Size and age distribution of white-tailed deer in Finland

A white-tailed deer male in its prime

Mikael Wikström (Suomen Riistakeskus), Jaana Kekkonen (University of Helsink) and I teamed up some years ago. We were initially interested in the genetic diversity of the white-tailed deer in Finland. In 2012, we contacted all hunting groups in the western part of Uusimaa (municipalities of Hanko, Raaspori and Inkoo) and the local hunters in this region supplied us with slaughter weights and the heads of 461 one.year old and older white-tailed deer hunted in the 2012-2013 hunting season. The total area covered was large and the number we obtained was 95% of all adult white-tailed deer hunted that season, so thanks to the dedication of the hunters to this project we obtained a sample which is pretty representative of hunted adult white-tailed deer in Finland.

After we got the heads, the lower jaw of all animals was removed. Heads of males were boiled and cleaned. In addition, we pulled a tooth from the lower jaw for ageing. Morphometric measures of the jaw and the skull were combined with CIC scores of antlers and body mass after slaughter. These metrics give us a fair idea of the size of white-tailed deer males and females in Finland. Comparison with North American data shows that Finnish white-tailed deer show no evidence of abnormal growth. If anything, the Finnish deer were a bit larger than in North America, probably because the density of white-tailed deer is much lower in Finland.

One perhaps worrying aspect of the research was that the hunted female deer were significantly older than the males. Our effort was the first time such information was collected in Finland and we are hence not sure whether this is a typical finding or something unusual to the 2012-13 hunting season in western Uusimaa. Extensive research in moose has underlined that a lack of old males is a bad thing for the population. When old males are lacking, females tend to mate later in the season as they are reluctant to mate with young guys! Reproducing late in the season, however, leads to small fawns and this has in turn a negative consequence on fawn survival and future growth.

As said, we do not know for sure if old males are lacking in the population. On the other hand, there is a pretty plausible reason for why the white-tailed deer population really would lack old males. This is because the hunting regulation rules in effect constitute a "life insurance" for females (they cannot be shot when they have fawns, and the number of licenses for adults can be increased by shooting less calves). Males lack such a "life insurance" and may thus run a greater risk to get shot during the hunting season. The hunting pressure on white.tailed deer is huge and hunting largely shapes the population characteristics. 

Given the reasonable ease by which one can collect lower jaws and use these for ageing, it feels to me that the methods we use in this paper could be used more in Finland. By repeatedly measuring ages of large numbers of hunted individuals in an area, we can - at the very least - start to get a feeling for whether the lack of older males is a recurring aspect. If it is, further research is warranted into understanding why these old males are lacking and what the consequences of such a skew in the age distribution could be.

8.4.2016: Jon Brommer


Links to earlier work on Finnish white-tailed deer

Genetic diversity

Inbreeding depression

Some text in Finnish or Swedish

The following articles in the magazine Metsästäjä /Jägaren can be found from here

Valkohäntäpeuran koon ja sarvien kehitys – ainutlaatuinen tutkimus lounaisella Uudellamaalla. Metsästäjä / Jägaren 5/2013: 32-34.

Suuri valkohäntäpeura-projekti Länsi-Uudellamaalla. Metsästäjä / Jägaren 6/2012: 8.

Suomen valkohäntäpeurakanta – geneettisesti hauras? Metsästäjä / Jägaren 3/2012: 38-40.