Measure Of Territory Quality Research Articles

Trophic Niche in a Raptor Species: The Relationship between Diet Diversity, Habitat Diversity and Territory Quality.

Recent research reports that many populations of species showing a wide trophic niche (generalists) are made up of both generalist individuals and individuals with a narrow trophic niche (specialists), suggesting trophic specializations at an individual level. If true, foraging strategies should be associated with individual quality and fitness. Optimal foraging theory predicts that individuals will select the most favourable habitats for feeding. In addition, the “landscape heterogeneity hypothesis” predicts a higher number of species in more diverse landscapes. Thus, it can be predicted that individuals with a wider realized trophic niche should have foraging territories with greater habitat diversity, suggesting that foraging strategies, territory quality and habitat diversity are inter-correlated. This was tested for a population of common kestrels Falco tinnunculus. Diet diversity, territory occupancy (as a measure of territory quality) and habitat diversity of territories were measured over an 8-year period. Our results show that: 1) territory quality was quadratically correlated with habitat diversity, with the best territories being the least and most diverse; 2) diet diversity was not correlated with territory quality; and 3) diet diversity was negatively correlated with landscape heterogeneity. Our study suggests that niche generalist foraging strategies are based on an active search for different prey species within or between habitats rather than on the selection of territories with high habitat diversity.

Life-history tradeoffs in Spotted Owls (Strix occidentalis): Implications for assessment of territory quality

ABSTRACT. Tradeoffs among life-history traits have long provided material for evolutionary studies of life-history strategies but can also have practical implications for assessments of habitat and territory quality in species of conservation concern. Here, we characterize tradeoffs between parental reproductive output and offspring fitness in a closed population of California Spotted Owls (Strix occidentalis occidentalis) using multistratum mark-recapture models and evaluate how potential tradeoffs influenced measures of territory quality. We detected heterogeneity in offspring survival associated with parental reproductive output; individuals that fledged in pairs had a greater probability of surviving than individuals that fledged either as singletons or in triplets, an advantage that was evident in juvenile, subadult, and adult life stages. Thus, the survivorship of offspring that fledged in pairs was high despite costs associated with producing a second fledgling, but the demands of producing a third...

The effects of perch height, time in residence and distance from opponent on aggressive display in male lizards

In antagonistic encounters individuals' displays reflect both the quality of the resource under dispute and their perception of the threat posed by their rival. All else being equal, as the value or threat to contested resources increases, so should an individual's level of aggression. Using a territorial species of Australian agamid lizard, the tawny dragon (Ctenophorus decresii), we tested three hypotheses about the relationship between territory quality and aggression. In three experiments we measured aggression whilst manipulating time in residence, perch height as a measure of territory quality and distance to an opponent's territory. Our measurement of aggression was a summary of behaviours used by tawny dragons in antagonistic displays (wrestling, hind-leg push-up display, chasing, raising of nuchal or vertebral crests, back arching, lateral compression, lowering dewlap, jerky walk and tail flick). Animals had significantly lower aggression scores when the opponent's territory was further away, but time in residence and perch height did not affect our measures of aggression. These experimental results provide good grounding for further tests of these hypotheses in field scenarios specifically manipulating distance between neighbours to determine what maintains the spatial distribution of tawny dragons in the wild.

Population regulation by habitat heterogeneity or individual adjustment?

1. The habitat heterogeneity (HHH) and individual adjustment (IAH) hypotheses are commonly proposed to explain a decrease in reproduction rate with increasing population density. Higher numbers of low-quality territories with low reproductive success as density increases lead to a decrease in reproduction under the HHH, while more competition at high density decreases reproduction across all territories under the IAH. 2. We analyse the influence of density and habitat heterogeneity on reproductive success in eight populations of long-lived territorial birds of prey belonging to four species. Sufficient reliability in distinguishing between population-wide, site-specific and individual quality effects on reproduction was granted through the minimal duration of 20 years of all data sets and the ability to control for individual quality in five of them. 3. Density increased in five populations but reproduction did not decrease in these. Territory occupancy as a surrogate of territory quality correlated positively with reproductive success but only significantly so in large data sets with more than 100 territories. 4. Reproductive success was always best explained by measures of territory quality in multivariate models. Direct or delayed (t-1) population density entered very few of the best models. Mixed models controlling for individual quality showed an increasing reproductive performance in older individuals and in those laying earlier, but measures of territory quality were also always retained in the best models. 5. We find strong support for the habitat heterogeneity hypothesis but weak support for the individual adjustment hypothesis. Both individual and site characteristics are crucial for reproductive performance in long-lived birds. Proportional occupancy of territories enables recognition of high-quality territories as preferential conservation targets.

