Bokdam, J.

Prins, H.H.T.

English

Wageningen Yield 

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IV. HABITAT ÜSE OF WILD UNGULATES: DISCUSSION 
H.H.T. Prins and J. Bokdam 
Introduction 
Many methods for the measurement of habitat use were discussed, but two 
received the most attention, i.e., faecal pellet counting and direct 
observation. The discussion touched several times on problems concerned 
with the measurement of food intake, diet selection, and impact on the 
vegetation. The importance of defining in advance what one wants to know 
and why one wants to know it was underlined, because these two questions 
determine to a large extent the choice of methods for the research. 
Methodology concerns the selection of the study site, the study popula­
tion, the parameters, and the sampling methods. Extrapolation from one 
study area to other areas is impossible without experimentation, because 
otherwise the causality of the processes cannot be understood: a des­
cription of habitat use by a study population alone will not yield 
enough information to provide a model of even the study site itself, let 
alone to serve for predictions concerning other sites. The discussion 
dealt with methods that can be used: 
I. to assess the occupancy of the habitat by the animal species under 
study; 
II. to assess food intake or to arrive at a description of the diet 
of the animals in question; 
Ilia, to assess the amount of food on offer and the impact of these 
consumers on the vegetation and, b. on the use of the phenological 
calendar. 
The discussion dealt primarily with wild ungulates, but parts were 
also valuable for free-ranging domestic animals. The methods discussed 
can be divided into two groups, viz., direct methods in which direct 
visual or other contact with the animal to be observed is used to 
establish its presence or activity and indirect methods, in which traces 
of various kinds are interpreted as indicating presence or activity. 
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Direct methods 
Visual observation 
It was generally felt that direct visual observation of the species 
under study is the best way to collect reliable information about habi­
tat use, food selection, etc. Even when telemetry is feasible, it should 
be used in conjunction with direct visual observation for control. 
Several direct visual methods were discussed, roughly divided according 
to sit-and-wait and search-and-follow. With the sit-and-wait method a 
hide is erected and the observer remains in it as long as necessary. 
Only when the density of animals is quite high, the chance that one will 
observe the animals quite good; at low density 'you will sit and see 
nothing'. It was pointed out that one major drawback of this method is 
that the selection of sites for the hides will introduce a stong bias 
against the presence of all habitat types. Nevertheless, it can provide 
excellent information in some open types of habitat. The method can also 
be used at night with night vision equipment (and if necessary with 
infra-red floodlighting). 
The search-and-follow method is strongly dependent on the habitat 
type (e.g., inapplicable if too steep or too densely vegetated) and on 
the wariness of the animals. The search-and-follow method is easily 
biased • and to an unknown degree - by the disturbance caused by the 
observer. Observation from a vehicle is preferable but the observer 
should never use the same type of vehicle as the hunters employ. 
Cessation of hunting is recommended for a study area where direct 
observation is to be carried out; sometimes animals (e.g. deer) react 
quickly, becoming tamer (Ireland after the Chernobyl fall out), but in 
many areas they take a long time to do so. It was suggested that admit­
tance of the general public (without dogs) could promote tameness of the 
study population. A last resort could be observation on horseback. 
Observers should arrange to be as comfortable as possible (a nice 
temperature for working and a comfortable place to sit), because there 
is a strong correlation between the quality of the observations and the 
comfort of the observer(s). Nocturnal observations do not pose a problem 
if one is seated in a vehicle or in a hide. Many animals quickly become 
accustomed to spotlight, and night vision equipment gives good results, 
but moving around is more difficult at night. Telemetry can help to 
locate the animals. It is not clear why some populations have nocturnal 
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feeding habits and other diurnal. There Is no reason to expect a quick 
change from nocturnal to diurnal If hunting Is stopped In a study area. 
The easiest way to solve this problem Is to find another population 
which Is not nocturnal; If that Is Impossible, the difficulty must be 
coped with In some other way. 
Visual marking of individuals 
Individual recognition is not only imperative for studies involving the 
social organization of the population, but also for dealing with 
problems of biased sampling (e.g., good data on food selection might 
concern some tame deer happening to use a specific habitat type that is 
hardly used by the majority of the population). An attempt should 
therefore be made by preference to mark all individuals of a population 
(or use natural markings) but this marking system means having to 
capture the animals. Faint spraying or paint shooting was not discussed, 
but these methods may give good results too. Patterns of movement can 
only be studied if a number of individuals have been marked, and 
'radio-marking' of individuals can also serve this purpose. 
* 
Radio-marking of individuals 
After individuals have been caught they can be tagged and fitted with 
transponders. In connection with the present discussion on habitat use, 
it was agreed that telemetric methods can determine where the indivi­
duals are at a given moment with some precision, but will tell nothing 
