Comparing call-playback to an observation-only method to survey Grey Partridge Perdix perdix on hill farms in northern England

Capsule: Call-playback in spring can be a practical method to survey Grey Partridges Perdix perdix in rough grasslands with abundant cover. However, further research is required to investigate movements and other responses to call-playback.

Aims: To compare call-playback with an observation-only method to survey Grey Partridges in rough grasslands with abundant cover, and to undertake a pilot study to consider whether bird behaviour conforms to point distance sampling assumptions.

Methods: Grey Partridges were surveyed using two separate methods: call-playback and observation-only, at 10 equally spaced points along 14 independent 4?km routes at 3 study sites in northern England. Surveys were undertaken at dawn and dusk in spring (March and April) and again in summer (August and September).

Results: In spring, call-playback registered at dusk fourfold and at dawn almost twice as many Grey Partridge encounters as the observation-only method. Methods did not differ in summer. In spring, using call-playback registered three times more encounters in rough grasslands with tall, dense cover than the observation-only method. Methods did not differ in summer. Grey Partridge encounter density estimates did not differ significantly between methods or seasons.

Conclusion: Using call-playback in spring increased the numbers of Grey Partridge encounters and can be a practical survey method, but further research is required to compare results against known populations and to investigate movements and other responses to call-playback, which may violate distance sampling assumptions.     

Long-term changes in chick survival rate and brood size in the Grey Partridge Perdix perdix in Poland

Data from 4801 Grey Partridge Perdix perdix broods collected in Poland during1987–2013 show that, over the 27 years of study, average brood sizes declined from 10.2 to 6.7 and chick survival fell from 57% to 34%. A probable cause of these trends was a 2.5 fold increase in the use of pesticides over the same time period.     

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.     

Managing the UK Grey Partridge Perdix perdix recovery: population change, reproduction, habitat and shooting

In 1995, the UK Government designated the Grey Partridge Perdix perdix as a priority species under its Biodiversity Action Plan (BAP). The Game Conservancy Trust (GCT), nominated as lead partner for the species, launched a programme to help Grey Partridge recovery by (1) raising awareness among the shooting and farming communities, (2) encouraging land managers and local BAP groups to conserve Partridges by setting numerical targets and offering feedback from counts on how to increase numbers, and (3) motivating by example by setting up a site demonstrating management techniques and the increase in Partridge abundance that ensues. Building on past research, we quantify the amount of habitat management required to achieve the BAP targets of halting the decline and achieving population recovery. Using three major GCT databases, (1) the National Gamebag Census, which collates data on shooting bags and gamebird releasing in the UK, (2) the Partridge Count Scheme, which monitors national Partridge density and reproduction, and (3) the Sussex Study, which monitors local Partridge population dynamics over 37 years, we emphasize the importance of good breeding success for increasing densities, review the evidence that management can be successful and evaluate the impact of shooting on Grey Partridge conservation.     

Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in France

We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long‐term decline in adult survival. We radiotagged and monitored daily from mid‐March to mid‐September 1009 females on ten contrasting study sites in 1995‐97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density‐dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat‐dependent predation.     

Managing the UK Grey Partridge Perdix perdix recovery: population change,reproduction, habitat and shooting

In 1995, the UK Government designated the Grey Partridge Perdix perdix as a priority species under its Biodiversity Action Plan (BAP). The Game Conservancy Trust (GCT), nominated as lead partner for the species, launched a programme to help Grey Partridge recovery by (1) raising awareness among the shooting and farming communities, (2) encouraging land managers and local BAP groups to conserve Partridges by setting numerical targets and offering feedback from counts on how to increase numbers, and (3) motivating by example by setting up a site demonstrating management techniques and the increase in Partridge abundance that ensues. Building on past research, we quantify the amount of habitat management required to achieve the BAP targets of halting the decline and achieving population recovery. Using three major GCT databases, (1) the National Gamebag Census, which collates data on shooting bags and gamebird releasing in the UK, (2) the Partridge Count Scheme, which monitors national Partridge density and reproduction, and (3) the Sussex Study, which monitors local Partridge population dynamics over 37 years, we emphasize the importance of good breeding success for increasing densities, review the evidence that management can be successful and evaluate the impact of shooting on Grey Partridge conservation.     