Predicting the breeding success of large raptors in arid southern Africa: a first assessment

Raptors are often priorities for conservation efforts and breeding success is a target measure for assessing their conservation status. The breeding success of large raptors in arid southern Africa is thought to be higher in years of high rainfall. While this correlation has been found in several studies, it has not yet been shown for data from a wider geographical area. In conservation research, it is important to explore the differences between spatially-separated populations to estimate and to compare their conservation status, and to deduce specific management strategies. Using a theoretical approach, we develop a simplistic model to explain the breeding success-rainfall relationship in large African raptors at larger spatial scales. Secondly, we validate this model and we show that the inclusion of field data leads to consistent predictions. In particular, we recommend that the average size of the 'effective territory' should be included in the relationship between annual rainfall and breeding success of raptors in arid southern Africa. Accordingly, we suggest that breeding success is a function of precipitation and inter-nest distance. We present a new measure of territory quality depending on rainfall and territory size. We suggest that our model provides a useful first approach to assess breeding success in large raptors of arid southern Africa. However, we strongly emphasise the need to gather more data to further verify our model. A general problem in conservation research is to compare the status of populations assessed in different study areas under changing environmental conditions. Our simplistic approach indicates that this problem can be overcome by using a weighted evaluation of a target measure (i.e. breeding success), taking regional differences into account.

Occupancy as a measure of territory quality

SummaryTerritory quality may affect individual fitness and contribute to density‐dependent reproduction, with repercussions on population regulation. We investigated the probable causes and population consequences of spatio‐temporal variations in territory quality, measured by occupancy, in eight black kiteMilvus migransBoddaert populations, one of them studied for 10 years (Lake Lugano) and the rest for 4–5 years.Over a period of years, the occupation rate of territories varied from a random pattern. Some territories were preferred while others were avoided. On return from migration, males and females settled earlier on high‐occupancy territories.The positive association between territory occupancy and breeding performance held in all years of study at Lake Lugano, and in six of seven tested populations. As a result, high‐occupancy territories contributed most of the young produced by each population.The occupation rate of the overall 225 territories was related positively to food availability and negatively to mortality risk, measured as proximity to the nearest eagle owlBubo buboLinnaeus nest.At the population level, spatial variation in mean occupancy was positively correlated with spatial variation in mean productivity, suggesting that mean occupancy could be used as a measure of overall habitat quality and population performance.In the Lake Lugano area, a higher proportion of low quality territories was occupied in years of higher density and annual productivity was related negatively to its coefficient of variation. However, annual productivity was not related significantly to the proportion of low quality territories occupied, so support for the theory of site‐dependent population regulation was only partial.In a review of 22 studies of territory occupancy in 17 species, occupancy always deviated from a random pattern in species in which it was tested and was always correlated with productivity and/or with some other measure of territory quality. Our results confirm the importance of prioritizing conservation of high quality territories. Occupancy may be a reliable method of quality assessment, especially for populations in which not all territories are always occupied, or for species in which checking occupancy is easier than finding nests.

Nest-site selection of the Long-eared Owl Asio otus in northwestern Switzerland

Capsules Sites are selected as part of an antipredator strategy. Aims To assess if site choice depends on habitat variables at nest sites and if habitat quality influences reproduction. Methods Breeding density was explored in northwestern Switzerland from 1992 to 1996. Habitat variables were examined at 38 breeding sites and were compared with data collected from random sites. Habitat quality was estimated using the discriminant function scores of the nesting sites. Results Breeding density was found to vary between years; more pairs bred and raised more young in 1993, a year of high vole abundance. Long-eared Owls tended to avoid the vicinity of buildings; they occupied sites with denser forest edges, greater canopy cover, and with more conifers than random sites. I found no statistical evidence that they used less optimal sites when the population was high. The number of fledglings increased with habitat quality, but did not vary with any of the habitat variables taken separately. Conclusion Long-eared Owl selects nesting habitat as part of an anti-predator strategy, but the measures of territory quality did not seem to be a limiting factor for the population.

