## 1 Introduction  
Animal transport is an important part of livestock production [1], with potentially negative consequences for animal health and welfare if not carried out correctly [2]. Issues such as the condition of the animal at the time of loading, loading density, time in transit, social stress, vibrations, handling, noises and smells, sudden speed changes, and ambient temperature [3; 4; 5] are potential stressors. Livestock animals are often transported by road, and sometimes by air, especially for breeders. One of the major stressors for animals during both types of transport is temperature (too low or too high) and significant thermal variations over short periods of time [6; 7; 8]. These events challenge the thermoregulatory response of animals that are usually already stressed due to handling in unfamiliar environments. Several studies have described the negative effects of high temperatures during transport, such as the risk of dehydration, weight loss, changes in behavior, reduction in food consumption, or changes in blood indicators, both in piglets [9] as in barrows and gilts [10]. Piglets transported under conditions of low temperature show a significant decrease in food consumption both during transport and for some days later [11]. Several other studies have also analyzed different \"animal-based measures\", such as skin temperature, heart rate, and salivary cortisol, to show how adult pigs cope with road transport under challenging environmental conditions [8; 12]. Few studies have compared thermal variabilities during air and road transport using the same animals, partly due to the lack of tools to compare thermal data from time series over periods of different duration. With the advent of smaller and longer-lasting temperature sensors, it is now feasible to record high-frequency time series for body temperatures [13] for extended periods, both on the farm [14] and during transport [15]. Sensors can be placed in different locations on or in the body to measure temperature without surgical intervention, such as the gastrointestinal tract [10], the vagina [16], and the ear canal adjacent to the tympan membrane. Of these three locations, the ear canal is considered the most convenient since it is easier to fix the sensors and they are not easily removed by the animals [17]. Specifically, for pigs, [PERSON] et al. [18] used small data loggers to provide continuous monitoring of ear skin temperature (EST), highlighting a diurnal rhythm with a maximum at night when the pigs were resting (more physical contact) and a minimum in the afternoon. Recently, our group has shown similar results over one-week supervision [19]. [PERSON] et al. [20] also suggest that EST is a good measure of the thermoregulatory response in pigs, providing a \"thermal window\" into changes in core body temperature since the ear is not heavily insulated, and [PERSON] [21] pointed out that skin temperature reflects the balance between metabolic heat production and the heat loss to the surroundings. It is assumed that pigs feel thermally comfortable at a specific skin temperature [18]; however, this thermoneutral zone changes over time, predominately as a function of body mass due to metabolic heat production and the decreasing surface area to mass ratio as animals grow [21]. Consequently, body mass should be considered as an input in the analysis of thermal dynamics. Few studies have compared thermal data from time series for pig EST. Handling time series with a high sampling frequency produces a large quantity of data which has led to the development of analytic procedures to try to extract more information than using methods based on basic statistics such as averages and variance. [PERSON] et al. [22] used fractal dimension methodology to objectively characterize stress responses in steers subjected to increasing severity of thermal environments. [PERSON] et al. [23] used a Fourier spectral analysis and short-time Fourier transforms to characterize tympan temperature in swine. [PERSON] et al.