Sex‐ and age‐biased mortality in wild Grey Partridge Perdix perdix populations

Differing reproductive effort, individual qualities and local environmental conditions can lead to uneven mortality risk among individuals within populations and may result in survival differences according to age and sex. Identification of factors contributing to unequal operational sex ratios has been important for understanding population dynamics and conservation management. In this study, sex‐ and age‐specific mortality was estimated in three wild Grey Partridge populations from analysis of year‐round radiotracking data from 168 individuals. Survival days were counted in three periods defined individually for each bird: the pairing period (covey break‐up to laying of the first egg); the nesting period (between clutch initiation date and failure of the last nesting attempt, or the date when chicks were 14 days old); and the covey period (the end of the nesting period or joining a group until covey break‐up). Predation was the main cause of mortality. A significant effect of age on survival was found during the pairing period, when older individuals paired off faster and survived better. The highest mortality risk overall was found during the nesting period. Furthermore, significantly higher mortality of females was recorded during the nesting period, suggesting that greater investments in reproduction, behaviour at the nest or the quality of nesting habitats can decrease survival of females and cause a male‐skewed sex ratio. No significant effect of age or sex was found during the covey period, or for the year as a whole, but there was a significant difference in annual mortality rates between the three study populations. Our results confirm age‐ and sex‐specific variation of adult mortality in a ground‐nesting bird with biparental care during the annual cycle, documenting differing sensitivities of various population cohorts to predation.     

Effects of beta-carotene on adult immune condition and antibacterial activity in the eggs of the Grey Partridge, Perdix perdix

Carotenoids are important dietary constituents in birds. Their functions are numerous and complex, and breeding females are potentially faced with an optimal allocation of these resources between themselves and offspring. We conducted a dietary experiment (low and high supply of beta-carotene) to examine the effect of beta-carotene on health and immune response of 64 reproducing pairs of Grey Partridge (Perdix perdix L.) and on the quality of their eggs, as revealed by the measurement of biochemical components in yolk and albumen, the egg hatching rate and chick survival. We found a beneficial effect of beta-carotene on the erythrosedimentation rate and immune response of females (PHA reaction), while the diet did not significantly affect these variables in males. In both sexes, the plasma level of carotenoids was not related to the quantity of beta-carotene supplied. A higher quantity of beta-carotene in the diet did not induce a variation of egg nutrients (proteins and lipids), nor an increase of yolk beta-carotene concentration. We detected a higher concentration of lysozyme, an enzyme with antibacterial activity, in the albumen of eggs laid by females with a high supply of beta-carotene. These eggs showed higher hatching rates. The present study indicates that although carotenoid supplementation does not influence blood and yolk carotenoid levels, it results in better immune conditions of females, eventually translated into increased antibacterial activity of the eggs. The broad range of beneficial effects of carotenoids is discussed.     

Population dynamics of the Grey Partridge Perdix perdix 1793–1993: monitoring, modelling and management

The longest available bag record of Grey Partridges Perdix perdix in Great Britain (1793–1993) reveals a collapse of stocks after 1952 despite considerable annual variation. The annual fluctuations were attributable largely to annual variations in chick survival rate. The Game Conservancy Trust's National Game Census revealed that chick survival rates averaged 49% before the introduction of herbicides and 32% once their use became widespread. On a study area in Sussex, where spring density declined from around 21 pairs per km² in 1968 to under four pairs per km² in 1993, annual chick survival rates averaged 28% with no demonstrable trend. The annual over-winter "survival" rates in the area improved during 1968–1993, whereas brood production rates declined. Simulation modelling showed that a reduction in chick survival rate from 49% to 32% had little effect on spring stocks as long as nest predation was controlled but that stocks collapsed when nest predation control was relaxed. The effect of such a change in chick survival rate on population status was investigated by reference to 36 other studies in the literature. Amongst 20 studied populations which were stable, adjusting mean chick survival rates downwards produced demographic parameters characteristic of declining populations in all but two cases. Conversely, adjusting chick survival rates upwards for 16 declining populations made all but two stable. Diagnosing and remedying the causes of population change require a testable understanding of density-dependent factors and compensatory processes, best approached by a combination of monitoring, modelling and management.     

