Effect of Game Management on Wild Red-Legged Partridge Abundance
Vin uela J (2013) Effect of Game Management on Wild Red-Legged Partridge Abundance. PLoS
ONE 8(6): e66671. doi:10.1371/journal.pone.0066671
Effect of Game Management on Wild Red-Legged Partridge Abundance
Silvia Daz-Ferna ndez 0
Beatriz Arroyo 0
Fabia n Casas 0
Monica Martinez-Haro 0
Javier Vin uela 0
Nicola Saino, University of Milan, Italy
0 1 Instituto de Investigacio n en Recursos Cinege ticos , IREC (CSIC-UCLM-JCCM), Ciudad Real, Spain, 2 Estacio n Experimental de Zonas A ridas-CSIC , La Can ada de San Urbano , Almer a, Spain , 3 IMAR-Instituto do Mar, Department of Life Sciences, University of Coimbra , Coimbra , Portugal
The reduction of game and fish populations has increased investment in management practices. Hunting and fishing managers use several tools to maximize harvest. Managers need to know the impact their management has on wild populations. This issue is especially important to improve management efficacy and biodiversity conservation. We used questionnaires and field bird surveys in 48 hunting estates to assess whether red-legged partridge Alectoris rufa young/ adult ratio and summer abundance were related to the intensity of management (provision of supplementary food and water, predator control and releases of farm-bred partridges), harvest intensity or habitat in Central Spain. We hypothesized that partridge abundance would be higher where management practices were applied more intensively. Variation in young/ adult ratio among estates was best explained by habitat, year and some management practices. Density of feeders and water points had a positive relationship with this ratio, while the density of partridges released and magpies controlled were negatively related to it. The variables with greatest relative importance were feeders, releases and year. Variations in postbreeding red-legged partridge abundance among estates were best explained by habitat, year, the same management variables that influenced young/adult ratio, and harvest intensity. Harvest intensity was negatively related to partridge abundance. The other management variables had the same type of relationship with abundance as with young/adult ratio, except magpie control. Variables with greatest relative importance were habitat, feeders, water points, releases and harvest intensity. Our study suggests that management had an overall important effect on post-breeding partridge abundance. However, this effect varied among tools, as some had the desired effect (increase in partridge abundance), whereas others did not or even had a negative relationship (such as release of farm-reared birds) and can be thus considered inefficient or even detrimental. We advise reconsidering their use from both ecological and economical points of view.
Funding: This work was supported by the European Commission under the 7th Framework Programme for RTD through project HUNT (212160,
FP7-ENV-20071), the Consejera de Agricultura of JCCM through project Efecto del medio natural, las practicas agrcolas, ganaderas y de gestio n cinegetica sobre las
poblaciones de caza menor en los cotos pertenecientes a la Asociacio n de cotos de caza Sierra de Alcaraz-Campo de Montiel, and the Ministerio de Ciencia y
Tecnologa (CGL2008-04282/BOS). S. Daz-Fernandez had a predoctoral grant funded by the European Social Fund (ESF) and by JCCM (Operational Programme
PRINCET 2005-2010). F. Casas was supported by a JAE-Doc contract funded by the ESF. Currently, M. Martinez-Haro is supported by a postdoctoral grant (Ref:
SFRH/BPD/73890/2010) funded by the Portuguese Foundation for Science and Technology (FCT), the ESF and POPH programme. The funders had no role in study
design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
The collapse of commercial fisheries and large-scale population
declines of other harvested species are particular cases of the
current biodiversity crisis that should be dealt within a conceptual
framework integrating both ecological and social information ,
. Combining sound ecological knowledge of the harvested
species, as well as a proper assessment of the effect of human
actions to manage stocks, is essential to optimize long-term
exploitation of the harvested resources . Otherwise, incorrect
management programs may lead to resource depletion or
Hunting is practiced in many regions throughout the world
either for recreation or for subsistence, and it also has an
important economic dimension in many areas, sometimes
contributing importantly to rural economies , . A critical
management tool to maintain maximum sustainable harvest on
wild game populations is to adaptively adjust harvest through the
monitoring of game populations and the establishment of hunting
quotas in relation to their abundance , . However, robust
technical tools for adaptive decision making are scarcely developed
or applied yet , and management may not be always based on
scientific grounds . In fact, many wild game populations have
suffered severe declines in recent decades (e.g. ), mainly through
a combination of environmental factors (such as agriculture
intensification or climate change) and overexploitation or incorrect
Traditional hunting systems have been increasingly altered and
sometimes completely replaced by models based on more intensive
management. Management focused on increasing or maintaining
post-breeding game populations is thus carried out in many areas,
particularly when economic interests are strong , . The
most common management practices applied in Europe to
increase small game populations are predator control, habitat
management (increase of the quantity or quality of habitats used
by game species), species management (provision of supplementary
food or water, or medication to decrease parasites), or population
supplementation through releases of captive-reared animals .
