Where’s the Statistics?
After reading over and digesting Nelson’s (1998) “Development of migratory behaviour in northern white-tailed deer” the group had gradually come to the conclusion that the paper did not really belong in the otherwise good Canadian Journal of Zoology. The paper is very little more than a case study of the fates of 36 collared white-tail fawns. Case studies have their value, but the problem arose when they tried to translate this into hypothesis testing.
The study, in short, radio collared the affronted 36 fawns in the winter and followed their fates. They found that the majority of them returned with their mothers to their ‘natal summer ranges’ and a portion of those back-migrated to the same winter ground. Some deer dispersed to new summer grounds, and would back-migrate to a winter ground. Everything else in the paper is individual case summaries too tedious to recreate here.
The most glaring omission throughout this paper was that there was almost no statistics to speak of. I could only find one instance where I knew a confidence interval, and it was on a trivial value. Everything else is presented as percents, without any way of knowing if the differing value of percentages means the effects were significant. Secondly, we have no way of knowing whether the deer truly returned to their natal ranges – the author just assumes where they went after their first winter was their natal range. They collared the fawns at the wrong time of year to really wrap their head around the phenomenon. Finally, in the discussion, the author included unpublished data to bolster their own hypothesis. We were not overly impressed by this.
The big disappointment is that this topic is of general interest. Migratory behaviour in ungulates is understudied compared to birds, and many species that engage in migratory behaviour are of considerable human importance. It would be fascinating to repeat this study with fawns collared at birth (or soon after) to tease apart how white-tails establish their migratory behaviour in more mobile populations. This does not shed much, if any, light on the issue.
Nelson, M. (1998). Development of migratory behavior in northern white- tailed deer Canadian Journal of Zoology, 76 (3), 426-432 DOI: 10.1139/cjz-76-3-426