Factors affecting the distribution of Red-legged Partridges Alectoris rufa in an agricultural landscape of southern Portugal

The main factors affecting the spring distribution of Red-legged Partridges Alectoris rufa were evaluated in a 1550-km² landscape of southern Portugal, where different arable systems and hunting regimes were implemented. Partridge surveys were performed in April 1995 along 90, 250-m transects. Partridge locations and a number of environmental variables were incorporated and manipulated in a vector-based GIS. A multivariate logistic model of partridge detection was fitted using forward stepwise selection, and was validated using a jack-knife approach. The probability of detecting Red-legged Partridges within the landscape was positively affected by game management, structural diversity of cover, proportion of olive tree groves and wheat fields along the transects. Conservation implications of the results and research priorities are discussed.     

The survival of gamebird (Galliformes) chicks in relation to pesticide use on cereals

Field experiments were carried out to test the effects of cereal pesticides (herbicides, fungicides and insecticides) on chick survival of Grey Partridge Perdix perdix , Red-legged Partridge Alectoris rufa and Pheasant Phasianus colchicus. On fields in experimental plots the outer 6 m of cereal (the headland) were not sprayed with pesticides from 1 January 1984, whereas control plots were fully sprayed. Gamebird brood counts were carried out after the cereal harvest. In addition, nine Grey Partridge broods were radio-tracked for 21 days after hatching (four in sprayed plots and five in unsprayed plots) to determine their movements, home range size and survival in relation to pesticide spraying.
The mean brood size of Grey Partridge and Pheasant was significantly higher on plots where field edges were unsprayed than on fully sprayed control plots. Data for Red-legged Partridge were inconclusive. The survival of individually marked Grey Partridge broods was negatively related to the distance moved between successive nocturnal roost sites. Survival was significantly higher, the distance moved between roost sites significantly shorter and the proportion of home range including headland significantly greater for broods feeding in spring barley fields with unsprayed field edges compared with broods feeding in fully sprayed fields.     

Species differences in diet and the development of seed digestion in partridge chicks Perdix perdix and Alectoris rufa

Chicks of both the Grey and the Red-legged Partridge feed on arthropods and plant material, mainly leaves and seeds. Fully grown partridges are mainly herbivorous and the proportion of plant material eaten increases rapidly during early life in both species, but plant material predominates in the diet of the Red-legged Partridge from an earlier age than for the Grey Partridge. Red-legged Partridge chicks are also able to disrupt grass seeds efficiently during passage through the digestive tract from an earlier age (2 days) than Grey Partridge chicks (10 days). It is suggested that the difference in timing between species in the development of herbivory is associated with this difference in digestive ability.     

Land use and environmental factors affecting red-legged partridge (Alectoris rufa) hunting yields in southern Spain

The red-legged partridge is a small game species widely hunted in southern Spain. Its commercial use has important socioeconomic effects in rural areas where other agrarian uses are of marginal importance. The aims of the present work were to identify areas in Andalusia (southern Spain) where game yields for the red-legged partridge reach high values and to establish the environmental and land use factors that determine them. We analysed 32,134 annual hunting reports (HRs) produced by 6,049 game estates during the hunting seasons 1993/1994 to 2001/2002 to estimate the average hunting yields of red-legged partridge in each Andalusian municipality (n=771). We modelled the favourability for obtaining good hunting yields using stepwise logistic regression on a set of climatic, topographical, land use and vegetation variables that were available as digital coverages or tabular data applied to municipalities. Good hunting yields occur mainly in plain areas located in the Guadalquivir valley, at the bottom of Betic Range and in the Betic depressions. Favourable areas are related to highly mechanised, low-elevation areas mainly dedicated to intensive dry crops. The most favourable areas predicted by our model are mainly located in the Guadalquivir valley.     

An ethological perspective on defecation as an integral part of anti-predatory behaviour in the grey partridge (<Emphasis Type="Italic">Perdix perdix</Emphasis> L.) at night

Night-time flight behaviour of the grey partridge (Perdix perdix) was studied in three agricultural landscapes in Germany during the winter of 2005/2006. Thermography was used to detect roosting coveys and record flight behaviour. The main focus of the study was an analysis of defecation behaviour during the escape flight. A total of 640 partridges in 102 coveys were detected and approached during 85 scanning hours. Flight initiation distance averaged 22.8 m. In at least 75% of the coveys, defecation occurred upon being flushed. A covey of 15 partridges can produce 60 droppings that appear as a shower on the thermal record distributed over an estimated area of 200 m2. It can be hypothesised that defecation in the context of escape behaviour has various selective advantages in addition to the reduction of body weight. Predators may be irritated or deterred by the excretion of faeces of the partridges taking off. As defecation also appears in flushed partridges not in an immediate life-threatening situation, this behaviour seems to be uncoupled from the parasympathetic reaction of fear. Permanent predator pressure may have selected for a strategic integration of defecation in the escape behaviour of partridges at night.     