Male size does not affect territorial behaviour and life history traits in a sphecid wasp

The optimum maternal investment per offspring is determined by the relationship between the investment per offspring and offspring fitness. In the European beewolf, Philanthus triangulum, a solitary mass-provisioning sphecid wasp, offspring size correlates with the amount of provisions. We investigated whether the reproductive success of adult males depends on body size in a way that would influence the allocation of parental investment. Since the mating success ofP.triangulum males cannot be determined by observation in the field, we assessed the influence of male size on characteristics of their territories, territorial behaviour and life history traits. Territory size was weakly correlated with male size, but a measure of territory quality (number of female nests in the vicinity) was independent of male size. Neither the duration of ownership nor the intensity of scent marking was correlated with male size. Territory owners were slightly smaller than nonterritorial males. The absolute amount of fat was positively correlated with size but, owing to allometric relationships, the energetic equivalent of the fat store appeared to be independent of size. Life span was not significantly influenced by body size under four different conditions (with and without food in the laboratory, in an outdoor flight cage and in the field). We discuss the discrepancy between these results and other studies that have mostly reported advantages to large males. We suggest that in noncontact male–male interactions, as seen in the European beewolf, body size might not be the key determinant for success in contests. We conclude that there is no evidence for a strong size dependence of male reproductive success. Thus the reproductive success of male progeny probably does not depend on parental investment in a way that would influence the investment allocation of females.

Correlates of Hoot Rate and Structure in Male Tawny Owls Strix aluco: Implications for Male Rivalry and Female Mate Choice

The patterned hooting of owls may serve one or more functions including repulsion of territorial invaders, attraction of potential mates, and stimulation of the mate. In this study I looked for characteristics in the Tawny Owl hoot which might convey information on the signaller's quality or that of its territory to potential mates and rivals. I therefore analysed relationships between hooting rate, hoot harshness and 13 structural features of the hoots of 22 territory-defending male Tawny Owls on the one hand, and male RHP (i.e., aggressiveness in response to playback), territory size, stability, patchiness, fragmentation and owl reproductive output on each territory on the other. Hooting rate, hoot harshness and rhythm were all related to male RHP, but not to any measure of territory quality. These features therefore appeared to reflect aspects of male competitive potential, i.e. the male's quality as a defender. By contrast, duration and frequency range of notes were related to reproductive output and territory stability, possibly signalling better territories in terms of resources and better male parental performance. Males involved in territorial contests increased their hooting rate when females joined them in a communal response. This more conspicuous display, rather than functioning as a mate guarding strategy, may be interpreted as a means of influencing female choice directly.

Mate choice by marsh wrens: the influence of male and territory quality

If females choose breeding situations to maximize their fitness, then those features of the male and/or territory that are important in mate selection by females should affect female fitness, be assessable prior to mating, and vary among males. The purpose of this study was to identify characteristics of male quality and territory quality that fit these criteria for marsh wrens Cistothorus palustris. The male's contribution to nest defence appeared not to affect female success or choice. However, females that received male assistance with feeding young produced more and heavier fledglings than females without assistance. Males that fed young did not attract more mates. Few males in this population fed young, and no relationship was found between feeding effort and physical or behavioural features of the male. Results of multivariate analyses suggest that, within sites, the measures of territory quality used here cannot explain the variance in the number of young fledged per female or male harem size. The examination of arbitrary territories showed that male pairing success, female settlement order and predation patterns were not significantly correlated between years. The results suggest that territory quality does not influence female success or choice. These results are discussed in the light of earlier attempts to relate features of males and territories to mate selection by female passerines.

The effects of helpers in cooperatively breeding purple gallinules

The effects of helpers in a population of cooperatively breeding purple gallinules (Porphyrula martinica) were examined. All young birds past the age of 2 months helped feed and protect subsequent broods of chicks and participated in territorial defense. Most helpers remained on their natal territories for approximately 1 year. The number of helpers varied both among and within breeding groups. Clutch production and chick survival were related positively to the number of helpers in the group. The increase in chick survival was independent of several measures of territory quality. Helpers possibly aided chick survival by provicing extra food for the chicks and decreasing predation risk. Helpers were necessary in order for a breeding pair to keep a territory long enough to produce more than one clutch of eggs. A change in the number of helpers (increase or decrease) often was followed by a similar change in territory size. These results suggest that purple gallnule helpers can increase the reproductive success of the breeding group and may be vital for the continued maintenance of a breeding territory.