ANALISIS Y DISCUSIÓN

INTRODUCTION

Johnston (1923) reported nest counts of rookeries in parts of Fife but only mentioned the existence (in 1921) of five in N.E. Fife. All of these were located in the vicinity of the town of

Cupar. Only two of them (those at Tarvit and Lochmalony) existed for certain twenty-four years later when the national survey of rookeries was carried out. Between these dates (1921 and 1945) no census of rookeries took place in N.E. Fife but Grierson (1962) referred to four rookeries in the area which existed in 1960. These were at Earlshall ("over 500 pairs"), Guardbridge, Tayport and Leuchars. The first two of these were in existence in 1945 and continue to be so up to the present, while the other two are now extinct.

The returns for the 1945 survey were made by L.J. Rintoul and E.V. Baxter. These two workers provided with the returns much background information on Fife rookeries, including the age of some of them. Of the nine rookeries which Rintoul and Baxter reported as being less than 10 years old in 1945 seven are now extinct; both rookeries which were between 10 and 20 years old in 1945 are now extinct; of the three which were between 20 and 50 years old one is

extinct; and of the seven which were greater than 50 years old five I are now extinct. In addition, of three rookeries which were

described as "many years old" two are extinct and of seven described as "old" four are extinct. Most of the rookeries which were counts in the 1975 national survey were still in existence in 1978 and later.

A total of 14,466 nests in 83 rookeries was counted in N.E. Fife in 1945. In 1975 the corresponding figures were 3,452 nests in

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77 rookeries. Ostensibly, this represents a 76.14% decrease in the number of breeding rooks in the area over a thirty year period.

However, many problems are associated with the counting of rook nests, and these may be especially significant with regard to

national surveys. The most obvious problem is that when many people are involved in the surveying of a large area many rookeries may not be counted at all. For anything like complete coverage to be

attained it is preferable that the survey be done by people (or even

one person) who know the area well in terms of the location of *| rookeries. Even when an area is well-known one can never be sure if

all rookery sites have been recorded. In 1945 Fife was, as

mentioned, censused by Rintoul and Baxter. These were arguably the most distinguished ornithologists in Scotland at the time, and their writings give the impression of great attention to detail. For these reasons the 1945 rookeries census in Fife was probably as near

complete as one could hope for. The 1975 census in N.E. Fife, on the other hand, was carried out by almost a dozen people. This resulted in some rookeries being missed so the figure of 3,452 nests counted in that year must only be taken as a very rough approximation. The number of rookeries omitted was unlikely to have been so great as to disguise the fact that there had been a large decrease in the rook population since 1945.

METHODS

For convenience, each rookery recorded in N.E. Fife in the 1975 national rookeries survey was given a reference number. This consists of two digits followed by a / followed by another two digits. The first two two digits indicate the Ordnance Survey 1:25

000 NO sheet on which the rookery is located. The second pair of digits identify the rookery as number 1, 2, 3, etc. and these were

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applied randomly. Thus the rookery at Crail Church (Grid Reference NO 614080) was given the reference number 60/03, indicating that it was the third rookery to be assigned a reference number in sheet NO 60. Any subsequent rookeries discovered in the area covered by this sheet would be assigned the reference numbers 60/04, then 60/05, and so on.

Censuses of the N.E. Fife rookeries were made in 1977, 1978 and 1979. Those in 1977 and 1979 were sample censuses, only the nests in some rookeries being counted. In 1978 ah almost complete census was made. In addition, complete (or, again, almost complete) censuses were carried out in 1980 and in 1983 but the results of these, while they may occasionally be alluded to, for the most part lie outwith the scope of the present study.

The method of estimating the size of the breeding

population of rooks in a defined area is fairly straightforward, but there are several sources of error of which the researcher must be aware in order that the results obtained be as accurate as possible.

Errors may be of many kinds. Perhaps the most serious type is that of not counting the nests in a rookery at all. This may happen because the locations of all rookeries in the study area are not known. Searches for unrecorded rookeries, while they may be intensive, will probably never result in all rookeries being discovered in a single season. To overcome this problem one must draw on local knowledge, but there is no substitute for getting to know the area thoroughly oneself and this takes years. Although as complete coverage of the study area as possible was attempted in the 1978 survey several rookeries which almost certainly existed were

missed. A related problem here is that "rookeries" containing only a Ç: single rook nest are even more difficult to locate. (These are

referred to as being rookeries in the present study). Such nests

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might be very transitory, being occupied for only one season, and so A

pass undiscovered. If they form the genesis for new colonies then these may be discovered in subsequent years but it remains that the survey results for one year will be inaccurate. This inaccuracy is

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