Figure 1 represents the time of sunrise according to the date and latitude. These times reflect the interaction (see Appendix S1 for details) of the change both in time of sun crossing the meridian and in the hour angle (a measure of how high the sun is at midday). The variation induced in sunrise increases throughout the year with the latitude. We can also GSK-3 inhibitor verify that shortly after 65° (when one reaches the polar circle at ±66°34′), both sunrise and sunset events happen at 12 (am or pm). Thus, a ‘day’ of complete light or darkness occurs. Using equations (1) and (2), it is possible to visualize the distribution of the modelled behaviour at any latitude and for any duration using either the ‘clock

time’ or ‘sun time’ method. These distributions may differ greatly between both methods, especially for prolonged studies and at high latitudes. Figure 2 illustrates this by

presenting the resulting distributions selleck chemical after recording a behaviour for 1 year at 45° latitude using both methods. In particular, the expected distribution of behaviour as a function of ‘sun time’ is independent of the latitude and study duration. The expected distribution of behaviour as a function of ‘clock time’ might reveal more about changes in sunrise than about the actual timing of the behaviour. We can then see the impact of the latitude by plotting the distribution of behaviour as a function of both ‘clock time’ and latitude (Fig. 3, isothipendyl equivalent to the solid curve in Fig. 2 for different latitudes). As expected, there is a general trend for the distribution to flatten at higher latitudes. It is clear from this graph that increasing the latitude will increase the amount of information loss, or noise, due to change in sunrise. Finally, using equation (3), we estimated the information

lost by using a clock time method rather than the more accurate sun time method. Figure 4 expresses the loss of information, or noise, according to the duration and the location of the study. We can observe that the noise increases as the latitude increases and as the standard deviation around sunrise decreases. The maximal amount of noise occurs when the study lasts for 6 months. Then, we observed a gradual gain in information as the sunrise occurs at the same time as in previous days. In conclusion, noise increases markedly with study duration and latitude. For instance, at 30° latitude, using clock time during a 6-month period, around 70% of the signal is lost due to noise (with σ = 0.25). The more spread the daily behavioural distribution (greater σ), the less noise results from using a ‘clock time’ method. Our comparison between behaviour time windows using both methods shows a significant difference in the obtained results: if the wrong method is used, the major prey items will be seen as being caught within the same time windows (F2,165 = 2.17, P = 0.18; see Fig. 5a).