Some of these hunting management practices are controversial
and may lead to conflicts between stakeholder groups. For
example, predator control has a strong negative connotation for
many non-hunters  and has been associated in cases to
detrimental effects to protected predator populations  (and
references therein). On the other hand, this technique is frequently
considered by hunting managers as necessary to maintain hunting,
or at least the economic profitability of this activity, and it may also
help population recovery of non-target protected species ,
. Similarly, the use of restocking to increase small game bags
has been criticized because of its negative effects on wild game
, but it may strongly increase hunting yield and economic
output of hunting estates in certain cases .
Several studies have shown that game management is usually
related to higher abundances of target game species (e.g. ,
). This makes it easy to intuitively assume that the pool of
management actions applied is useful to increase abundances, but
few studies have evaluated the relative efficacy of each practice
when applied simultaneously. Such an assessment would help in
cost-benefit analyses of different management scenarios to reduce
controversies and, ultimately, be able to optimise management
decisions for game, biodiversity and society at large.
In Spain, the red-legged partridge Alectoris rufa L. is one of the
most important small game species numerically and economically
, . Its importance as a source of economic activity has even
grown in recent decades as part of the general Spanish hunting
"boom , despite its well recorded, large-scale and deep
population decline in the second half of the XXth century .
Hunting estates are increasingly managed with costly and
specialized techniques . Red-legged partridges are generally
more abundant in areas of extensive farmland with high density of
edges and a mixture of natural vegetation , . Availability
of water points influences red-legged partridge distribution ,
but their effect on abundance has not been tested, and there exist
few studies about the effects of supplementary food provisioning
, a very commonly used tool , . Predator control, also
widely used, is known to be effective to increase game numbers
when performed intensively , , although no studies have
been done specifically in Spain where the network of predators
(protected and unprotected) is rich and diverse, and their effect on
prey populations scarcely known . Finally, negative effects of
restocking on wild red-legged partridge populations such as disease
spread, changes in population genetic pool or overhunting have
been found , , whereas the effectiveness of small-scale
releases to increase hunting yields has been questioned .
The intense use and demand of red-legged partridge in Spain
, and the large geographical spread in management aimed to
raise the harvestable stock , makes it critical to assess the
efficacy and consequences of the management activities to discuss
the best management options to maximise long-term economic
profitability of the hunting activity and secure conservation of the
game species, promoting management favouring ecosystem
conservation while minimising the use of techniques that may be
We studied the relationship between post-breeding partridge
abundance (i.e. the huntable stock) and the intensity of various
management tools currently applied in hunting estates (food and
water supplementation, predator control and restocking), whilst
also taking into account two other variables that are known or
expected to affect game densities (habitat and harvest levels). We
hypothesized that partridge abundance would be higher where
management practices were applied more intensively, but we were
particularly interested in knowing which contributed more to
increase abundance, if applied simultaneously. We discuss our
results in terms of their application to improve sustainable
exploitation and conservation of a socio-economically important
game species with declining wild populations.