MHC Class IIB Exon 2 Polymorphism in the Grey Partridge (Perdix perdix) Is Shaped by Selection,Recombination and Gene Conversion

Among bird species, the most studied major histocompatibility complex (MHC) is the chicken MHC. Although the number of studies on MHC in free-ranging species is increasing, the knowledge on MHC variation in species closely related to chicken is required to understand the peculiarities of bird MHC evolution. Here we describe the variation of MHC class IIB (MHCIIB) exon 2 in a population of the Grey partridge (Perdix perdix), a species of high conservation concern throughout Europe and an emerging galliform model in studies of sexual selection. We found 12 alleles in 108 individuals, but in comparison to other birds surprisingly many sites show signatures of historical positive selection. Individuals displayed between two to four alleles both on genomic and complementary DNA, suggesting the presence of two functional MHCIIB loci. Recombination and gene conversion appear to be involved in generating MHCIIB diversity in the Grey partridge; two recombination breakpoints and several gene conversion events were detected. In phylogenetic analysis of galliform MHCIIB, the Grey partridge alleles do not cluster together, but are scattered through the tree instead. Thus, our results indicate that the Grey partridge MHCIIB is comparable to most other galliforms in terms of copy number and population polymorphism.     

Anti-predator function of not covering eggs in the initial phase of nesting in Grey Partridge Perdix perdix: a field experiment

ABSTRACT

Capsule: An experiment in the field supports the hypothesis that Grey Partridges Perdix perdix purposely expose their first laid eggs in order to test the predation risk at their nest site.

Aims: To test the hypothesis that female Grey Partridges leave first laid eggs uncovered to assess the predation risk at their chosen nesting site.

Methods: Four area-independent experiments with artificial nests were used. Predation risk was estimated by daily nest failure rate. Generalized linear mixed-effects models were used in statistical analysis.

Results: We found that Grey Partridge females could predict nest site safety. At nest sites where the first uncovered egg was depredated, there was a higher predation risk for the whole clutch.

Conclusion: Our data statistically support the hypothesis that leaving the first egg uncovered serves to provide a more conspicuous bait for potential predators and could be a female tactic for better recognizing predation risk at a nesting site. Thus, if the first uncovered egg is depredated, the female may start a new clutch elsewhere without wasting investment in the clutch at a site under high predation risk.     

Effects of beta-carotene supplementation on chick growth, immune status and behaviour in the grey partridge, Perdix perdix

Carotenoids are important for various functions during chick development. Since these pigments cannot be synthesized, they can be considered limited resources that the mother optimally allocates between herself and her offspring (maternal effect). Some studies have examined the effects of carotenoids on growth and immune function but little is known about their role in behaviour. In this study of the grey partridge, we conducted two supplementation experiments: (1) laying females were fed with beta-carotene enriched or impoverished diets; (2) chicks were fed directly with beta-carotene enriched or impoverished diets. We then evaluated the effects of this carotenoid on chick growth, immunocompetence and anti-predator behaviour (reactions to a raptor model). In the first experiment, the beta-carotene enriched diet given to mothers did not cause any difference in chick physiology. In the second experiment, beta-carotene supplementation of chicks had a significant beneficial effect on their growth and immune response, although their behavioural reactions did not differ in relation to the diet. Therefore, beta-carotene supplementation had beneficial effects on growth and immunocompetence only when directly supplied to chicks. The beneficial effect reported in other species for begging or pecking behaviours was not confirmed for the anti-predator behaviour of grey partridge chicks.     

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.     

Reproductive conditioning of the partridge (Perdix perdix) with GnRH and an increase in the photoperiod

Follicular growth and egg deposition were induced in the Grey Partridge (Perdix Perdix) after stimulation with Gn-RH and artificial light. The experiment was carried out from November to December 1983, during the short day period, and during the non egg laying period for this bird-sp. Two groups consisting of ten pairs of Grey Partridge each (female and male), received 3.8 mcg of Gn-RH (pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2) every 8 hours for 10 and 15 days, respectively. With interruption of the Gn-RH treatment we observed follicular regression. For this reason the birds were stimulated with artificial light daily from the 15th day of treatment until egg deposition. Fifty-five days after the start of the Gn-RH treatment the Grey Partridge laid eggs. Forty days of this period the birds were supplemented with artificial light. Twenty pairs of Grey Partridge were used as controls. Periodically two experimental female subjects (treated and control) were sacrificed to observe the development of ovary and oviducts.     

