Factors Affecting Populations of Farmland Birds. a Study of Data Collected Between 1993 and 1998 At
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MINISTRY OF AGRICULTURE, FISHERIES AND FOOD Date project completed: -. Research and Development 28/02/1999 Final Project Report BDml1 (Not to be used for LINK projects) 1. (a) MAFF Project Code IBD0911 (b) Project Title FACTORS AFFECTING POPULATIONS OF FARMLAND BIRDS - A STUDY OF DATA COLLECTED BETWEEN 1993 Ai'ill 1998 AT ADAS DRAYTON (c) MAFF Project Officer I DR P COSTIGAN (d) Name and address ADAS CONSULTING LTD of contractor OXFORD SPIRES BUSINESS PARK THE BOULEYARD KIDLINGTON, OXON Pastcade OX5 1NZ (e) Contractor's Project Officer I_M_R_C_P_B_R_lT_T _ (f) Project start date 101/iO/l99R Project end date 13 1/01/1999 (g) Final year costs: approved expenditure I £9,663 actual expenditure (h) Total project costs 1total staff input: approved project expenditure I £9,663 actual project expenditure 'approved staff input 'actual staff input (i) Date report sent to MAFF 124/03/1999------ Ul Is there any Intellectual Property ari~ing from this project? 'staff years of direct science effort CSG 13 (1/97) 1 Ilij!!!.:I~Jlll~ilwl!II~~ijlllI11~ll!llll~g,~!lill~11l§l!ll~~,el!!;!!!~~II.;~I:'!~~!,!tgll!lllill111111~l!lill~11~IIIII!li!Jl[IIIIIIIII'I~ 2. Please list the scientific objectives as set out in CSG 7 (ROAME B). If necessary these can be expressed in an abbreviated form. Indicate where amendments have been agreed with the MAFF Project Officer, giving the date of amendment. 01 To collate Common Birds Census and farm management data from the ADAS Drayton ECN site. 02 To statistically analyse bird population data, to detennine the habitat preferences of skylarks and yellowhammers and examine other possible causes of spatial and temporal variation. 03 To compare Drayton ECN birds' data with those from lACR Rotharnsted and other appropriate lowland ECN sites. 04 To evaluate the short-tenn effects ofagricultural practices on populations ofskylarks and yellowhammers and provide recommendations for future research. 3. List the primary milestones for the final year. It is the responsibility of the contractor to check fully that ALL primary milestones have been met and to provide a detailed explanation if this has not proved possible Milestones Target Milestones met? date Number Title in full on time 01/01 Complete collation ofADAS Dra)10n birds (CBC) 10/11/1998 YES YES data 01102 Complete collation of ADAS Drayton farm 10/11/1998 YES YES management data 02/01 Complcte analysis of ADAS Drayton data. 04/12/1998 YES NO 04/01 Complete project report for I\'lAFF 31/01/1999 YES NO If any milestones have not been met in the final year, an explanation should be included in Section 5. 111111111~'I!llllil!;IIIIIIIII~III~llii!IIl:!!i~lil!!I'1111~1~1\liiljllllllil!;!':i!lli;lllg!I~liil\llllI11~i1111!llill1!1111~llill!I':I:lllliili!I;llll!II'ilillllil1iliiililllil~1 4. I declare that the information I have given in this report is correct to the best of my knowledge and belief. I understand that the information contained in this form may be held on a computer system. Signature I 1 Date 1---- Name 1 Christopher P Britt I Position in Organistation ILS_e_n_io_r_R_e_se_a_rc_h_C_o_n_Sl_ll_lan_t _ CSG 13 (1/97) 2 , • This study examined population changes/activity levels in two farmland bird species (skylark and yellowhammer) over a six year period, at ADAS Drayton - a lowland mixed farm in south Warwickshire - using registrations data from annual Common Birds Censuses, undertaken as part of the UK Environmental Change Network (ECN) project. Results were also compared with data obtained from a second lowland agricultural ECN site, at the Institute of Arable Crops Research at Rothamsted, in Hertfordshire. National populations of both species have declined in recent years and this study, as well as determining whether similar declines occurred at Drayton, also attempted to determine the effects of cropping and the management of non-cropped areas on bird activity. Carabid beetle activity was also monitored each year (within the ECN project), and the numbers of beetles captured annually were compared with skylark and yellowhammer registrations, to examine any possible correlations between these groups. The number of breeding territories of skylarks declined steadily over the period of the study. The number of registrations per hectare, however, did not differ significantly between years but did indicate major differences in the attraction of various crops to skylarks. Rotational set-aside, where vegetation was allowed to naturally regenerate, was very attractive in comparison with other crops. The lowest numbers of registrations were recorded on intensively managed grass fields. The results generally agree with fmdings from other studies, and suggest that the sparser vegetation present in rotational set-aside allows skylarks to forage and nest successfully, whereas the denser, more disturbed intensively managed grassland does not. The invertebrate diet of these birds is also likely to be present in greater amounts on