The reproductive biology of the Rock Partridge Alectoris graeca saxatilis in the southern French Alps: first evidence of double-nesting behaviour

Capsule: Double-nesting occurs frequently in Rock Partridges Alectoris graeca living in the southern French Alps.

Aims: To investigate reproductive parameters of a Rock Partridge Alectoris graeca population.

Methods: The reproductive behaviour of 62 radio-tagged birds was monitored during the breeding seasons 2012–16, to record breeding phenology, clutch sizes, hatching success, nest survival and parental care.

Results: Double-nesting behaviour in the Rock Partridge was confirmed for the first time. Participation in incubation was similar for males and females (86% versus 70%). Clutch size was larger for nests incubated by males (11.0?±?1.6 eggs) than by females (9.5?±?1.2). Male nest survival rate (0.37) tended to be lower than female nest survival rate (0.62), although the difference was not significant. No significant difference was detected between male and female hatching success. Nest failures were caused by mammals taking the eggs (78%) or predation of the incubating parent (13%). Some circumstantial evidence suggests that occurrence of double-nesting behaviour could depend on previous winter and spring weather influencing the body condition of females. The reproductive biology of the Rock Partridge contrasts in some breeding traits with Red-legged Partridge and natural partridge hybrids, possibly due to climatic differences between habitats.

Conclusion: Confirmation of double-nesting in Rock Partridges indicates that climatic constraints inherent to its mountain environment do not act as an impediment to this behaviour. Variation in weather conditions between years could influence the annual occurrence of double-nesting.     

On the efficiency of using song playback during call count surveys of Red-legged partridges (<Emphasis Type="BoldItalic">Alectoris rufa</Emphasis>)

Successful management practices for declining bird species depend often on long-term surveys acquired by point counts. Despite high standardization of field protocols, uncertain detection probability remains an important source of variability and bias in point-count data. This effect is of main importance in low-responsive species as the Red-legged partridge (Alectoris rufa), but it can be counterbalanced, increasing detection probability. In this 2-year study, we sampled using traditional point-count methods, followed by playback sessions for each repetition. We measured detection probability and the efficiency of playback for detectability in the context of a feasibility study on long-term point-count surveys for a harvested game bird, the Red-legged partridge. The results for both study years show a distinct increase in detection probability (23% and 45%, respectively) when using playback vs. the traditional point-count method. We also tested our results for heterogeneity, trap dependence, and time dependence, and no effect was detected. Thus, we suggest that the future design of long-term surveys on Red-legged partridges should consider abundance indices using playback sessions.     

A Comparison of Methods for Estimating Northern Bobwhite Covey Detection Probabilities

Abstract: We compared the time-of-detection and logistic regression methods of estimating probability of detection for northern bobwhite (Colinus virginianus) coveys. Both methods are unusual in that they allow estimation of the total probability of detection (i.e., the product of the probability that a covey is available for detection [i.e., that a covey vocalizes] and detection given availability). The logistic regression method produced an average detection probability of 0.596 (SE = 0.020) and the time-of-detection method produced a detection probability estimate of 0.540 (SE = 0.086), and the 2 estimates were not significantly different. This is the first evaluation of the time-of-detection method with empirical field data. Although the time-of-detection and logistic regression method each have advantages, both can be used under appropriate conditions to improve estimates of bobwhite abundance by allowing for the estimation of detection probabilities. Improved estimates of bobwhite abundance will allow land managers to make more informed management decisions.     

Machine learning and GIS-RS-based algorithms for mapping the groundwater potentiality in the Bundelkhand region,India