Materials and Methods
We studied 48 hunting estates located in Central Spain, in
latitudes ranging from 37.98N to 40.33N and longitudes from
6.48W to 2.11W, ED 1950 (see  for a figure). The dominant
open landscapes of these estates were characterized by different
proportions of cultivated land and natural vegetation (mainly
Mediterranean scrub, Table 1). Estate size ranged from 2 to 280
km2 (mean6SD = 36.79654.70; sum of all estates 1765.95 km2).
Land was mostly privately owned and censuses were carried out
with the approval of the person responsible of the game activity
within the estate.
Game management in the studied estates was mainly aimed to
red-legged partridge hunting. We selected privately managed
estates, which are the great majority in the region (87% ),
either with commercial or non-commercial goals, but excluding
intensive estates (those with license to release farm-bred partridges
without numerical limits throughout the hunting season).
Management in intensive estates is qualitatively different from that in
other types of estates, and harvest there depends directly on the
number of partridges released but not on wild red-legged partridge
populations , . Studied estates varied largely in the
intensity of management performed (as seen in the large SD of
means in Table 1, see also ).
Partridge abundance data
We estimated partridge abundance from field observations in
each hunting estate, using a point count method . Observers
drove along tracks distributed throughout the whole of the estate
or, when it was too big, a representative area of the estate
stratifying by habitat. Every 700750 m (exact point depending on
visibility of the surrounding area) observers stopped, and partridge
numbers and locations were recorded during 10 minutes, using
binoculars. Observations took place on early morning (from
sunrise to ca. 3 hours later) and in the evenings (34 last hours of
the day), avoiding the hottest central hours when partridge activity
is lowest. Observations were also suspended in case of rain or too
windy conditions. Distances from partridges to observer were
estimated visually with a precision of 50 m. The number of
observation points in each estate was 55670 (range: 4425,
depending on estate size).
From this information, we calculated a summer partridge
abundance index (hereafter partridge abundance) as the sum of
recorded partridges within a radius of 300 m at each observation
point, divided by the number of observation points monitored in
each estate. We selected this simple abundance index instead of
e.g. estimating densities from distance sampling, because we were
mainly interested in relative abundance estimates that were robust
enough to be comparable among hunting estates. Distance
sampling estimates need a minimum of observations to reliably
estimate detection functions , so they lose reliability when
abundance is low, as is the case of some of our estates.
Additionally, preliminary analyses showed that detection functions
mainly depended on observer, as there were significant differences
among observers in the estimated distances of observation,
particularly in the smaller ranges, whereas there was wide
agreement among observers on separating whether observations
were within 300 m or beyond. In any case, there was a very good
We recorded habitat data during bird surveys as the percentage
of each habitat type within a radius of 100 m at each observation
point, and then calculated habitat for each estate as the average for
all surveyed points. We considered the following habitat variables,
defined with functional and management meaning for red-legged
partridge , : arable land (mostly cultivated with winter
cereal or left in annual fallow, the latter usually ploughed during
summer; secondarily cultivated with other annual crops),
vineyards, tree crops (mainly olive groves, secondarily almond trees,
occasionally fig trees), uncultivated grasslands (including old fallow
land and uncultivated areas covered by low herbaceous
vegetation), Mediterranean scrub (mainly medium-height Mediterranean
scrubs, most often Cistus sp., Halimium sp., Retama sphaerocarpa,
Mediterranean scrub (%)
Uncultivated grasslands (%)
Estate scale Shannon index
Point scale Simpson index
Summer red-legged partridge abundance (partridges/survey point)
Big water points (big water points/km2)
Small water points (small water points/km2)
Foxes controlled (foxes controlled/yr/km2)
Magpies controlled (magpies controlled/yr/km2)
Partridges released (partridges/km2)
concordance between density estimates based in distance sampling
and our abundance estimates based in point counts in estates for
which we could estimate densities based on detection functions
(r2 = 76%, n = 33).