about why the animals are there; furthermore, it remains doubtful 
whether they will supply enough information about what the animals are 
doing there. Some felt that with sufficient effort enough information 
can be obtained with telemetry if heart rate, head up/down movements, 
number of bites, etc., are recorded with different sensors. It was 
emphasized that one should strive to collect data that can be analysed 
in a straightforward fashion and with statistical methods. 
Other participants were more catholic in their approach, and pointed 
out that one ends up with many notebooks full of 'data' that are impos­
sible to analyse ('two roomfulls of collected and unanalysed data for 
each publication'). Although the majority agreed that this was a valid 
point, they preferred to use notebooks because they needed them later on 
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AuComlzed radiotracking demands major investments of time and money. 
for their analysis of the numerical data. Moreover, they did not believe 
that any telemetry system will function all of the time, so they felt a 
need for the back-up system supplied by their notebooks. 
It also was remarked that the social structure of a group of animals 
is often habitat dependent (e.g., small groups in closed habitat, larger 
ones in open habitats). Thus, if one relied exclusively on telemetry and 
only a few individuals had been fitted out or could be tracked, erro­
neous information would be obtained about habitat use by the population 
as a whole. As capturing of all individuals or getting all transponders 
to work is unlikely, 'old-fashioned' methods must be relied on as well. 
Indirect methods 
Hoofprints 
One of the so-called old-fashioned methods is to look for tracks left by 
the animals. If there is an extensive network of unmetalled roads in the 
study area one could consider tying brushwood (e.g., Crataegus, Prunus 
spinosa) on the rear of a vehicle to obliterate old tracks so one could 
check for new tracks every day. If these roads lie along the perimeter 
of different habitats, the tracks left by the animals could yield some 
information about the differential use of the habitats. However, the 
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number of tracks is not dependably correlated with such items as per­
centage of habitat occupancy or of time spent in different habitats, and 
therefore the data will give only a general idea about habitat use by 
the population. The 'track method' can nevertheless supply additional 
information in some study areas. 
Dung depositions 
In this respect, too, the group had grave reservations about the use­
fulness of methods based on the distribution of faecal pellet groups and 
interpretation concerning the habitat occupancy. Droppings tell where 
animals have defaecated, but the interpretation of dung densities in 
different habitats is not simple. Experienced participants agreed that 
the methods work better in areas with little variation compared with 
areas showing a complex pattern (many types of habitat). Used together 
with stratified sampling in different habitats, the method could provide 
good estimates of the total population size, but it is uncertain whether 
it could lead to a reliable estimate of densities in different habitats. 
Even the best searchers show a differential success in pellet finding in 
different habitats, but a correction can be established by scattering a 
known number of pellets in a plot and scoring the number of retrieved 
pellets. 
The identification of pellets is also more difficult than might be 
expected (in a known mixture of pellets of red and roe deer, 25% of the 
pellets were wrongly identified; so, test yourself). For statistical 
reasons the number of plots in each habitat must be at least eight, 
Irrespective of the relative area of that habitat type, but one should 
try to have at least 20 plots. Systematic sampling, which gives better 
covering of the area than a random sampling of plots, is not statisti­
cally inferior to the latter, but some of the participants still felt 
that a dung method to study habitat use only gives information about 
differential defaecation in the habitat types. This drawback could be 
overcome by calibrating the pellet counts against information on habitat 
use obtained by direct visual observation or telemetry, even though the 
telemetric results are biased too. This problem was not discussed 
further but is of paramount importance. It is felt that two sources of 
imperfect information can yield better results than one source (as 
suggested by e.g. Baeysian methods of interference). 
For comparison of the use of different habitats on the basis of the 
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dung method, it Is very Important to establish the smallest possible 
confidence limits for each estimate of dung density in the habitats in 
question. Although the decay rate of the dung is not important when the 
clearance method is used (i.e., all pellets removed from a plot after 
each count), this method is less reliable than the faecal standing-crop 
method (i.e., counting all pellets in a given area), because the latter 
method yields fewer zero values (theoretically this cannot be true). 
Zeros are extremely difficult to interpret, and for the analyses it must 
be assumed that the values from the different plots have a negative 
binomial distribution. 
Information from bite marks 
Since participants showed a general mistrust of indirect methods, it is 
hardly surprising that they voiced reservations about the use of bite 
marks for the study of habitat use, the quantification of foraging time, 
and the assessment of off-take. They were less doubtful with respect to 
woody species than about bite marks on grass or herbs. The main problem 
associated with bite marks is the difficulty of estimating the number of 