Mapping the groundwater potential zones with high accuracy is always a difficult task. The combination of Geographic Information System (GIS) and Remote Sensing (RS) with machine learning techniques provide a reliable method to map the groundwater prospective areas. This research used support vector machine (SVM) learning and random forest (RF) regression algorithms to predict the groundwater potential areas in the Bundelkhand craton region. All the parameters that affect the groundwater occurrence in this region, such as altitude, aspect, distance to drainage, distance to road, distance to faults, geomorphology, distance to river, lithology, normalized difference vegetation index (NDVI), rainfall, slope, soil, drainage density, land use land cover (LULC), topographic wetness index (TWI), lineament density and curvatures have been prepared by the remote sensing data as well as data taken from different departments and organizations. The training and testing dataset is generated from the groundwater potential zones map prepared through the frequency ratio (FR) technique. A total of 23,917-pixel locations have been selected in the research region. These locations contain the location of groundwater points and non-groundwater points equally. These points were randomly portioned into 70:30 for training and testing the model, respectively. The 2417 unknown points were taken from the study area and given to the trained model to predict the groundwater prospective areas. The maps of groundwater potential zones obtained using machine learning models were categorized into five classes: very low, low, moderate, high, and very high. The outcome of the employed algorithm is validated through the well discharge data and area under the receiver operating characteristics curve (AUC-ROC) method. The developed model's outcome gives valuable information regarding the effective management of groundwater in a particular region to government agencies and private sectors.     

Habitat selection by two predators in an urban area: The stone marten and red fox in Wrocław (SW Poland)

We analyzed the habitat use of stone martens and red foxes based on incidental observations within the urbanized zone of Wrocław, SW Poland. We compared proportional habitat use at observation sites with randomly selected points and evaluated differences in distance to the water sources and to urban boundaries. Habitat use by both species was different from what we had expected from random points. Stone martens used high-density housing more frequently than red foxes and that expected from random points and avoided open and industrial areas, whereas red foxes used housing estates significantly more often than expected and avoided high-density housing. Both species used the other habitats according to their availability. Stone martens often selected habitats located closer to the city centre, whereas red foxes often selected habitats closer to urban borders than expected. The distribution of red foxes and stone martens is influenced by several factors including the availability of shelter and food, as well as the opportunity to move around undetected. Interspecific competition may also play an important role in habitat selection. Stone martens seem to be better adapted to urbanized areas than red foxes.     

Survival and causes of mortality among wild Red-legged Partridges Alectoris rufa in southern Spain: implications for conservation

Knowledge of intrinsic and extrinsic factors associated with survival rates and the underlying causes of mortality is essential to understand both population dynamics and the causes of population declines. We studied the influence of habitat variables and body condition on survival of 151 radio‐tracked Red‐legged Partridges Alectoris rufa in four areas of Spain, representing a gradient from natural unmanaged areas to highly managed areas. We examined the effects of differences in game management practices, and seasonal and geographical variations in survival and causes of mortality over 4 years, from 1999 to 2002. Monthly survival rate was consistently over 90% for both sexes in the natural area. However, in two areas managed intensively for both hunting and agriculture, survival was low during the hunting period (72% for females and 79% for males), high during the breeding period for males (99%), and intermediate for females (89%) due mainly to diseases. Hunting was the main cause of Red‐legged Partridge mortality in both hunting areas where driven partridge shooting was performed, affecting 50% of radio‐tagged individuals, and was the main cause of mortality over all areas during both breeding and hunting periods. Disease was the next most common cause of mortality in managed areas, affecting mostly females during the breeding period, whereas predation was the main cause of mortality in unmanaged populations. Finally, we compared the habitat associations and body condition of living and dead individuals with varying causes of mortality. In general, high survival rates were associated with diverse vegetation, habitat edges and a good body condition index. Habitat diversity and a high edge index were also negatively associated with mortality due to predation and diseases. On the other hand, hunting mortality decreased with the proportion of scrubland and increased with the proportion of agricultural land. These results suggest that preventing declines of wild Red‐legged Partridge populations might best be achieved by increasing landscape complexity and connectivity, and promoting game management practices to limit both partridge bags and long‐term densities.     

Factors affecting changes in grey partridge population dynamics in a French arable farmland over an eleven-year period

The grey partridge Perdix perdix is of conservation concern owing to habitat heterogeneity losses and the negative impact of other environmental factors, e.g., pesticide use, predators, weather or shooting pressure, which are known to be associated with population decline. By an 11-year-period study in an intensively cultivated farmland located in the Paris basin, we aimed to relate the changes in grey partridge population dynamics with the changes in agriculture, monthly rainfall and shooting pressure. Summer drought occurred at the middle time of the study period. At the start of our study, a new cultivation, winter-wheat broadcast in maize-stubble fields, was introduced that probably improved the habitat. But in the next years, there was a loss in habitat diversity due to the disappearance of pastures dedicated to sheep rearing, removal of non-cropped areas and field boundaries and increase in the mean field size. Shooting was annually adjusted to what the owner believed to be a wise harvest. In post-breeding coveys, both percentages of hens with young among total hens and young-to-successful hens ratios first increased and then decreased. The mean brood size was rather weak during the dryness incident. The number of pairs in a more heterogeneous sector was always greater than in a less one. In both sectors, spring abundance first increased and then decreased. In the second half of the study period, the shooting quotas were reduced, especially when the mean brood size fell down. Low hatching rates of clutches and low chick survival rates explain the population decline, as the results are convincing. To stop the population decline in intensive arable farmland, good breeding success is needed. This can be provided by favourable habitats for hens to nest and for chicks to feed.     