set-aside land. The correlation between Carabid beetle numbers trapped in field boundaries and skylark registrations was poor. This probably reflects the fact that the skylark is reliant on the open field habitat and that invertebrate populations, as measured by Carabid beetle numbers in field boundaries, do not allow valid comparisons between years to be made. Yellowhammer populations were affected by the management of cropped and uncropped areas of farmland. Comparisons of various cropping combinations occurring each side of a field boundary indicated a positive effect for rotational set-aside and a negative effect for intensively managed grassland. Although the type of hedge forming the boundary, in terms of its density, did not affect the number of registrations significantly the presence of a ditch and an unmanaged grassy area more than 1. 5 metres wide adjacent to the crop did result in significantly higher numbers of registrations. No grass fields contained a ditch with an unmanaged grass strip of greater than 1.5 metres wide and therefore no valid comparisons between effects offield margin type on the two major cropping regimes (arable vs. grassland) could be made. Yellowhammer population declines occurred when Carabid beetle numbers in field margins fell, indicating that these beetles may be a good indicator of prey availability for yellowhammers, and that uncropped field margins are an important habitat for foraging yellowhammers. The beneficial effects of field margin management for wildlife in arable situations has been examined in a number of studies. There is an urgent need to ascertain whether similar benefits would be obtained from alternative management of intensively managed grass field margins, especially in the western half of the country, where the intensity of grassland management has increased most, and is likely to have had the greatest affect on species such as the yellowhammer. CSG 13 (1/97) 3 A study offarmland bird populations: an analysis ofskylark (Alauda arvensis) and yellowhammer (Emberiza citrinel/a) registrations data from common birds censuses at ADAS Drayton, 1993-98 INTRODUCTION The populations of a number of fannland bird species have declined in recent years. These declines have coincided with a period of increased intensification of agricultural production. TI,e Environmental Change Network (ECN) project is carried out on a number of terrestrial and freshwater sites throughout Britain. It is a long-tenn integrated monitoring progran>me designed to identify and improve the understanding of the causes of environmental change. The site at ADAS Drayton is sponsored by the Ministry of Agriculture, Fisheries and Food (MAFF). A wide range of physical, chemical and biological variables are measured by the ECN. One of the variables which has been measured since 1993 at Drayton is the population of breeding birds. During this time changes in populations of particular species have been recorded and the changes agree, in general, with those detennined in the national Common Birds Census (CBC) carried out by the British Trust for Ornithology (BTO). Another variable being measured is the number and species of Carabid beetles present at the site. Changes in the population levels of these insects have also been noted during the period 1993 to 1998. The site is one on which agricultural research has been carried out for many years and, therefore, detailed infonnation about the agricultural management of the site is available, enabling populations changes to be measured against changes in management practices. Skylarks (Alauda arvensis) and yellowhan>mers (Emberiza cilrine/la) are two of the species of farmland bird which have experienced large population declines in recent years and have been the subject of much recent research (e.g. Grynderup Poulson el al., 1998; Wilson el al., 1997; Kyrkos el al., 1998; Sparks el al., 1996; Green el al., 1994). Nationally, skylark populations have been recorded as declining by almost 60% since 1970 in BTO studies. Yellowhammer populations were relatively stable during the late 1960's and 1970's, while other farmland birds declined; but populations started to decrease in the late 1980's (Bradbury el aI., in press), with a rapid increase in the rate of decline in recent years. Currently, yellowhan>mer populations are declining by around 10% per year (Bradbury el aI., in press). The two species occupy different areas of farmland. Skylarks live in more open habitats, nesting on the ground amongst crops. Yellowhan>mers, on the other hand, nest along field boundaries, either on the ground, in ditches or grassy margins, or in shrubby growth such as hedges. It feeds mainly in nearby adjacent habitats. Various possible causes of decline in British yellowhan>mer populations have been suggestcd by previous authors (Morris el al., in press). These include: I. The shift, in western Britain, toward grass monocultures, which harbour smaller invertebrate prey populations and invertebrate diversity (e.g. in the Orthoptera and Staphylinidae) 2. A resultant reduction in cereal grain availability.