Impact of habitat management on grey partridge populations: assessing wildlife cover using a multisite BACI experiment

Abstract

Summary 1.The grey partridge is a species of conservation concern, in common with many farmland birds. Its widespread decline in western Europe has been attributed to agricultural intensification. Attempts to restore populations have concentrated upon habitat management. In France, a mosaic of strips planted with maize-or kale-based mixtures is widely used to benefit the grey partridge on intensively cultivated farmlands. The rationale for planting these summer-to-winter cover strips is to increase the overwinter survival rate and hence breeding density. Although this policy is costly to apply, there is little information on its effectiveness. 2. We tested effectiveness of this management scheme as a practical way of improving or restoring partridge populations. We present data from a 6-year before-after controlimpact (BACI) experiment replicated across four study sites. We monitored partridge populations to estimate breeding density, reproductive success and overwinter mortality. 3. During the course of the study, no partridge population increase occurred on managed areas compared with control areas. Wildlife cover strips did not improve reproductive success but were associated with higher overwinter 'apparent mortality' rates. 4. Some field data suggested that there was a predation risk at cover strip-field edges. Cover strips may concentrate a number of species within small isolated areas and may act, under some circumstances, as an ecological trap for prey species such as the grey partridge. Due to these complex and unforeseen interactions, this habitat management measure proved unsuitable for partridge restoration. Synthesis and applications. This study has demonstrated the necessity of field experiments at a farm-scale to test the effectiveness of habitat management schemes. A priori assumptions based on smaller scale studies, even if they are supported by some field evidence, can be misleading because they fail to capture the emergent properties of larger scale systems. This study is a specific illustration of how the BACI approach is a powerful tool for addressing wildlife management problems at large spatial scales.

Ecological traps: current evidence and future directions

“…Adopting principles of BACI designs, coupled with studies of habitat selection will result in greater confidence that differences between sites are caused by traps. Bro et al [19] present a useful example of how monitoring fitness of grey partridges can be used to identify potential ecological traps resulting from replanting vegetation. All 'demonstrated' studies collected information about the attractiveness of traps and their fitness costs (figure 4: T. att and T. fit), which is required to meet the three criteria for documenting a trap [7].…”

Autumn–winter diet of Grey PartridgesPerdix perdixin winter crops, stubble fields and fallows

“…However, these features also have positive effects on the presence of predators. In this context, both field edges, stubble fields or places of artificial feeding may act as ecological traps (Bro et al 2004, Reid et al 2007, Rantanen et al 2010. Hence, winter crops could be considered as an important land-cover type for Grey Partridges in the autumn-winter period which assure both 'safe' roosting and suitable feeding sites.…”

Ecological restoration of farmland: progress and prospects

“…The loss of habitat from agricultural expansion is generally the main reason suggested, but the evidence can be weak if it is based on anecdotal observations, unpublished data or 'grey' literature such as annual reports rather than empirical evidence in refereed scientific publications. Nevertheless, these lists are regarded as an extremely Bro et al (2004) and Evans (2004) indicator of habitat quality (2004) a Also regarded as pest species because they vector bovine tuberculosis to cattle and deer in New Zealand (Byrom 2002). valuable tool for conservation planning, management, monitoring and decision making (Rodrigues et al 2006). However, what is the relevance of these lists for farmland ecological restoration?…”

“…These guidelines and other generic principles (Samways 2007) have been supported by conceptual frameworks and practical methods for developing ecological restoration programmes and evaluating ecological risk, which are generally not specific to farmland but nevertheless provide a useful starting point for this particular land use type (Hobbs & Norton 1996;Hobbs & Harris 2001;Parkes et al 2003;Oliver 2004;Cramer & Hobbs 2005). It is generally accepted that (2003) 3 increase the availability of non-cultivated land adjacent to fields which provide natural nesting and over-wintering sites (physical shelter and shelter from predation) and primary or alternative food sources, either by deliberately sown noncrop plants (beetle banks, cover strips, floral mixtures and hedgerows), natural regeneration (set-aside land without pesticides or conservation headlands with selective pesticides, uncropped field margins and grassy margins) or repair of existing vegetation Thomas et al (1991;; Bro et al (2004) and Pywell et al (2004Pywell et al ( , 2005b 4 increasing the number of fields by reducing the size of each Holland et al practical guidelines for restoration must be based on sound theoretical and empirical foundations, yet be easily integrated into agricultural and horticultural practice (Summerville et al 2005). Yet in this context, Hobbs & Harris (2001) made two salient remarks: firstly, practitioners now desire a stronger ecological foundation for developing and implementing restoration projects; and secondly, it has become apparent that the assumptions underlying many restoration projects are based on outdated concepts of how ecological systems function, such as on the stability of ecosystems and the ability of them to return to equilibrium states following disturbance.…”