_020, IGA_PrF_2019_021, IGA_PrF_2020_020). We would also like to thank Dr. Matthew Sweeney for language correction. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed.