BACKGROUND
communities are shaped by interspecific interactions and specific adaptations, depending on the nature of the interaction , allowing coexistence  <cit> .
effects of competition might be masked by behavioural adaptations as a result of a shared evolutionary history.
studies of interspecific competition have mainly focused on how indirect exploitation competition affect behaviour, e.g., via territoriality and foraging strategy  <cit> , and have neglected the implications of direct interference for community structure  <cit>  and evolution  <cit> .
direct antagonistic interactions in competition for food, space, nest sites, or mating partners can be very costly, especially if the competition reduces individual fitness   <cit> .
aggressive behavioural confrontations between competing species are likely if adults prey on each others offspring  <cit> .
interference may result from resource-related aggression between heterospecific or conspecific individuals with potential effects on niche use and community structure   <cit> .
nest predation has been considered a special case of direct interference via interspecific killing  <cit> .
it is a significant source of offspring mortality and can strongly affect parental life history strategies  <cit> .
although numerous population studies have shown that nest predation is widespread in animal communities  <cit> , its importance as an evolutionary force has been neglected  <cit> .
recent studies on avian breeding biology demonstrate that the direct fitness effects of nest predation can drive evolution  <cit> .
safety of nest sites and optimised breeding conditions are key intrinsic components of breeding habitat quality  <cit> .
adults should adapt their behaviour to predation risk  <cit>  by, e.g., choosing concealed nest sites  <cit> , adjusting clutch size or nestling period  <cit> , and temporally partitioning foraging activity  <cit> .
comprehensive knowledge about adaptive strategies against nest predation in mammals is lacking.
yet defence of a nest and its vulnerable young is a powerful explanation for the ultimate function of female aggression and territoriality, which is most intense during lactation and near the nest site  <cit> .
in addition, nests  or burrows  serve as micro-refuges from predators and therefore have anti-predatory benefits for the adult as well  <cit> .
parental anti-nest predatory behaviour
according to parental investment theory, parents must trade off the benefits of investment into current offspring with possible negative effects on their future inclusive fitness  <cit> .
in addition, parents might suffer extra costs of defending offspring against predators, including time, energy, and missed opportunity costs  <cit> .
short-term adjustments are often trade-offs between behaviours, e.g., predator avoidance and foraging  <cit> , and escalate in defending offspring against predators or infanticidal conspecifics  <cit> .
the degree of escalation is influenced by offspring vulnerability and reproductive value to the parent  <cit> .
female rodents become more aggressive during their pregnancy  <cit> .
female european rabbits  increase vigilance during late pregnancy to minimise predation  <cit> .
in mice, mothers successfully defend their nestling pups against infanticidal conspecifics  <cit> .
attacks on pups decrease rapidly after they reach a less vulnerable stage  <cit> .
maternal defence behaviour against rattlesnakes declines in california ground squirrels as snake activity declines when pups grow older  <cit> .
according to the “harm to offspring hypothesis” of dale et al.
<cit> , the level of parental predation risk-taking is adjusted according to the harm the offspring will suffer without parental care.
most vulnerable are altricial nestlings incapable of escaping and defending themselves  <cit> .
predation risk is highest when the parents are away   <cit> .
in response, parents might alter their foraging time  or seek temporal or spatial foraging refuges to decrease risk  <cit> .
cresswell  <cit>  showed that nesting blackbirds altered their nest defence behaviour to compensate for predation risk demonstrating that parental behavioural flexibility in response to predation can yield fitness benefits  <cit>  compared with fixed strategies  <cit> .
for semi-fossorial mammals, the morphology and complexity of burrows have high defence value for nestlings and thereby fulfil an anti-predator function, especially for animals with helpless altricial young  <cit> .
hunting intruders might be confused by very complex burrow systems  <cit> .
some species dig special parturition chambers in addition to the main burrow  and plug them to minimise predation .
increased vigilance  at burrow entrances and adjusting burrow attributes  may further lower the risk of nest predation  <cit> .
physiological stress responses to nest predation risk
physiological responses in stressful situations, e.g., encounters of prey with predators, are evolutionarily conserved and represent a widespread and fundamental mechanism for ecosystem functioning in animal systems  <cit> .
predator-induced changes in stress hormone metabolites associated with acute or chronic risks  aim to increase survival  <cit> .
animals without adequate alternative defence responses  to mitigate predation risk must engage in costly physiological responses  <cit> .
elevated plasma glucocorticoids, or their faecal metabolites, are often measured as indicators of such physiological stress responses  <cit> .
study system and hypotheses
here we compare behavioural strategies among different interaction types: interspecific resource competition, intraspecific interference competition, and interspecific nest predation.
we used a small mammal study system including the semi-fossorial common voles  as focus animals, the greater white-toothed shrews  as potential nest predators, and field voles  as interspecific competitors.
all three species coexist in many habitats of the northern hemisphere, overlapping in their common habitat and, to a smaller extent, in their diets  <cit> .
voles live in large burrow systems with underground tunnels and corresponding runway systems above ground.
shrews explore vole tunnel systems to search for invertebrate food  <cit> .
because of the limited space underground, shrews may react aggressively when encountering tunnel inhabitants.
additionally, they can act as nest predators on altricial vole nestlings by plundering their easily accessible nest chambers  <cit> .
this shrew behaviour might intensify during environmentally-adverse seasons when invertebrate food is scarce, e.g., in autumn  <cit> .
to protect vulnerable altricial nestlings from nest predators, voles should have evolved anti-nest predator strategies to secure their reproductive success.
getz et al.
<cit>  reported nest defences in two american vole species, microtus pennsylvanicus and m. ochrogaster, even against larger shrew species, e.g., blarina brevicauda.
shrews only successfully preyed on nests when vole mothers were absent on foraging trips  <cit> .
what kinds of parental behavioural strategies can secure nestling survival and allow the coexistence of competing species in a nest predator–prey system?
how do these strategies differ from responses to non-nest predator antagonists?
we hypothesised that vole mothers adjust their burrow systems in response to antagonists  <cit> .
if she encounters a nest predator during pregnancy, we expected to find different nest architectures at parturition than in the absence of predators.
we further hypothesised that vole mothers react to nest predation risk by altering their time budgets and habitat use.
to guard vulnerable nestlings, vole mothers should increase vigilance and nest guarding behaviour , especially during the first sensitive nestling phase.
we expected guarding behaviour to be more intense in the presence of a potential nest predator than in the presence of an inter- or intraspecific resource competitor.
in addition, if guarding behaviour incurs extra costs for vole mothers, e.g., owing to shortened foraging periods, we expected that to be reflected in the mother’s or nestlings’ body conditions.
if vole mothers exhibit physiological stress reactions concomitant to these behavioural reactions , we expected levels of faecal corticosterone metabolites  to correlate to the presence or absence of different antagonists.
thus, we hypothesised that the levels of stress hormone metabolites in expectant vole mothers increased when they encountered shrews as nest predators.
RESULTS
behavioural adaptations: burrow architecture
the numbers of burrow entrances built by vole mothers were significantly influenced by the type of antagonist .
in the np treatment, they built fewer entrances  compared with the rc  or c  treatments.
the depth of the nest site was also influenced by antagonist type .
mothers built nests closer to the surface in the np  than in the rc  or c  treatments.
behavioural adaptations: activity in burrow entrances
the treatment species had a significant effect on the mothers’ activity in the burrow entrances .
vole mothers in the np treatment spent more time in entrances  compared with those in the rc  or c  treatments .
the mean number of readings/bout  and the mean number of seconds vole mothers spent in entrances per bout  were not influenced by the antagonist species.
we also recorded all treatment species entering the tunnel entrances .
seventy-eight per cent of the shrews  entered the burrow systems, while only 50% of the field voles  and 43% of common voles  did so, but the latter two species visited the burrow system more often per replicate than did the shrews .
the number of antagonist visits to the vole burrow was recorded using automatic transponder-reading antennas inserted into tunnel entrances.
stress hormone level
we found no difference in the baseline amount of fcms before the treatments .
under treatment conditions , fcms were affected by an interaction of treatment and sampling .
mothers in np treatments had a higher fcm levels around parturition  compared with the other treatments  and compared with the postpartum period  .
the fcm of vole mothers did not differ any more between treatments when nestlings were  <dig> d old .
non-significant post hoc results are not displayed.
maternal body condition and offspring survival
we found no influence of treatment on the vole mother’s body weight , either prepartum  nor postpartum .
we also found no influence of antagonist species on offspring survival .
both the number of vole nestlings  and nestling body weight  were independent of antagonist species.
discussion
we investigated behavioural and physiological responses of vole mothers to different intra-nest interactions: nest predation, interspecific resource competition, and intraspecific competition.
nest predators affected burrowing behaviour and passage activity at burrow entrances as well as physiological stress responses.
the presence of neither a potential nest predator nor a competitor species altered reproductive success.
furthermore, nestlings in all treatments were in good condition.
these results indicate that vole mothers seem to perceive shrews as a threat and adequately respond to their presence.
treatment animals of all antagonist species visited the vole mothers’ burrow system several times.
vole mothers were apparently successful in defending their nestlings against potential nest predation attempts.
adaptive anti-nest predatory strategies
pregnant common voles responded to the presence of a potential nest predator or a resource competitor with different nest site preparations.
contrary to findings on african gerbil  and prairie vole  mothers, which build complex burrow systems to confuse predators or to hide nestlings  <cit> , the common voles in our study constructed simpler burrow systems in the presence of nest predators, but not when a competitor species was present.
nest defence might be more efficient in a basic burrow system than in a complex one.
additionally, simpler refuges might help to reduce interactions with antagonists and avoid unnecessary energetic costs  <cit> , as in complex tunnel systems.
another explanation might be that pregnant females without nest predation pressure stayed in their prepartum burrow, while pregnant females threatened with a nest predator may have dug a new, isolated nest site  <cit> , as shown in laboratory rats  <cit>  and european rabbits  <cit> .
by preparing the nest site prepartum , mothers might try to avoid spending energy postpartum in digging and guarding the nestlings.
these findings agree with the “harm to offspring” hypothesis  <cit> , which predicts that mothers should minimise periods of vulnerability during parental absence   <cit> .
common vole burrow traits in the presence of a heterospecific competitor might reflect a general necessity for nestling protection against possible intruders.
harper and batzli  <cit>  found no strong effect on the burrowing behaviour of prairie voles by the presence of heterospecific meadow voles.
although heterospecific resource-related aggression can have similar consequences to predation effects   <cit> , vole mothers seemed to differentiate between the risks of heterospecific aggression and nest predation.
nest guarding and vigilance behaviour as indicators of the perceived predation risk suggest that vole mothers have adapted to shrews as nest predators through a shared evolutionary past.
only in the presence of shrews did vole mothers spent long time periods in the burrow entrances.
increase of vigilance is a common response to predator odour  <cit> .
for example, female european rabbits increased their vigilance , especially during late pregnancy, to deter attacks by potential predators  <cit> .
female mammals must allocate their time among maternal care, foraging, and vigilance, especially during the first days of nestling life.
in some species, this trade-off adversely affects the condition of pregnant or lactating females  <cit> .
we found no effect of increased vigilance in the shrew treatment on neither maternal nor nestling body weight.
other studies with simulated predation risks also demonstrated stable food intake, despite increased vigilance  <cit> .
vigilance and foraging during the energetically-demanding reproductive phase are therefore not mutually exclusive, and mothers in our experiment were able to successfully protect their young against nest predators without suffering energetic costs.
this finding might not apply under natural conditions, e.g., if food for shrews is scarce and shrews exert higher predation pressure on vole nestlings.
physiological stress responses to nest predation
the physiological stress response to the presence of a nest predator during late pregnancy was higher than in other competitor treatments or in the postpartum phase.
a few days after parturition, the levels of fcms decreased almost to pre-treatment baseline levels.
female rodents were most aggressive around parturition, and aggression levels decreased thereafter  <cit> .
pregnant laboratory rats, for example, more aggressively defend their nests against conspecific males and females  <cit> .
our results probably indicate a correlation between aggression and stress hormone levels and suggest that hormonal-mediated adaptive behavioural strategies help to minimise the risk of nest predation.
vole mothers in the presence of a heterospecific or conspecific competitor had higher fcm levels during the postpartum phase compared with the nest predator treatment and the prepartum phase.
increased resource competition  during lactation associated with higher aggression levels against competitors  <cit>  might have caused the elevated fcm levels.
CONCLUSIONS
vole mothers in our study showed behavioural and hormonal reactions specific to antagonist species.
the presence of a nest predator induced flexible behavioural adaptations during pregnancy to secure subsequent offspring survival, including modifications of the burrow architecture in combination with increased vigilance and nest guarding.
behavioural adaptations seem to be successful maternal strategies to balance typical postpartum parental investment trade-offs  and to secure fitness.
our results suggested differential adaptations as a result of co-evolution with a nest predator compared with resource competitors.
voles and shrews do not only compete in a ‘race for space’  but also in an ‘arms race’ in predatory and anti-predatory behaviour.

 communities are shaped by interspecific interactions and specific adaptations, depending on the nature of the interaction, allowing coexistence. effects of competition might be masked by behavioural adaptations as a result of a shared evolutionary history. studies of interspecific competition have mainly focused on how indirect exploitation competition affect behaviour, e.g., via territoriality and foraging strategy, and have neglected the implications of direct interference for community structure and evolution. direct antagonistic interactions in competition for food, space, nest sites, or mating partners can be very costly, especially if the competition reduces individual fitness. aggressive behavioural confrontations between competing species are likely if adults prey on each others offspring. interference may result from resource-related aggression between heterospecific or conspecific individuals with potential effects on niche use and community structure. nest predation has been considered a special case of direct interference via interspecific killing. it is a significant source of offspring mortality and can strongly affect parental life history strategies. although numerous population studies have shown that nest predation is widespread in animal communities, its importance as an evolutionary force has been neglected. recent studies on avian breeding biology demonstrate that the direct fitness effects of nest predation can drive evolution. safety of nest sites and optimised breeding conditions are key intrinsic components of breeding habitat quality. adults should adapt their behaviour to predation risk by, e.g., choosing concealed nest sites, adjusting clutch size or nestling period, and temporally partitioning foraging activity. comprehensive knowledge about adaptive strategies against nest predation in mammals is lacking. yet defence of a nest and its vulnerable young is a powerful explanation for the ultimate function of female aggression and territoriality, which is most intense during lactation and near the nest site. in addition, nests or burrows serve as micro-refuges from predators and therefore have anti-predatory benefits for the adult as well. parental anti-nest predatory behaviour according to parental investment theory, parents must trade off the benefits of investment into current offspring with possible negative effects on their future inclusive fitness. in addition, parents might suffer extra costs of defending offspring against predators, including time, energy, and missed opportunity costs. short-term adjustments are often trade-offs between behaviours, e.g., predator avoidance and foraging, and escalate in defending offspring against predators or infanticidal conspecifics. the degree of escalation is influenced by offspring vulnerability and reproductive value to the parent. female rodents become more aggressive during their pregnancy. female european rabbits increase vigilance during late pregnancy to minimise predation. in mice, mothers successfully defend their nestling pups against infanticidal conspecifics. attacks on pups decrease rapidly after they reach a less vulnerable stage. maternal defence behaviour against rattlesnakes declines in california ground squirrels as snake activity declines when pups grow older. according to the “harm to offspring hypothesis” of dale et al., the level of parental predation risk-taking is adjusted according to the harm the offspring will suffer without parental care. most vulnerable are altricial nestlings incapable of escaping and defending themselves. predation risk is highest when the parents are away. in response, parents might alter their foraging time or seek temporal or spatial foraging refuges to decrease risk. cresswell showed that nesting blackbirds altered their nest defence behaviour to compensate for predation risk demonstrating that parental behavioural flexibility in response to predation can yield fitness benefits compared with fixed strategies. for semi-fossorial mammals, the morphology and complexity of burrows have high defence value for nestlings and thereby fulfil an anti-predator function, especially for animals with helpless altricial young. hunting intruders might be confused by very complex burrow systems. some species dig special parturition chambers in addition to the main burrow and plug them to minimise predation. increased vigilance at burrow entrances and adjusting burrow attributes may further lower the risk of nest predation. physiological stress responses to nest predation risk physiological responses in stressful situations, e.g., encounters of prey with predators, are evolutionarily conserved and represent a widespread and fundamental mechanism for ecosystem functioning in animal systems. predator-induced changes in