Habitat use, diet and body size of Heard Island weevils

Habitat use, diet and body-size variation are examined in weevils from Heard Island, with specific attention being given to the Ectemnorhinus viridis species complex. E. viridis shows marked altitudinal variation in body size and vestiture, but there are no consistent associations between body size and diet, nor are there consistent among-individual differences in conventional taxonomic characters. Thus, the status of E. viridis as a single, variable species is maintained. This species occurs from sea level to 600 m and it feeds on vascular plants and bryophytes. Canonopsis sericeus also feeds on bryophytes and vascular plants and occurs over a narrower altitudinal range. Palirhoeus eatoni is restricted to the surpralittoral zone where it feeds on marine algae and lichens. Bothrometopus brevis and B. gracilipes both feed on cryptogams, with the former species occurring from sea level to 450 m, and the latter from 50 to 550 m above sea level. In all species, males are smaller than females and there is a size cline such that populations from higher elevations are smaller than those at lower altitudes. This cline is the reverse of that found on the Prince Edward Islands which, unlike Heard Island, lie to the north of the Antarctic Polar Frontal Zone. This difference in body-size clines between weevils on the two island groups is ascribed to the shorter growing season on the colder Heard Island. The information presented here supports previous ideas regarding the evolution of the Ectemnorhinus-group of weevils on the South Indian Ocean Province Islands, although it suggests that subsequent tests of these hypotheses would profit from the inclusion of molecular systematic work.     

Vigilance and fitness in grey partridges Perdix perdix: the effects of group size and foraging-vigilance trade-offs on predation mortality

1. Vigilance increases fitness by improving predator detection but at the expense of increasing starvation risk. We related variation in vigilance among 122 radio-tagged overwintering grey partridges Perdix perdix (L.) across 20 independent farmland sites in England to predation risk (sparrowhawk Accipiter nisus L., kill rate), use of alternative antipredation behaviours (grouping and use of cover) and survival. 2. Vigilance was significantly higher when individuals fed in smaller groups and in taller vegetation. In the covey period (in early winter when partridges are in flocks), vigilance and use of taller vegetation was significantly higher at sites with higher sparrowhawk predation risk, but tall vegetation was used less by larger groups. Individuals were constrained in reducing individual vigilance by group size and habitat choice because maximum group size was determined by overall density in the area during the covey period and by the formation of pairs at the end of the winter (pair period), when there was also a significant twofold increase in the use of tall cover. 3. Over the whole winter individual survival was higher in larger groups and was lower in the pair period. However, when controlling for group size, mean survival decreased as vigilance increased in the covey period. This result, along with vigilance being higher at sites with increasing with raptor risk, suggests individual vigilance increases arose to reduce short-term predation risk from raptors but led to long-term fitness decreases probably because high individual vigilance increased starvation risk or indicated longer exposure to predation. The effect of raptors on survival was less when there were large groups in open habitats, where individual partridges can probably both detect predators and feed efficiently. 4. Our study suggests that increasing partridge density and modifying habitat to remove the need for high individual vigilance may decrease partridge mortality. It demonstrates the general principle that antipredation behaviours may reduce fitness long-term via their effects on the starvation-predation risk trade-off, even though they decrease predation risk short-term, and that it may be ecological constraints, such as poor habitat (that lead to an antipredation behaviour compromising foraging), that cause mortality, rather than the proximate effect of an antipredation behaviour such as vigilance.     

Habitat use, foraging ecology and diet of Turtle Doves Streptopelia turtur in Britain

Since 1968, Turtle Doves Streptopelia turtur in Britain have declined in number by 70% and in breeding range by at least 25%. This study was undertaken during the 1998–2000 breeding seasons at two sites in East Anglia to examine habitat use and foraging ecology. Home ranges of radiotagged Turtle Doves were 0.3–1130 ha in size and contained more woodland than expected from availability. Radiotagged birds undertook foraging trips of up to 10 km. Turtle Doves were recorded feeding primarily at 'man-made' sites (i.e. spilt grain, animal feed and grain stores) and were only infrequently recorded feeding at 'natural' sites. Diet analysis showed that wheat and rape seed averaged 61% of the seeds eaten by Turtle Doves. This contrasts with a study undertaken in Britain in the 1960s, when the seeds of wild plants (weeds) constituted over 90% of those eaten, with wheat and rape seeds making up only 5%. The current arrangements for set-aside and agri-environmental schemes provide a framework for the establishment and maintenance of weed-rich areas on farmland as a source of wild food.