A Rant about why Herd Structure Is So Important to Our Deer Herds

From: Wildlife Biologist & Sika Foundation Secretary – Cam Speedy

Hunters often ponder why stags do and don’t ‘roar’. They did roar this year, we just weren’t there to hear them because of Covid-19. But other years we hear all sorts of theories about why stags don’t roar: too hot, too dry, too late, too early, the wrong moon. The reality is that if the stags don’t roar very well on a hunting block, chances are there is probably a problem with herd structure. Herd structure is one of the most important aspects of game management – one that has a huge influence on rutting activity/intensity, reproductive output, environmental impact, and general herd performance.

So what is ‘herd structure’? Here’s the simple answer – it is the relative proportions of the different age and sex classes of animal in a game population. Most game animals are born in equal proportions of male and female – or near enough – usually about 510–520 males to 480–490 females per thousand offspring. The potential life expectancy of individuals in most game species is 10–15 years, so over the life of each age cohort the various environmental influences to which the herd is exposed will generate a range of possible herd structure outcomes depending on the survival or mortality of different individuals. These influences might include:

·   Climatic events (e.g., drought, snow, floods)

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·   Land or habitat management activities (e.g., fire and pest control)

·   Habitat quality (there is not much to eat in a hollowed out beech forest!)

·   Predators (e.g., dogs)

·   Geological events (e.g., eruptions, earthquakes)

·   Hunting/harvest 

Without a doubt, the biggest influence on a deer herd is human hunting activity. Stags and hinds might be born equal, but once human harvest regimes kick in, their relative proportions change dramatically year on year. In a New Zealand context that hunting influence might include: commercial Wild Animal Recovery Operations (WARO), Department of Conservation funded culling, aerial assisted trophy hunting, and recreational hunting, or any mix of all four (Note: I am not going to get into the 1080 debate here).

The sex and age specific behaviours of deer, and the powerful selective forces various hunting influences have on a herd, hugely affect herd structure within our New Zealand deer herds. Critically, young stags are extremely vulnerable when they leave their mothers in the ‘breeding’ country to seek the company of other stags that live much of the year in bachelor groups in high quality (often open) feed areas: the ‘fattening’ country. Their naïve behaviour, limited life skills, sudden lack of maternal supervision, extremely visible open habitat, and the heavy preference from both recreational and commercial hunting sectors to remove males, results in a large and chronic over-harvest of young stags. In contrast, females are targeted to a much lesser degree by most hunting regimes, and their preference for shelter cover over much of the year to raise and protect fawns makes them – and their resident offspring – far less vulnerable.

Figure 1 shows a typical herd structure for a heavily exploited deer herd in New Zealand.   Note that survival of young stags in the 1+ and 2+ year classes is extremely low. These are the spikers that form the majority of the New Zealand Christmas BBQ venison order and the young adult velvet stags that make up the vast majority of our pre-Christmas wild venison export shipments. Additional to this, poor 1+ and 2+ stag survival in spring is a result of the heavy harvest selection of 3+ and 4+ stags every rut by recreational hunters – those small 8–10 pointers that rush so readily and carelessly into a hunter’s roar. It’s not hard to see why most wild New Zealand deer herds have herd structures characterised by an absence of mature (6+) stags – dead stags don’t grow. The result is sex ratios that heavily favour females: 65 females to 35 males for every 100 deer in most of our herds.

The upshot of this is that our herds are highly productive, at least where the habitat remains healthy, reproducing at an excess of 45% per annum (almost doubling every two years).  However, because the intensity of rutting behaviour is governed by the level of competition between males, the ‘roar’ tends to be very poor under such situations. A few adult males sharing lots of females does not result in particularly exciting roar hunting. More poor young stags also get to pass on their genes. Trophy production is also limited – even where habitats provide good nutrition – since so few males reach trophy age classes. 

Even more damaging is that, due to their more sedentary lifestyles, the greater the proportion of females in the herd, the more environmental impact the herd will inflict on the habitat. Female-led family groups occupy home ranges 3–10 times smaller than males depending on species (eg., 100ha–200ha for sika hinds vs. 600ha–1,000ha for sika stags).  All the environmental impact of female family groups is concentrated on small areas of breeding habitat. As herds expand with high proportions of females, habitat impact then starts to affect deer quality. Hinds stop breeding every year, and the lack of ‘hot fanny’ reduces the intensity of the rut even further. More importantly, when your deer habitat is public conservation land with high native biodiversity value, this can bring deer hunting into conflict with other land values.

An approach that has been developed in the USA since the mid-1970s to manage the negative aspects of female dominated herd structures is ‘Quality Deer Management’ (QDM). QDM advocates for greater restraint in the harvest of 1+ and 2+ males and a far greater harvest of females. The herd structure that develops – very quickly – under such a regime is shown in Figure 2. Note that the sex ratio is far more balanced (1:1) as a result of shifting the harvest pressure off the 1+ and 2+ males onto the female components of the herd, thereby limiting deer density to levels that can be better sustained by the habitat. Male survival also increases allowing far more males to mature. Annual herd output falls to a more modest 30%–35% per annum (doubling every 3 years) due to the lower proportion of females. But this lower proportion of females, living in more sustainable habitats, also greatly increases the fawning rates of individual females. This leads to greater competition between more males for the fewer hinds on offer, and all the fanny is hot because the females are in good nick. The quality of the rut hunting improves significantly with an increase in rut activity/intensity. Larger, stronger males also dominate gene flow, suppressing the contribution of younger or poorer quality males to the next generation.