stress hormone metabolites associated with acute or chronic risks aim to increase survival. animals without adequate alternative defence responses to mitigate predation risk must engage in costly physiological responses. elevated plasma glucocorticoids, or their faecal metabolites, are often measured as indicators of such physiological stress responses. study system and hypotheses here we compare behavioural strategies among different interaction types: interspecific resource competition, intraspecific interference competition, and interspecific nest predation. we used a small mammal study system including the semi-fossorial common voles as focus animals, the greater white-toothed shrews as potential nest predators, and field voles as interspecific competitors. all three species coexist in many habitats of the northern hemisphere, overlapping in their common habitat and, to a smaller extent, in their diets. voles live in large burrow systems with underground tunnels and corresponding runway systems above ground. shrews explore vole tunnel systems to search for invertebrate food. because of the limited space underground, shrews may react aggressively when encountering tunnel inhabitants. additionally, they can act as nest predators on altricial vole nestlings by plundering their easily accessible nest chambers. this shrew behaviour might intensify during environmentally-adverse seasons when invertebrate food is scarce, e.g., in autumn. to protect vulnerable altricial nestlings from nest predators, voles should have evolved anti-nest predator strategies to secure their reproductive success. getz et al. reported nest defences in two american vole species, microtus pennsylvanicus and m. ochrogaster, even against larger shrew species, e.g., blarina brevicauda. shrews only successfully preyed on nests when vole mothers were absent on foraging trips. what kinds of parental behavioural strategies can secure nestling survival and allow the coexistence of competing species in a nest predator–prey system? how do these strategies differ from responses to non-nest predator antagonists? we hypothesised that vole mothers adjust their burrow systems in response to antagonists. if she encounters a nest predator during pregnancy, we expected to find different nest architectures at parturition than in the absence of predators. we further hypothesised that vole mothers react to nest predation risk by altering their time budgets and habitat use. to guard vulnerable nestlings, vole mothers should increase vigilance and nest guarding behaviour, especially during the first sensitive nestling phase. we expected guarding behaviour to be more intense in the presence of a potential nest predator than in the presence of an inter- or intraspecific resource competitor. in addition, if guarding behaviour incurs extra costs for vole mothers, e.g., owing to shortened foraging periods, we expected that to be reflected in the mother’s or nestlings’ body conditions. if vole mothers exhibit physiological stress reactions concomitant to these behavioural reactions, we expected levels of faecal corticosterone metabolites to correlate to the presence or absence of different antagonists. thus, we hypothesised that the levels of stress hormone metabolites in expectant vole mothers increased when they encountered shrews as nest predators.  behavioural adaptations: burrow architecture the numbers of burrow entrances built by vole mothers were significantly influenced by the type of antagonist. in the np treatment, they built fewer entrances compared with the rc or c treatments. the depth of the nest site was also influenced by antagonist type. mothers built nests closer to the surface in the np than in the rc or c treatments. behavioural adaptations: activity in burrow entrances the treatment species had a significant effect on the mothers’ activity in the burrow entrances. vole mothers in the np treatment spent more time in entrances compared with those in the rc or c treatments. the mean number of readings/bout and the mean number of seconds vole mothers spent in entrances per bout were not influenced by the antagonist species. we also recorded all treatment species entering the tunnel entrances. seventy-eight per cent of the shrews entered the burrow systems, while only 50% of the field voles and 43% of common voles did so, but the latter two species visited the burrow system more often per replicate than did the shrews. the number of antagonist visits to the vole burrow was recorded using automatic transponder-reading antennas inserted into tunnel entrances. stress hormone level we found no difference in the baseline amount of fcms before the treatments. under treatment conditions, fcms were affected by an interaction of treatment and sampling. mothers in np treatments had a higher fcm levels around parturition compared with the other treatments and compared with the postpartum period. the fcm of vole mothers did not differ any more between treatments when nestlings were d old. non-significant post hoc results are not displayed. maternal body condition and offspring survival we found no influence of treatment on the vole mother’s body weight, either prepartum nor postpartum. we also found no influence of antagonist species on offspring survival. both the number of vole nestlings and nestling body weight were independent of antagonist species. discussion we investigated behavioural and physiological responses of vole mothers to different intra-nest interactions: nest predation, interspecific resource competition, and intraspecific competition. nest predators affected burrowing behaviour and passage activity at burrow entrances as well as physiological stress responses. the presence of neither a potential nest predator nor a competitor species altered reproductive success. furthermore, nestlings in all treatments were in good condition. these results indicate that vole mothers seem to perceive shrews as a threat and adequately respond to their presence. treatment animals of all antagonist species visited the vole mothers’ burrow system several times. vole mothers were apparently successful in defending their nestlings against potential nest predation attempts. adaptive anti-nest predatory strategies pregnant common voles responded to the presence of a potential nest predator or a resource competitor with different nest site preparations. contrary to findings on african gerbil and prairie vole mothers, which build complex burrow systems to confuse predators or to hide nestlings, the common voles in our study constructed simpler burrow systems in the presence of nest predators, but not when a competitor species was present. nest defence might be more efficient in a basic burrow system than in a complex one. additionally, simpler refuges might help to reduce interactions with antagonists and avoid unnecessary energetic costs, as in complex tunnel systems. another explanation might be that pregnant females without nest predation pressure stayed in their prepartum burrow, while pregnant females threatened with a nest predator may have dug a new, isolated nest site, as shown in laboratory rats and european rabbits. by preparing the nest site prepartum, mothers might try to avoid spending energy postpartum in digging and guarding the nestlings. these findings agree with the “harm to offspring” hypothesis, which predicts that mothers should minimise periods of vulnerability during parental absence. common vole burrow traits in the presence of a heterospecific competitor might reflect a general necessity for nestling protection against possible intruders. harper and batzli found no strong effect on the burrowing behaviour of prairie voles by the presence of heterospecific meadow voles. although heterospecific resource-related aggression can have similar consequences to predation effects, vole mothers seemed to differentiate between the risks of heterospecific aggression and nest predation. nest guarding and vigilance behaviour as indicators of the perceived predation risk suggest that vole mothers have adapted to shrews as nest predators through a shared evolutionary past. only in the presence of shrews did vole mothers spent long time periods in the burrow entrances. increase of vigilance is a common response to predator odour. for example, female european rabbits increased their vigilance, especially during late pregnancy, to deter attacks by potential predators. female mammals must allocate their time among maternal care, foraging, and vigilance, especially during the first days of nestling life. in some species, this trade-off adversely affects the condition of pregnant or lactating females. we found no effect of increased vigilance in the shrew treatment on neither maternal nor nestling body weight. other studies with simulated predation risks also demonstrated stable food intake, despite increased vigilance. vigilance and foraging during the energetically-demanding reproductive phase are therefore not mutually exclusive, and mothers in our experiment were able to successfully protect their young against nest predators without suffering energetic costs. this finding might not apply under natural conditions, e.g., if food for shrews is scarce and shrews exert higher predation pressure on vole nestlings. physiological stress responses to nest predation the physiological stress response to the presence of a nest predator during late pregnancy was higher than in other competitor treatments or in the postpartum phase. a few days after parturition, the levels of fcms decreased almost to pre-treatment baseline levels. female rodents were most aggressive around parturition, and aggression levels decreased thereafter. pregnant laboratory rats, for example, more aggressively defend their nests against conspecific males and females. our results probably indicate a correlation between aggression and stress hormone levels and suggest that hormonal-mediated adaptive behavioural strategies help to minimise the risk of nest predation. vole mothers in the presence of a heterospecific or conspecific competitor had higher fcm levels during the postpartum phase compared with the nest predator treatment and the prepartum phase. increased resource competition during lactation associated with higher aggression levels against competitors might have caused the elevated fcm levels.  vole mothers in our study showed behavioural and hormonal reactions specific to antagonist species. the presence of a nest predator induced flexible behavioural adaptations during pregnancy to secure subsequent offspring survival, including modifications of the burrow architecture in combination with increased vigilance and nest guarding. behavioural adaptations seem to be successful maternal strategies to balance typical postpartum parental investment trade-offs and to secure fitness. our results suggested differential adaptations as a result of co-evolution with a nest predator compared with resource competitors. voles and shrews do not only compete in a ‘race for space’ but also in an ‘arms race’ in predatory and anti-predatory behaviour. 