Additionally, we calculated for each estate the ratio of young to
adult partridges observed (hereafter young/adult ratio), when
information about partridge age was available (n = 37 estates, in
which the proportion of observations of non-aged partridges was
lower than 25%). Young/adult ratios can increase with increased
young production or with increased adult mortality. Thus, it
cannot be considered as directly equivalent to partridge
productivity (i.e. the number of young produced by each pair). However,
we considered this ratio as indicative of productivity for the goal of
this study, as young mortality is much higher than adult mortality
during summer months , so it seems reasonable to assume that
high young/adult ratios mainly reflects young production, rather
than high adult mortality. Indeed, our data show that total
abundance was positively related to larger young/adult ratios
within the sample, supporting this (Fig. 1).
Fieldwork was carried out from mid June to early August,
during the red-legged partridge chick rearing period . Specific
survey dates of each estate were selected to coincide with the time
when most of the cereal had been harvested, in order to maximize
visibility, but before farm-bred partridge releases occurred (if they
happened at all). In non-intensive estates, releases usually take
place as close as possible to the hunting season, i.e., from August to
September. From the sample of 48 estates, we excluded from
analyses four of those as we had strong suspicions of possible
summer releases not reported in the inquiries (high summer
abundance with very low young/adult ratio, Fig. 1; and
out-ofrange annual harvest, see ). Surveys were carried out from
June 16th to July 31st in 2006 (n = 25) and from June 16th to
August 12th in 2009 (n = 19).
Rosmarinus officinalis, with a strong component of Quercus coccifera
and holm oak Quercus ilex, the latter sometimes achieving full tree
height), woodland (pine or eucalyptus plantations, secondarily
poplars), or dehesa (areas of sparse oak woodland which may be
cultivated or grazed underneath). We also calculated habitat
Shannon diversity index for each estate from the mean percentage
for every habitat category in the estate, and Simpson diversity
index  as the average of Simpson indexes calculated for each
observation point separately. Simpson index is equivalent to the
probability that two randomly selected points correspond to the
same habitat (maximum diversity if index is cero) and was an
indicator of spatial variability in habitat.
Management and hunting data
We collected management data through face-to-face
questionnaires with game managers that voluntarily participated in the
study. For each estate, we obtained data on estate size, number of
feeders (devices with grain or commercial feed to be consumed by
partridges, refilled always during spring and summer, sometimes
also in winter), number of artificial water points (see below),
number of foxes and magpies annually killed (the two most
important predators legally controlled in the area), number of
farm-bred partridges annually released and red-legged partridge
annual harvest (i.e. number bagged). These data usually
corresponded to the hunting season previous to the measure of summer
abundances. All variables were expressed per estate surface for
Artificial water points were of two types: small and large. Small
water points, which contain less than 500 l, are water tanks
maintaining a constant water level in an external small dish. Large
water points are shallow artificial ponds containing more than 500
l of water and covering up more than 100 m2. We found that the
number of small water points and the number of feeders were
highly correlated in the estates (Pearson = 0.87, see Table S1 in
Supporting Information), as they are usually placed together.
Thus, one of them retains information for both, and we only used
the density of artificial feeders in subsequent analyses. Other
management variables were not strongly correlated among them
We also obtained an estimate of hunting intensity as the
residuals of the linear general model with number of partridges
harvested as response variable and partridge abundance as
explanatory variable. Our values for number of partridges
harvested corresponded to the hunting season previous to the
field survey. Between-estate variability in harvest was higher than
among-year variability for a given estate, and thus our data
represent an adequate estimate of annual harvest for each estate
We lacked data on harvest (and thus hunting intensity) for four
of the estates (two of which also lacked information on fox and
magpie numbers killed). Two further estates also lacked
information on the number of magpies killed. Given that comparisons of
AIC between different models are only possible if the same sample
is used in all models , we eliminated these data for Generalized
Linear Models (GLM) analyses. We also carried out analyses with
the full (n = 44) sample, replacing missing values for average values
from the whole sample. Variables included in the selected models
were similar with both data sets, so we present results for the
smaller one (more conservative and robust).
