Abstract1. Across Europe, farmland bird populations have continued to decline since the 1970s owing to the intensification of farming practices. Studies of such declines have tended to focus specifically on either the impacts of habitats (nesting and foraging), nest predators or prey availability on bird demographics. The study presented here provides new insights into the relative effects of each of these factors on yellowhammer nest survival. The yellowhammer was selected for this study as it is a UK Red‐Listed bird species whose population is in decline across much of Europe.2. We use a long‐term dataset of 147 nests, monitored between 1995 and 2007, to provide an insight into how yellowhammer nest survival is influenced by nesting habitat (nest concealment and nest height), foraging habitats (habitat coverage within 100 m of nests), the removal of nest predators (magpiePicaabundance as an inverse measure of avian predator removal through gamekeeping) and food availability (measured with a D‐vac invertebrate suction sampler).3. Our results indicated that yellowhammer hatching success was negatively related to the coverage of spring agri‐environment scheme habitats, a group which represents invertebrate‐rich agri‐environment habitats, but hatching success increased with nest height. Fledging success was positively related to the coverage of the seed‐rich habitat wild bird seed mixture. The farm‐level abundance of yellowhammer chick‐food invertebrates declined over the study period.4. Our results highlight the importance of simultaneously considering multiple agents that shape avian breeding success, that is their ability to produce offspring, to inform conservation management. Our key finding for land managers relates to the positive relationship between the proportion of seed rich foraging habitat within the yellowhammer's average foraging range and yellowhammer fledging success, which shows that a habitat intended primarily to provide winter food resources is also important to breeding birds. Chick food abundance in this habitat was, however, similar to broadleaf and cereal crops. We recommend that this habitat should be provided near to potential yellowhammer nesting sites and adjacent to invertebrate‐rich agri‐environment scheme habitats such as beetle banks and conservation headlands to further boost invertebrate resources for a declining farmland bird.

There is global concern that invertebrate populations are declining rapidly, particularly in agricultural habitats. Declines have been attributed to the intensification of farming systems, with many studies focussing on a lack of semi-natural habitat in the landscape and the use of insecticides. However, within-field arable weeds are also an important driver of invertebrate abundance and the ecosystem services to which they contribute. This study focuses on the role of arable weeds in supporting invertebrate populations and selected ecosystem services they deliver., using winter wheat as a case study. Weed-invertebrate relationships were investigated across seven studies of winter-sown wheat spanning 18 years. Both phytophagous and predatory invertebrates responded to weed cover but to different degrees. Phytophages showed a stronger positive relationship with weed cover than the predators, because they rely on the resources provided by the weeds whereas predatory species response is likely to be mediated by their prey. Farmland bird chick-food indices were positively related to both broadleaf and grass cover in cropped fields, indicating that increased weed cover can provide increased invertebrate food for birds in winter wheat. Despite this potential, there were insufficient invertebrate food resources for birds in the majority of wheat fields sampled. Weed diversity did not play a significant role in moderating the relationships between weeds and invertebrate abundance, however this may be a function of the low weed diversity in modern winter wheat fields. In this study the weed species most frequently shown to predict the invertebrate community were: Poa annua, Stellaria media, Fumaria officinalis, Sinapis arvensis, Senecio vulgaris, Persicaria lapathifolia, Sonchus spp., Matricaria discoidea, Persicaria maculosa, Agrostis spp., Lamium purpureum, Lamium album, Veronica spp., Atriplex spp., Myosotis spp. and Anagallis arvensis. We conclude that even in an intensively grown cereal, arable weeds can play an important role in maintaining and restoring invertebrate populations, that 10% weed cover is needed to fulfill the potential and that a successful outcome will be driven by the presence of weed species that support invertebrates that provide ecosystem services.

It is widely recognized that landscape factors affect the biological control of weed seeds and insect pests in arable crops, but landscape effects have been found to be inconsistent between studies. Here, we compare six different types of sentinels (surrogate prey that was either live insects or seeds) to measure the effects of semi-natural habitats at field to landscape scales on levels of biological control in winter wheat in the UK. Sentinels were located in fields adjacent to three boundary types: grassy margin, hedgerows or woodland to study the local scale effects and in landscapes of varying heterogeneity in study areas of 1-km radius. Overall, mean levels of predation were higher for most insect prey (60.8%) located on the ground compared to the crop (12.2%) and was lower for seeds (5.8%). Predation of sentinels on the ground was attributed to generalist predators. Semi-natural habitats had both positive and negative effects at field and landscape scales, but the response varied with the sentinel type. Herbaceous linear semi-natural habitats had positive effects at local scales for Calliphora vomitoria and Sitobion avenae sentinels and provide evidence that farmers can introduce linear herbaceous features to benefit biological control. In contrast, our distance-weighted kernel models identified a positive relationship between woody habitats and the predation of C. vomitoria and Chenopodium album. Natural aphid infestations were lower in landscapes with more semi-natural habitat. Synthesis and applications. Sentinels may be sensitive enough to detect variation in levels of biological control influenced by semi-natural habitats, but this study confirms that landscape effects differ for different types of sentinel prey. This implies that it may not be possible to categorize landscapes as pest suppressive using a single sentinel type. Future studies should therefore consider using multiple sentinels to give a better perspective on predation intensity. The resulting recommendations for farm management include planting woodland adjacent wheat fields infested with seed predators and positioning herbaceous linear habitats adjacent wheat fields infested with Sitobion avenae, particularly if fields are bordered by woody liner habitats due to their association with decreased S. avenae predation.

Capsule The body condition of nestling Yellowhammers was negatively correlated with the amount of cereal grain in the diet. This supports the hypothesis that cereal grain is an inferior nestling food relative to invertebrates. Cereal grain is frequently provisioned to nestlings in a range of bunting species breeding on farmland, suggesting that invertebrates may be limiting in these habitats.

The niche hypothesis predicts that some introduced species establish and spread successfully because their new environment provides expanded niche opportunities compared with their native environments. By investigating nestling survival, growth and body condition in relation to diet composition and prey abundance, we tested the prediction that the success of Yellowhammers Emberiza citrinella in New Zealand could be explained by the availability of better quality food resources in its introduced range compared with its native range. We found that Yellowhammer nestlings in New Zealand were larger and heavier than those in Britain, but that nestling survival and body condition did not differ between countries. The preferred prey items, which had some influence on nestling development and survival, were more prevalent in the diet of nestlings in New Zealand, suggesting that nestlings in the introduced range had a superior quality diet. However, there was little evidence to support the prediction that the preferred prey were more abundant in the introduced range, implying that some other factor such as prey accessibility or adult fitness may account for the differences in diet between countries.