further, we measured pre- and postpartum faecal corticosterone metabolites of mothers to test for elevated stress hormone levels. voles displayed an adequate behavioural response for both resource competitors and nest predators. our study revealed differential behavioural adaptations to resource competitors and nest predators. we studied behavioural adaptations of vole mothers during pregnancy, parturition, and early lactation, specifically modifications of the burrow architecture and activity at burrow entrances. behavioural adaptationssmall mammalsinterspecific interactionsnest predationstress responsefaecal corticosterone metabolitesburrow systemshrewsvoles although the presence of both the shrew and the field vole induced prepartum modifications to the burrow architecture, only nest predators caused an increase in vigilance time at burrow entrances during the sensitive nestling phase. adaptive behavioural strategies promoting co-occurrence of competing species are known to result from a sympatric evolutionary past. they modified burrow architecture to improve nest guarding and increased their vigilance at burrow entrances to enhance offspring survival chances. focus common vole mothers were either caged with a greater white-toothed shrew as a potential nest predator, with an herbivorous field vole as a heterospecific resource competitor, or with a conspecific resource competitor. strategies should be different for indirect resource competition than for direct interspecific interference. we studied the effects of resource competition and nest predation in sympatric small mammal species using semi-fossorial voles and shrews, which prey on vole offspring during their sensitive nestling phase. only in the presence of the nest predator were prepartum fcms elevated, but we found no loss of vole nestlings and no differences in nestling body weight in the presence of the nest predator or the heterospecific resource competitor.
 adaptive behavioural strategies promoting co-occurrence of competing species are known to result from a sympatric evolutionary past. strategies should be different for indirect resource competition than for direct interspecific interference. we studied the effects of resource competition and nest predation in sympatric small mammal species using semi-fossorial voles and shrews, which prey on vole offspring during their sensitive nestling phase. experiments were conducted in caged outdoor enclosures. focus common vole mothers were either caged with a greater white-toothed shrew as a potential nest predator, with an herbivorous field vole as a heterospecific resource competitor, or with a conspecific resource competitor.  we studied behavioural adaptations of vole mothers during pregnancy, parturition, and early lactation, specifically modifications of the burrow architecture and activity at burrow entrances. further, we measured pre- and postpartum faecal corticosterone metabolites of mothers to test for elevated stress hormone levels. only in the presence of the nest predator were prepartum fcms elevated, but we found no loss of vole nestlings and no differences in nestling body weight in the presence of the nest predator or the heterospecific resource competitor. although the presence of both the shrew and the field vole induced prepartum modifications to the burrow architecture, only nest predators caused an increase in vigilance time at burrow entrances during the sensitive nestling phase.  voles displayed an adequate behavioural response for both resource competitors and nest predators. they modified burrow architecture to improve nest guarding and increased their vigilance at burrow entrances to enhance offspring survival chances. our study revealed differential behavioural adaptations to resource competitors and nest predators. behavioural adaptationssmall mammalsinterspecific interactionsnest predationstress responsefaecal corticosterone metabolitesburrow systemshrewsvoles 