Author:

Abstract:

In behavioral research a variety of intervals is used when applying instantaneous scan sampling. To obtain an appropriate interval between two succeeding scans, time intervals should not be too long to avoid wasting time and inaccurate results. Adversely, time intervals should not be too short either, to avoid reduced observers alertness and reliability and to avoid dependence between successive data-points. Calculating mean bout lengths and standard deviations to determine the distribution of mean bout lengths is one solution. Another solution is suggested by Engel (1997) starting from a small continuously scored dataset. We used this method to evaluate the sample interval to score the activity budget and habitat use of two grazer species - Konik horses and Scottish Highland cattle - in a Belgian coastal dune reserve (see also Lamoot et al., 2004). For 127 focals of 900 seconds with continuous scoring, a data entry was made every second on ingestive and locomotory behaviour states, vegetation types of the area and consumed food type. From this continuous protocol a lot of instantaneous pseudo-protocols are derived, each one with a longer sample interval than its predecessor. The relative frequency of the behaviour pattern under investigation in the continuous protocol and every pseudo-protocol is computed and the dependence between each data point is calculated. The optimum sample interval is graphically derived from on the one hand, the association of pseudo-protocols with different intervals and the continuous protocol (Spearman rank correlation coefficients) and on the other hand, the mean probability of sampling the behaviour statistically independent. The compromise for the optimal intervals of all the scored behavioural states, vegetation and food types was on average 90 seconds.