Roar hunting on a QDM hunting block is truly exciting and the chances of a trophy are greatly enhanced with more males in older, trophy age classes. From a habitat perspective, a herd structure such as shown in Figure 2 will also inflict less environmental impact.

Where habitat impact by a deer herd is a potentially significant issue, another herd structure that could be pursued is shown in Figure 3: Trophy Management. This approach heavily targets females and actively protects males until they are mature. The reproductive rate of such a herd will fall as low as 20%–25% per annum (doubling every four years) as the males out-number the females, which makes the herd much easier to control. This is a low deer-density approach (2–3 deer per km²), so large areas are required to allow for viable herds to exist. Some males disperse due to the intense competition between potential sires and a larger proportion die from fighting during intense rutting activity. However, the low density allows maximum nutrition and it is, therefore, an approach that can produce outstanding trophy hunting opportunities. In my view, this approach has considerable merit in many areas of public conservation land in New Zealand where a low density, low impact, high quality trophy resource might be more compatible with conservation values. The best example is the Fiordland wapiti herd. Such an outcome requires extremely careful management to ensure it is female focused and that young males (less than 5 years old) are given the protection they need. It cannot occur unless the harvest is tightly controlled.  

Tragically, current harvest regimes on public conservation land in New Zealand remain totally uncontrolled except in a very few, tenuous, select locations. Even more ironic is that Conservation NGOs and therefore, large factions within the Department of Conservation, refuse to accept that ‘active game management’ regimes might actually achieve better conservation outcomes than the current ‘default’ regime – much of which is driven by fickle, international commodity prices and currency exchange rates. And they tend to target males – a lose-lose for conservation and hunting. 

There is no right or wrong approach to game management. Game management is an active process that seeks to achieve specified outcomes. The management approach will totally depend on the outcome being sought. In New Zealand, where most herds are not subject to any ‘active’ management towards a specific outcome, the default herd structure that tends to develop is similar to that shown in Figure 1. This can lead to damaged forests, skinny deer, poor trophies and generally poor hunting outcomes – outcomes evident today in places like Raukumara and parts of the Kaimanawa high country. These are lose-lose outcomes for both hunting and conservation.

Yet, the perception still remains amongst far too many hunters that they should not shoot hinds and that stag-only harvesting will take them to some sort of hunting El Dorado.  Nothing could be further from the truth. Protecting hinds only makes sense when deer are at very low densities and there is a desire to increase the population; or seasonally if they have fawns at foot for obvious animal welfare reasons. In my view, June to October on most New Zealand forest and mountain land should see female game animals getting hammered. There are more deer in New Zealand today than at any time in my 40-year-hunting-career. Continuing to protect females and allowing herds to grow to unsustainable levels will only result in agencies like DOC or Regional Councils stepping in and taking their own action. That action might not be in the best interests of hunters or hunting. Remember the tahr issue?

So, if we are allowed to hunt next roar and the stags are a bit quiet on your hunting block, have a think about what influences your deer herd. Maybe it is suffering from poor herd structure? How many hinds were there? Were they fat? How cleaned out was the bush?  Maybe your harvest selections could start to change a little to help those situations? If everyone made a small change, what a difference – biologically – we could all make.  

And if hunters were seen less as end-use consumers of deer with a self-interested sense of entitlement, and more as guardians of our forest and mountain-lands with a strong sense of collective responsibility, what a difference – politically – that might make?

Food for thought …

Images:

Figure 1:      See .ppt 

Photo 1: This image of an old, small, skinny sika hind (1 of 18,000 deer images) captured as part of a recent Landcare Research/Sika Foundation Camera Survey in the Kaimanawa Rangitikei REZ. Many of the hind images captured looked like this – or worse. Very few fawns were captured on film, despite the survey running from mid-Dec 2019 to late-Feb 2020. This situation is a lose-lose for both conservation and hunting.

Photo 2: This Gary Harwood image of a fat, healthy, reproductive sika hind comes from Clements Road. Healthy habitat is what produces healthy, sustainable deer herds. 

Bar Room Brawl – Roar Analogy 

Imagine there’s an old pub in the country on a Friday arvo with two females having a drink while feeling good and looking good. Then 20 blokes walk in who have just finished a hard day’s sheering and are thirsty for a beer. After a few beers the shearers start making moves on the girls. The guys get scrappy over them and before you know it, there’s an all out brawl between the guys to take one of these ladies home. Funnily enough, this is how a well managed herd structure should perform.

But say the Kiwi Express pulls up and about 40 female tourists come into the bar … All of a sudden these blokes have more females than they know what to do with. So there’s really no need for a brawl to win over the ladies. Although these guys are pretty happy with the situation, this is what bad herd structure would look like for deer. And just like the country shearers, the stags may not be as active and loud during the roar.