Following current legislation and ethical rules for human
research in Spain, data from questionnaires used in this work
does not need approval from an ethics committee, as the data
gathered are not related to biological or medical human data ,
and do not correspond to indentified individuals or individuals
possible to be identified . In fact, they do not correspond to
individuals, but to hunting estates, which are not within the
current data protection law . We have consulted the Ethics
Committee on Human Research of the University of Castilla La
Mancha, which consider that the evaluation of such proposal is not
within their competence, supporting the statement above.
Analyses were carried out with R 2.13 .
We wanted to evaluate which management variables explain
summer red-legged partridge abundance while removing the
expected effect of other variables (such as habitat). Therefore, we
carried out analyses in two steps. First, we tested certain models
including habitat variables, based on prior information about
habitat needs for the species , , . At a broad scale,
redlegged partridges are known to be more abundant where arable
land is the main land use , . However, at a smaller scale,
highest abundances have been found in those estates with arable
land mixed with Mediterranean scrubland, particularly in those
with large proportions of both of those habitats  , and in
areas with high farmland habitat diversity . According to this,
models we tested included: habitat diversity, and arable land
mixed with Mediterranean scrub. These two latter variables were
also those that covered on average more than 20% of the surface,
and which could attain more than 80% in certain estates (Table 1).
We also evaluated whether quadratic variables should also be
included, as an optimum of any variable is expected if the ideal
landscape includes combinations of both of them. However, no
variable fitted a second order polynomial when tested in bi-variate
curve-fit analyses (results not presented), so we did not include
them. Additionally, as censuses were carried out in two different
years, we included year as an additional potential variable in all
the above models, to account for potential among-year variations
in abundance not related to management (Table 2). We evaluated
which of those models best explained variations in abundance,
according to AICc values. Variables in the selected model were
subsequently combined with all management variables. We
performed all possible combinations of these independent
variables, as all of those models were biologically plausible and
we were interested in whether each game management variable
alone or in combination with others or with habitat variables could
explain partridge abundance variation among estates. We did this
with the function dredge (library MuMIn), selected the models
with delta AICc ,2, and calculated model-averaged parameter
estimates for the variables included in those models, as well as their
relative importance, calculated as sum of Akaike weights across all
the models in the set where that variable occurred .
An initial exploration of data showed that abundance was
positively correlated with young/adult ratio (see results). We
evaluated the effect of management variables, the selected habitat
variables (Table 2) and year on abundance (using a data set with
n = 38 estates for which information on all management variables
existed). Additionally, we evaluated the effect of management
variables, the selected habitat variables (Table 2) and year on
young/adult ratio (using a data set of n = 28 estates for which
information on both young/adult ratio and all management
variables existed). We assumed that variables affecting abundance
that were not included in the model explaining young/adult ratio
were variables mostly affecting density of breeders.
Factors affecting variation in response variables (abundance or
young/adult ratio) were analysed using GLMs. We fitted response
variables to a Gaussian distribution. In all models, we included the
D-W: Durbin-Watson statistic.
a: arable land; ms: Mediterranean scrub; yr: year; simpson: simpons index of
habitat diversity; shannon: shannons index of habitat diversity.
variable number of count points divided by estate area as a
weight, to control for the potential effect of bird census intensity on
the abundance estimate. We checked for normality of residuals of
the final models. In those, we also calculated the variance inflation
factor (VIF, ) with the function vif (library HH), considering
that a VIF ,2 indicates a lack of collinearity among variables
within the model ; and the Durbin-Watson statistic with the
function dwt (library car) to check for autocorrelation of residuals
Summer red-legged partridge abundance was linearly and
positively related to young/adult ratio in our sample of hunting
estates (n = 33), the latter explaining 65% of the variance in
summer abundance (Fig. 1).
