Migrant Dates

One of the interesting aspects of birding in Buckinghamshire is the arrival and departure of migrant species (such as Cuckoo, Swallows, etc). Questions are often asked as to what is the earliest arrival date, or what is a typical arrival date for a specific species. This post answers many of these questions.

The data below contains data on the various migrant birds species found in Buckinghamshire and has been extracted from Annual Reports for the county from 1971 until 2019 . It includes Summer visitors, Winter visitors and passage migrants.

This date was compiled by Jim Rose and Graham Smith.

Please bear in mind the following points :-

• The average dates given are that of the earliest records received and not the typical arrival date which is obviously somewhat later.   The opposite of course applies to average late dates.
• Some species that are normally regarded as UK residents (e.g.  Ringed Plover) can be treated as summer visitors to Bucks as there is a clear break in records during the winter months.
• Some species that are regarded as summer visitors to the UK, may in fact be treated as migrant species in Bucks (e.g.  Wheatear), as it is possible to separate the spring passage from the return passage. Hence there are two sets of tables for these species (see Spring and Autumn Migrants).
• You may find that there are some species missing from the tables that you might have expected to see.  This may be due to the back that some species that are normally regarded as say a summer visitor do turn up during other months making it difficult to determine arrival and departure dates (e.g. Blackcap).
• Where the occasional exceptional record occurs (e.g. where a normal summer visitor is recorded over wintering) that record is ignored from the average date calculation and from the earliest/latest ever data.  This is indicated against that species in the table.  Similarly in years where wintering birds stay on to breed, the dates for those years have been ignored (e.g. Goosander).
• Additional years data will be added on the publication of the Buckinghamshire Annual Bird Report.
• Red Italics means that data is inconclusive due to some out of season records or lack of data

_____________________________________________

Below is one example of how migrant arrival dates have changed over the years. It appears that Swallows now arrive up to ten days earlier than previously.