The table, compiled from statistics published in the Northamptonshire Bird Report, shows the times of the year when migratory birds were present in Northamptonshire for the twenty-eight years since the Report was first published. The relevance of future sightings can thus be quickly seen. Not all migrants are represented because a proportion of some species such as Tufted Duck Aythya fuligula and Common Starling Sturnus vulgaris is present throughout the year. Occurrences of others, like the Great Cormorant Phalacrocorax carbo, show no set pattern and still others like the phalaropes and skuas are too rare to warrant useful inclusion in the table.
Each month is divided into three sections; the first section represents records for the 1st-10th inclusive, the second section for the 11th-20th and the third for the 21st to the end of the month. The values, to separate the four different rates of occurrence, do on the surface appear somewhat arbitrary. These values have been calculated so that a direct relationship can be made with the chart in the 1984 Bird Report which relates to the fifteen years from 1969-1983.
The table represents the number of records of a species in a period rather than the total number of individuals, because instances such as the 77 Black-tailed Godwit Limosa limosa at Ditchford Gravel Pits on 27-04-1980 would clearly unbalance any pattern in the records of that species which may be apparent over the twenty year period.
A key to the symbols is given in the Table. Sporadic breeders and those with small breeding populations were not considered to warrant the 'common' rating despite being present in 'full force'.
During the course of compiling the information, several trends relating to individual species surfaced which could not be indicated in the Table. There was a substantial increase in the number of records during the period, the main reason being the increase in the number of observers. By taking these increases into account and calculating the expected increase for each species, it is possible to identify trends which are worth noting and comment on their possible causes.
There were two summer migrants to Northamptonshire which showed a distinct increase over the twenty-five year period. Indeed, one, the Great Ringed Plover Charadrius hiaticula, may even attain a different status if it continues to increase at its current rate. It is now present annually at several sites and this number will surely rise with the planned expansion of the gravel workings in the Nene Valley. The significant feature of this species is its continually expanding stay in Northamptonshire, which, at its present rate, might promote it to resident status. The number of Hobby Falco subbuteo records has increased significantly and from being an uncommon passage migrant in 1969 it is now a regular breeder. The presence of Hobby Falco subbuteo breeding in Northamptonshire is in line with this species' continuing expansion in Britain.
A summer migrant to show a completely different trend is the European Nightjar Caprimulgus europaeus. Its distribution and numbers have continually fluctuated but finally the European Nightjar Caprimulgus europaeus status as a rare breeder has changed to that of a rare passage migrant. There have been just a handful of records in the last ten years although surprisingly the bird on 05-05-1987 was the earliest on record.
During the first ten year period there were only twenty records of Black-legged Kittiwake Rissa tridactyla and in the three years, 1970,71 and 72, none were seen at all. This is in sharp contrast to the last fifteen year period when there were more than two hundred records, which, considering its fairly static status in Britain, must be due to better observer awareness.
Similarly, this same awareness no doubt contributed to the rapid increase in Arctic Tern Sterna paradisaea records in spring; there were seven spring records in the first five years and more than one hundred records in the last five years.
The records of Rufous Nightingale Luscinia megarhynchos are obviously not a true indication of the presence of this species in the County. Considering the extreme difficulty in recording the Rufous Nightingale Luscinia megarhynchos after its initial period of high activity, the low numbers of reports is hardly surprising. It is however the only species where there is a marked difference between the expected and recorded levels of presence. Even in the last five years there was only one record later than the first third of July and that was 23-09-1986; the latest report on record.