Of all models tested to explain temporal and habitat variations
in partridge abundance, the best model included Mediterranean
scrub and arable land. Within delta AICc values ,2 were also
those models including year, or estimates of landscape diversity.
However, the combinations of arable land, Mediterranean scrub,
landscape diversity and year were much worse (in terms of AICc
values) (Table 3). Of the best models (those with delta AICc values
,2), we thus chose the one including year, arable land and
Mediterranean scrub as the one more biologically meaningful
among the equivalent ones.
Best models explaining variations in partridge young/adult ratio
included one habitat variable (Mediterranean scrub), year (with
higher young/adult ratio observed the second than the first study
year), and several management variables: the density of feeders,
big water points, intensity of release of farm-reared birds, harvest
intensity and magpie control intensity (Table 3). Density of feeders
and big water points had a positive relationship with young/adult
ratio, while the density of partridges released, harvest intensity or
magpies controlled were negatively related to young/adult ratio
(Table 4). The parameter estimate of magpies controlled included
0 if taking into account the standard deviation. Of all of these
variables, the ones with higher relative importance were feeders
and releases (Table 4).
Best models explaining variations in summer partridge
abundance included the same variables explaining partridge young/
adult ratio except magpie control intensity, which was substituted
by fox control intensity (Table 3). Feeders, water points, harvest
intensity, releases and Mediterranean scrub had all the same type
of relationship with abundance as with young/adult ratio, and had
also high relative importance (Table 4). Year had a negative
relationship with abundance (higher abundance observed in the
first study year). Fox control intensity was negatively related to
abundance, but had a very low relative importance and its
parameter estimate also had a large standard deviation related to
the mean (Table 4).
We did not detect problems of autocorrelation of residuals
in any of the final best models selected (Durbin-Watson statistic
= ,2, presented in Table 2). VIF for the variables in the selected
best models was between 1.00 and 1.61 and thus, we did not find
problems of collinearity in these models.
Our study shows that management and habitat have a strong
effect in explaining post-breeding abundances. However, this
effect varied among management tools, some of them having a
positive effect on abundance, others having undetectable or even
detrimental effects. These results allow building an open decision
framework for managers, which could be applied to optimise both
economic objectives and wild game sustainability. We discuss these
Factors affecting partridge abundance
We found an important effect of year on partridge young/adult
ratio or abundance, although the relationship was opposite in both
variables. Previous studies have highlighted the strong influence of
climatic conditions on red-legged partridge young/adult ratio
, , , so observed variations may be related to weather
conditions affecting differentially young or adult survival.
Both young/adult ratio and total abundance were positively
related to the provision of supplementary food or water, and to the
availability of Mediterranean scrub, but negatively to releases of
farm-reared partridges or to harvest intensity.
Habitat-related factors are considered crucial to determine the
distribution and density of the populations of most species ,
including red-legged partridges. In our study, post-breeding
abundance and young/adult ratio were higher in those estates
with higher proportion of Mediterranean scrub, which coincides
with other studies that suggest that a mixture of scrub and agrarian
habitat is an optimal habitat for this species , . Overall,
habitat was less important than management to explain young/
adult ratio. It is possible that some characteristics of farmland
management not included here have important influence on
partridge young/adult ratio , . For example,  found
that field edges in agricultural landscapes or the timing of cereal
harvest were crucial for successful breeding. Similarly,  found
a high spatial association between brood sizes and field edge
density and natural vegetation. Our sample size was not large
enough to test for interactions between habitat and other
management variables, but it could be envisioned that the effect
of food supplementation is larger in those habitats with lower
proportion of natural food, or that the effect of predator control is
only noticeable in degraded farmland habitats, where protective
habitat is scarcer. Further studies should clarify this and consider
the inclusion of other agricultural management variables, which
may improve the value of habitat models in explaining variations
in partridge abundance.