Foraging behaviour and habitat partitioning of two sympatric cormorants in Patagonia, Argentina

Radiotelemetry was used to assess the distribution and diving behaviour of Rock Shags Phalacrocorax magellanicus and Red-legged Cormorants Phalacrocorax gaimardi breeding in sympatry, and Rock Shags breeding in isolation. When breeding in sympatry there was little overlap in the foraging locations of the two species, with the highest densities of each species separated by 10 km. Red-legged Cormorants fed significantly closer to the breeding colony than did Rock Shags and undertook shorter foraging trips, making almost twice as many foraging trips per day as Rock Shags. Rock Shags breeding in isolation had a shorter foraging range than the birds breeding in sympatry with Red-legged Cormorants and foraging trip duration was significantly shorter. However, the number of feeding trips per day was similar between areas of sympatry and allopatry. Differences in the foraging ecology of Rock Shags in areas of sympatry and allopatry may be due to interspecific competition, which forces niche differentiation. The distance between foraging sites, the speed of movement of the prey, a species tendency to move into prey-depleted areas and the length of the breeding season (during which the birds are constrained to be in the same area) may play critical roles in determining the extent to which differential area use by competitors is a strategy that benefits both parties.     

Availabilty of juveniles from natural sources of the oyster Pteria colymbus (Bivalvia: Mytilidae), in the Gulf of Cariaco, Venezuela

We examined the spat availability the oyster Pteria colymbus at 6-8 and 19-21 m depths for 15 months (March 1993-June 1994) in Turpialito, Golfo de Cariaco, Venezuela. Spats were trapped using artificial collectors (plastic filaments in bags, 30 x 60 mm), suspended from a long line. Each collector was replaced by a replica monthly to analyse abundance, shell dimension and mass of P. colymbus. Intraweekly, the temperature, salinity, oxygen and food availability (Chlorophyll a, total seston, organic and inorganic seston) were determinated. There is juvenile recruitment all year, suggesting continuous reproduction. Spat counts were higher at 6-8 m (generally 50-230 juveniles per collector) with peaks in August and December 1993 (April and June 93 at 19-21 m). The length-weigh mass relation was higher at 19-21 m, suggesting greater food availability because of lower organism density (including P. colymbus) and a greater water flux. Phytoplanktonic abundance and temperature were correlated (r2=0.38) with juvenile abundanc; this relationship and the association of juvenile abundance with higher temperature and Chlorophyll a levels, suggest that spat abundance was higher at the beginning of the water stratification period, when phytoplankton biomass is high.     

Effect of Game Management on Wild Red-Legged Partridge Abundance

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 post-breeding 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.     

Bird species numbers in an archipelago of reeds at Lake Velence, Hungary

1 Bird species numbers were studied on 109 reed islands at Lake Velence, Hungary, in the 1993 and 1994 breeding seasons. The aim was to describe and account for the abundance and distribution patterns of the bird species. 2 It was expected that an exponential model would fit the calculated species–area curves. However, for the 1993 data, both the power function (LogS ~ LogArea) and the exponential (S ~ LogArea) models did so, while the power function, exponential and linear (S ~ A) models fitted the curves for the 1994 data. 3 The results showed that the pattern was not random: a collection of small islands held more species than a few large islands with the same total area. 4 The relative species richness of small islands is a result of the preference of most common passerine bird species for the edges of reed islands. Most individuals were found in the first 5 m of the reedbed, and no edge avoidance was detected on a local spatial scale. Large, rarer species (e.g. Great White Egret), however, were found to be dependent on large reed islands. 5 Comparison of results with two other studies on bird communities of reed islands revealed that the type of landscape matrix (e.g. deep water, shallow water or agricultural lands) among reed patches significantly influences bird communities. Deep water was dominated by grebes and coot, shallow water by reed‐nesting passerines, and farmed areas by reed‐ and bush‐nesting passerines.     