bites on herbs. One misses too many bites (but no one knows how many) to 
reach any quantitative conclusion about habitat use on the basis of 
scoring of bite marks. Even if one could score all bite marks on a sward 
and knew the total herbage mass, a 10% error in assessing the bite depth 
would lead to an error of +40% in bite weight and thus in forage 
offtake. This is rather depressing if you have worked 14 hours in the 
field to collect data of these types. Furthermore, certain food items 
completely escape notice with the bite mark technique, e.g. acorns. 
Assessment of food intake and diet composition 
Direct visual observation and telemetry 
During the present discussion this subject was only touched upon 
briefly. Estimation of bite size cannot be based on gravimetric quanti­
fication. The same applies to telemetry: the number of bites can be 
recorded via sensors attached to the jaw but an estimation of bite size 
is very difficult (Chapter VII). 
Faecal analysis: reliable information on the defaecation rate and the 
amount of faeces produced is difficult to obtain for wild animals 
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(Chapter VII). Faecal analysis has been used extensively for the 
assessment of the botanical diet composition, but bias with respect to 
the qualitative and quantitative composition should be checked by means 
of controlled experiments. 
Rumen analysis: rumen analysis is unreliable not only because of the 
differential passage rates of the particles of different sizes but also 
the different rates of digestion of plant species/plant parts. 
Bite marks: the tallying of bite marks was considered completely unre­
liable for grassy vegetation and herbs; it appeared to be more reliable 
for animals feeding on woody species. 
Exclosures and standing-crop assessment: during the discussion several 
participants repeatedly emphasized the point that both the food on offer 
and the offtake can be measured quite reliably by the use of temporary 
exclosures. This method was considered especially necessary for grassy 
vegetation or herbs. It must be kept in mind, however, that certain 
types of exclosure, particularly those using a cage, can induce an 
increase of primary production. This method is more suitable for esti­
mation of the offtake from a certain habitat type or location than for 
assessment of the animals intake, because most areas are heterogeneous. 
Assessment of food supply and grazing Impact 
Exclosures and standing-crop assessment 
Although this method was only touched on briefly, it appears to be the 
most reliable. Knowledge of phytomass on offer and food offtake in a 
given type of habitat or location and the animals' intake (per unit of 
time, per day) is essential if one wants to know why the animals are at 
a given place in the area at certain times. Information of this kind can 
only be obtained by the expenditure of much care and effort. 
Vegetation description and impact assessment based on bite marks 
This subject was not adequately discussed. The Braun-Blanquet method, as 
advocated by Petrak, makes use of a non-linear scale to weigh the impor­
tance of different plant species, and attaches too much weight to rare 
species. The method is apparently appropriate to describe plant species 
associations but is not adequate for estimation of the relative impor-
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tance of the amount of food offered by the Individual plant species. In 
this respect the point-quadrat method seems to be superior. The impact 
on vegetation was not adequately defined, but if it is taken as damage 
to e.g. trees as interpreted by foresters, Petrak's method could be of 
value. The problems would then be what foresters view as damage and the 
ecological meaning of their interpretation of bite marks. Petrak agreed 
that if interest is concentrated on biomass removal and its effect on 
the plants, use must be made of exclosures and harvesting techniques. 
Habitat description 
One of the major problems encountered in the study of habitat selection 
is how to understand a situation from the animal's angle. Many aspects 
must be taken into account here, not only the vegetation but also the 
degree of shelter, steepness of slope, height of shrubs, amount of 
timber, etc. Even cluster analysis of these data will not show how to 
weigh the various factors. When aspects and parameters are selected, the 
potential limiting factors for the animal should be considered and 
availability in the research area assessed. Factors such as available ad 
libitum level will have no influence. An attempt should be made to rank 
factors according to their relative importance and relative 
availability. Habitat classification - which must of course precede 
mapping for habitat-use studies - has proven to be very difficult. 
Perhaps the only satisfactory approach is to describe the habitat units 
in a very old-fashioned way, i.e., to use terminology to distinguish one 
'unit' from another (e.g., heathland, shrub, thicket, forest, meadow), 
and then use these units in the classification, mapping, and description 
of the habitat. But it is evident that this would give only a poor 
approximation of the animals' 'view' of the area. 
Incidental and unpredictable habitat characteristics can have a 
strong impact on habitat use, e.g., the presence of leaves or branches 
on the forest floor after a storm. 
Usefulness of the phenological calendar 
The participants agreed that the phenological calendar can be useful for 
the comparison of study sites within a large geographical area (e.g. 
Europe). The relevant data are often collected in botanical gardens 
belonging to the network of phenological stations in Europe. (The U.S.A. 
has a network of this kind too.) 


Habitat use of wild ungulates. Discussion.

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Habitat use of wild ungulates. Discussion.

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