In terms of management techniques, we found that provision of
supplementary food was the management variable with the
strongest positive effect on young/adult ratio (and thus
postk: number of parameters. D-W: Durbin-Watson statistic.
a: arable land; ms: Mediterranean scrub; f: feeders; w: water points; r: releases; hi: harvest intensity; mg: magpie control intensity; fx: fox control intensity; yr: year.
breeding abundance). The provision of food and water has been
frequently suggested for gamebird population improvement ,
,  and is commonly used for red-legged partridges .
However, its efficacy has been sometimes contested . In fact, it
has also been suggested that food and water supplementation
could be unnecessary  or even have negative consequences,
because feeders and water points could enhance disease
transmission through higher contact between individuals , , and
could also enhance attraction of predators and poachers . Our
results support a positive relationship between food
supplementation and red-legged partridge abundance and young/adult ratio,
suggesting that food may be limiting in our managed areas. As
stated above, if this was the case we should expect interactions
between habitat and the influence of feeder density, which would
be interesting to test in future studies. Alternatively, and since the
density of feeders was correlated to the density of water points, the
effect of feeders could be indicating the beneficial effect of water
provision, which is also evidenced in the positive effect of provision
of big water points.
Positive effects of water availability on survival or population
dynamics have been found in other Mediterranean galliformes
. Red-legged partridges use water points usually during
summer, especially under harsh climatic conditions , and
spatial distribution in summer is influenced by presence of water
troughs . An alternative explanation to the positive
relationship between provision of water troughs and density could be that
partridges find other important resources around water points,
such as green vegetation, insects or cover. One way or other, our
results support that water supplementation in Mediterranean
habitats is a beneficial management tool for red-legged partridges,
despite this species being well adapted to scarcity of water.
Importantly, partridge young/adult ratio (and thus summer
abundance) decreased with increasing numbers of farm-reared
partridges released. It may be argued that more partridges are
released in areas with poor productivities, but in any case, what is
clear from our results is that releases are not effectively increasing
summer abundances. It may also be argued that the main goal of
releases is just to increase partridge bags in the short term and not
to increase summer abundance, and thus effectiveness may not be
measured in terms of summer abundance. Indeed, harvest
intensity had also a negative strong effect on partridge young/
adult ratio and summer abundance. At a larger scale, an increase
in hunting pressure has also been found to have a significant effect
on the population decline observed in Spain since 1970 . This
also suggests that a careful adjustment between take and
abundance is critical for population sustainability in this game
species. Moreover,  showed that releases in low densities are
not effective to increase harvest either. Both findings lead to the
conclusion that farm-partridge releases in small densities are at
best ineffective to increase red-legged partridge hunting bags in the
short (annual) or medium term in private hunting estates in
Central Spain, as has been previously suggested , which could
increasing the likelihood of overhunting of wild populations .
Otherwise, other studies suggest that releases are indeed negatively
affecting the viability of wild populations, through spreading
parasites or diseases , , or modifying the gene pool
through the presence of breeding hybrids between A. rufa and A.