Demography of grey partridges Perdix perdix in Poland in the years 1991–2004: reasons of population decline

Grey partridge Perdix perdix populations were monitored in the years 1991–2004 in ten agricultural areas (100–200 km² each) located in various regions of Poland. Spring density (call counts in March/April) and parameters describing reproductive success (counts of adult and young birds in coveys found in August) were estimated, and annual survival rate of adult birds was calculated. In the 1990s, the mean spring density of grey partridge in Poland showed a threefold decrease. In 1993 (the year of the highest mean density), from 4.6 pairs/km² to 20.0 pairs/km² were found in individual areas; whereas in 2004, there were from 0.4 pairs/km² to 8.3 pairs/km². The mean brood-production rate in individual years ranged from 29% to 49% (overall mean 36.8%), the chick-survival rate from 31% to 56% (43.1%), the young production from 1.6 to 2.8 young per adult (2.32 young/adult) and the annual survival rate of adult birds from 25% to 33% (28.3%). The population decrease in the 1990s was connected with the drop of reproductive success, including both the brood-production rate and the chick-survival rate, as well as with the decline of annual survival rate of adult birds. The decrease of brood-production rate and adult-survival rate probably resulted mainly from increased abundance of nest and incubating female predators (particularly foxes). Fluctuations in chick-survival rate were related to weather conditions, but also slight long-term decline was recorded, probably due to more intensive pesticide use.     

Grey Partridge Perdix perdix in the UK: recovery status,set‐aside and shooting

The Grey Partridge Perdix perdix is a European Species of Conservation Concern and a priority species under the UK Biodiversity Action Plan. The Game & Wildlife Conservation Trust (GWCT) launched a major programme to help partridge recovery in the UK, built on the GWCT’s Partridge Count Scheme (PCS) and including a demonstration site from 2002. We contrast the national picture of no population change since 1999 from BTO monitoring with a doubling of spring pair density on PCS sites. At the demonstration site, where set‐aside was used for habitat creation, Grey Partridge breeding density increased six‐fold, to 18 pairs/km², then fell back. The drop coincided with bad weather but also with the disappearance of rotational set‐aside when the set‐aside rate fell to zero, which halved the amount of brood‐rearing habitat. Non‐rotational set‐aside remained unchanged, as did the amount of nesting habitat that it provided. Grey Partridge density was significantly linked to rotational set‐aside, especially wild bird cover, but not to non‐rotational set‐aside. The demonstration project also showed that, with appropriate precautions, it was possible to shoot over 60% of Red‐legged Partridges Alectoris rufa while maintaining Grey Partridge losses below 5%. On PCS sites, the annual change in spring density in recent years differed in relation to neither shooting pressure nor intensity of Red‐legged Partridge releasing. Provision of brood‐rearing habitats and game cover increased with the latter, and probably counteracts the shooting losses of Grey Partridges on Red‐legged Partridge shoots when, as on PCS sites, active measures keep those losses below 20%. Targeted personal advice channelled through the PCS has been fundamental to these successes and must be expanded.     

Topographic spatial characterisation of grey seal Halichoerus grypus breeding habitat at a sub-seal size spatial grain

Expansion within breeding colonies may critically depend upon the availability of suitable breeding habitat. Here we use topographic modelling in a GIS to characterise suitable pupping habitat and accurately predict the pattern of colonisation in an expanding grey seal breeding colony – the Isle of May (Scotland). We use high resolution images from large format aerial photographs of the colony to generate sub‐metre accurate Digital Terrain Models (DTMs). GIS modelling with these DTMs provides topographic measures of elevation, slope and ease of access to sea and freshwater pools at a 2 m grid cell size. Seal locations during the 1994 breeding season, with sex‐age class, were also digitised from the same images. We examine how the physical attributes of cells (locations) with and without pups differ and identify areas suitable for pupping but remaining unoccupied during 1994. We predict patterns of future colonisation by characterising areas differentiated by the densities of pups within 5 m grid cells and identifying areas, both occupied or unoccupied, with a potential for increased future pupping densities. Our predictions were tested by examining pup distributions observed in the 1998 breeding season. Occupied sites were significantly closer to freshwater pools and access to the sea (p<0.001) than unoccupied sites suggesting that proximity to water may restrict colony expansion before all areas of suitably flat terrain are occupied. All pup density classes occurred in sites with similar slope values and distance to pools. However, higher pupping densities occurred closer to access points (p=0.014). Pup densities observed in 1998 revealed that our 1994 predictions were accurate (p<0.0001). Only 12% of 466 grid cells had higher densities in 1998 than predicted, of which 88% differed by only 1 pup. These incorrectly classified cells occurred at the expanding edge of the colony (in a more topographically homogenous area) and at the main access points from the sea (major traffic zones). These results demonstrate the value of the accurate quantification of topographic parameters at the appropriate spatial grain (in this case below the size of the individual) for use in habitat classification and predictions of habitat utilisation.