The cold northerly winds that saw out April persisted into 1 May but the sky cleared and the sun shone. May 2 proved to be very warm but things deteriorated again by 4 May as an Atlantic depression brought strong winds and rain. The period through the 4-6 May was characterised by some spells of warm sunshine, but also by the passage of some spectacular storms with lightning and torrential rain mixed in with a battering of hail on 4 May. The weather improved thereafter with high pressure holding sway and producing a fine and mainly sunny week from 9-18 May. The latter weekend in particular was very hot. But the ensuing week was much cooler as a high pressure system over Britain pulled in cool winds off the North Sea. In spite of long periods of sunshine, the air was cool and there were even some night frosts in the third week. But the month ended with a humid spell as weak fronts brought a change to westerly winds.
More summer migrants arrived on 1 May increasing the number of Sedge and Reed Warblers, Whitethroats and Blackcaps. However, the masses of hirundines (swallows and martins) held back by the cold weather departed en masse leaving screaming parties of Swifts to fill the aerial niche.
The storms on 4 May had a spectacular effect upon local bird recording leading to the location of the highlight of the year thus far. This was when not one but two Red-rumped Swallows arrived with a large influx of hirundines and Swifts. This dapper swallow has a generally Mediterranean distribution in Europe, seldom breeding far north even in France. However, it is an annual visitor to Britain. There are signs of a general increase in the number reaching Britain, but the arrival in spring 2004 has been unprecedented with upwards of 50 birds having been seen. The Waters’ Edge duo dropped down during a torrential rain shower in the afternoon of 4 May along with 100 Swallows, 60 House Martins and 400 Swifts. Such a spectacular arrival is usually associated with a mass movement of birds which have been held up on their northward migration by poor weather in southern Europe. In this case, the storms forced the birds down to feed. The weather turned suddenly cold, making insects hard to find except low over the water where there was an abundance of food. Although somewhat elusive, both of the Red-rumped Swallows were seen through to 6 May. After that, one was seen daily to 9 May when it was feeding low over the northern park before it drifted off south-west and was not seen again. These were the first Red-rumped Swallows to be recorded from the clay pits and formed only the second inland record for Lincolnshire.
On the same day which produced the Red-rumped Swallows, a singing Grasshopper Warbler was at the south end of Marsh Lane. A Common Buzzard flew south-west in a hail storm and a Short-eared Owl also flew west in the evening. All four species were first records for the year for the park.
By the end of the month, the reedbeds resounded to the song of Reed Warblers, with 45 males being counted. Ten male Sedge Warblers was a recent record total. A single Lesser Whitethroat sang for a mate without success, but four pairs of Blackcap and 1 pair of Willow Warblers were thought to be nesting. A Jay flew over the park on 9 and 10 May. And two male Treecreepers were singing in the south-west woodland on 2 May - a most unusual occurrence.
The Long-tailed Tits by Pasture Road fledged at least six bandit-masked juveniles on 22 May when a brood of Great Tits were also on the wing on the western park. Two Turtle Doves flying west on 9 May were the first of the spring, while a singing male on 13 May proved to be the only male recorded in the clay pits during the month. This is a sad situation for this once common summer visitor. On a similar a note, a single Cuckoo flying west on 9 May was also the only record of this species in the month. Better news concerned the arrival of two Spotted Flycatchers on 29 May. One male was even in brief song as they fed on the abundant insect supply around the Folly. This is now a rare and declining summer visitor, of which there have only been single records on the park in the last two years. If only they would settle to nest!
Waders were in short supply, but two Common Sandpipers present in the first week were heard singing and performed some display flights. A single bird was then seen intermittently through to 27 May raising the question as to whether a nesting attempt was underway. Up to three pairs of Ringed Plovers were present, but just one pair was nesting. Meanwhile, a pair of Little Ringed Plovers arrived in mid-month and also displayed frequently around their chosen territory on the new lagoon. Other species were few and far between, but the odd Lapwing fed on the northern ponds along with a few Dunlin. An Avocet landed briefly on the northern pond on 9 May, with a second bird in the air. And two attempted to drop onto the big pond later in the month, but diverted back onto the Humber. A flock of eight Oystercatchers roosted over the evening high tide on 19 May.
Ten broods of Mallard had hatched by the end of the month. This was fewer than in recent years. Other species were late, with the first brood of Pochard not being recorded until 27 May when eight newly hatched ducklings were in the eastern SSSI. The Mute Swans in this area hatched eight cygnets on 13 May and all of these survived to the end of the month. A pair of Great Crested Grebes remained on the park, but failed to nest. Little Grebe numbers were also down on recent seasons, with the first chick being seen on 18 May. An immature female Goldeneye was in the eastern SSSI from 15-19 May but this proved to be the only unusual species of waterfowl in the month.
A new species was added to the list of breeding birds on the park when a pair of Common Terns settled to incubate a clutch at the end of the month. Common terns have bred around the pits since 1993 but this is the first time that birds have bred on the park. Odd Bitterns were seen either flying over the park or dropping into the reedbeds to feed- a welcome sign of the continuing health of the local population of this nationally rare species. A singing Skylark over the meadows on 13 May was joined by a second bird on 27 May. Hopefully this species may nest if the meadows can be maintained in suitable condition.
Following the departure of the pair of Kestrels in April there were no further nesting attempts, but a young male moved into one of the nest boxes from 14 May and stayed for a few days. Typically for this date in the season he failed to attract a mate.
The annual butterfly list rose to twelve species during the month, with the appearance of:
- the first Orange Tip on 1 May
- Large White and Wall Brown on 18 May
- Common Blue on 25 May
- Small Copper on 27 May
- Red Admiral on 30 May.
It was good to see male Common Blues on 25 and 27 May along Marsh Lane, where the patch of bird’s-foot trefoil has proven attractive to this beautiful little insect. Orange Tips had a good spring with several individuals being recorded, but there were no sightings of Comma which is usually a typically early butterfly. The first Blue-tailed Damselflies emerged on 14 May with the first true dragonfly, a newly emerged Black-tailed Skimmer, on 29 May. The latter was three days earlier than the first emergence in 2003. One of the few moths recorded in the month was an Angle Shades found on 27 May.
A Stoat was seen on 13 May and the park Water Vole population appeared to be doing well with several sightings around the ponds.