chukar in wild populations, due to lack of genetic control of released
Finally, it is interesting that we did not find an important effect
of predator control intensity on partridge summer abundance or
young/adult ratio. We found negative relationships between
magpie control and young/adult ratio or fox control and
abundance, but these variables had a relative low importance
compared with other factors, and the parameter estimates had
large standard deviations (including zero at least in the case of
magpie control). This agrees with the concerns of  about the
lack of effect that predator control could have in real-life
management situations, contrasted to the effectiveness of very
intensive control found in experimental situations , . An
alternative explanation is that predator control effectiveness
interacts with other variables, such as habitat type. One of the
limitations of our study (which, in any case, reflects also the
limitations of the managers themselves) is that we did not evaluate
predator abundance, and hence it is not possible to evaluate the
effectiveness of predator control on reducing predator abundance
in each of the studied estates, which may explain the observed
results. However,  did not find a relationship between red fox
abundance and predation frequency or summer partridge
abundance, so our results may indicate that partridges are able
to cope with the levels of predation experienced, or that different
predators interact preventing effects to be detected. On the other
hand, we found positive relationships between the intensity of fox
control and the abundance of another farmland bird, the little
bustard Tetrax tetrax (authors, unpublished data), which suggests
that our measured variable has indeed a biological meaning (i.e.,
that higher levels of predator control are indeed associated to
lower predator numbers). Considering the widespread use of
predator control in Central Spain (85.2% of small game estates in
Castilla-La Mancha ), its low effectiveness for partridges, its
possible negative effects for protected predators  (and
references therein), and its possible positive effects for other
protected species , , a cost-benefit evaluation in different
contexts may help to optimize benefits in relation to this
management tool. Further studies should concentrate in these
Implications for decision making in managers
Decision making in conservation and management is frequently
done under a great degree of uncertainty, and with multiple
objectives (economic, ecologic and social). Managers frequently
have to face trade-offs or dilemmas about how and where to invest
in management, which tool to promote or in which circumstances.
In many cases, these decisions are taken subjectively, or based on
general assumptions. In some cases, investment is made in all
potential management tools (like is the case of red-legged
partridges), without a real evaluation of the relative costs and
benefits of each individual tool.
Our results provide critical information to help managers in
their decision making, and could be used, if coupled with an
evaluation of the economic cost of each tool, to build an open
decision framework for managers, which could be applied to
optimise both economic objectives and wild game sustainability.
In the case of red-legged partridges in Central Spain, our results
indicate that the best strategy to reinforce wild populations would
be to concentrate in improving food and water availability, either
directly through providing supplementary food and water (as
currently done) or indirectly through improving habitat quality,
which could be expected to be a more efficient, stable and
profitable long-term strategy , , . In that sense,
measures such as maintaining the right percentage of scrub
habitats or keeping a proper density of field edges within the
agrarian landscapes, would be also a basic measure to increase
red-legged partridge abundances, and thus the availability of this
singular renewable resource. On the other hand, investing in
small-scale re-stocking with farm-bred partridges is inefficient,
potentially detrimental, and should be thus limited in most
circumstances (both on economic and ecological arguments).
Thus, the management panacea of releasing farm-bred birds
does not seem to be efficient or secure enough to justify its
expanding use as a replacement of correct wildlife resource
management, as has been suggested for recreational fisheries too
More generally, our results indicate that some game
management practices are more efficient than others, and that their joint
application may not lead to additive results. Studies identifying the
relative importance of individual management tools when applied
simultaneously may thus help evaluating the relative economic and
conservation value of different managerial scenarios.
We thank A. Arredondo, B. Campos, J. Caro, M. Casado, F. Daz, J.
Duarte, I. Garca, E. Garca, J.L. Guzman, J. Lopez-Jamar, C.A. Martn,
E. Osorio, X. Pi neiro, T. Polo, J. Sanchez and M.J. Valencia for their help
with fieldwork; game managers for their collaboration; the Asociacion de
cotos de caza menor Sierra de Alcaraz-Campo de Montiel for facilitating
collaboration with game managers, M. Delibes-Mateos for coordinating
bird census in 2009, again M. Delibes-Mateos and N. Bunnefeld for useful
comments on the initial draft of this manuscript, and A. Meriggi for useful
comments during the final revision this manuscript.
Conceived and designed the experiments: SDF BA JV. Analyzed the data:
SDF BA. Contributed reagents/materials/analysis tools: BA JV. Wrote the
paper: SDF BA FC MMH JV. Conducted some of the partridge censusses:
FC JV MMH. Conducted face-to-face questionnaires: SDF.
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