Typical April showers permeated the first days of the month, but in the sunny spells it was unusually warm, reaching 15ºC. The warmer days were cut short by 4 April as a cold north-west air-stream brought heavy showers, some with hail. And this cold snap lasted through to 9 April. The weather eventually warmed up by 12 April with a beautiful sunny day occurring on the thirteenth of the month. Cooler temperatures prevailed to the weekend when 24 hours of torrential rain washed out many early nests. Thereafter things could only improve. But the sudden change to Mediterranean conditions on 23 April was almost unprecedented. Typical daytime temperatures reached the mid 20s Celsius and night-time lows only fell to the mid teens. Insects abounded for a few days. Cold northerlies ended the month with three days of poor weather terminating the heat wave and bringing a distinctly wintery feel to the park.
Highlight of the month and the year so far was the appearance of a superb drake Lesser Scaup on the northern ponds between 28-30 April. This Nearctic duck was only added to the British list in 1987. But there has been a steady increase in the number of birds occurring on this side of the Atlantic, with a total of 53 having been recorded up to the end of 2002. There has been one previous occurrence on the clay pits in February 1995, which was also the first record for Lincolnshire, but this is the first record for the Country Park.
A flush of early summer migrants arrived on 3 April with two Swallows passing west while the first singing Willow Warbler and Blackcap graced the local scrub. In spite of the cold winds, hirundines increased over ensuing days with up to 30 Sand Martins and the first House Martins passing through on 4 April. This is the earliest ever date for House Martin in the clay pits, which is somewhat surprising given the prevailing weather conditions. Chiffchaffs also increased, with five to six singing males in evidence as new birds battled with established locals for prime breeding sites in the south-east of the park. The first Willow Warbler struggled into song on 3 April but it was the ninth of the month before a second bird arrived. There were still only four male Willow Warblers by 13 April with the first major influx occurring on 26 April when 14 were present.
Other migrant arrivals included Sedge and Reed Warblers on 24 April. Both species quickly increased as more birds arrived in the heat wave over the 25-27 April. By the end of the month, there were already six singing Sedge and at least 14 Reed Warblers. A male Lesser Whitethroat set up a territory on the east side of the park while a Whitethroat typically sang from the scrub by the sewage works, both birds arriving on 24 April. A Cuckoo was heard on 23 April but this proved to be a lone occurrence as there were no more records by the end of the month.
The first Common Tern arrived on 24 April. On the same day, an early Swift was over the eastern site of special scientific interest (SSSI). But much more unusual was a marked arrival of Swifts on 26 April when 18 were screaming over the park. This was a good week earlier than in most years, no doubt a result of the very warm weather. Yellow Wagtails passed over from 24 April but none landed in spite of the seemingly suitable looking wet grassland on the northern park. During the cold weather at the month end, hirundines and Swifts were concentrated over the ponds with peaks of 40 Swallows, 60 House Martins, 20 Sand Martin and 50 Swifts. The northerly also gave rise to a passage of Arctic Terns and a flock of 13 flew north over the park on 30 April.
Passage of emigrating finches was also in evidence with Siskin and a party of 14 Lesser Redpolls arriving on site. But pride of place went to a superb summer plumaged cock Brambling. This truly dapper finch is a breeding bird of the northern coniferous woodlands in Scandinavia but winters in variable numbers in Britain. Returning birds are sometimes held up on the east coast in spring by easterly winds. They then resort to feeding on insects which they often catch in flight as opposed to their usual winter diet of seeds and beech mast.
The Redshank roost on the northern park was still much in evidence in the early mornings during the first week. There was a peak of 124 birds being recorded on 3 April but other waders were few and far between. A single male Little Ringed Plover lingered through the first week and was joined by a female on 13 April but in spite of showing interest in the shingle area they departed by mid-month. Up to seven Ringed Plover were seen in the first week but thereafter a single pair settled to attempt to nest. Frequent disturbance of their chosen site on the northern footpath meant that nesting attempts were thwarted. Two Common Sandpipers arrived on 23 April, with one lingering to 24 April. And three Dunlin on 27 April were the first for many weeks. Other species noted in 2003 were lacking this year, including Avocet, Oystercatcher and Green Sandpiper.
The male Great Spotted Woodpecker continued to drum daily on his chosen trees around the south-west of the park to the middle of the month, by which time the two pairs of Mistle Thrush and one pair of Song Thrush were feeding young.
Waterfowl got down to the serious business of nesting in earnest. Evidence of the early start by some of the Greylag Geese was the sight of two broods of five and six goslings on the northern park from 12 April. There were six broods evident by 26 April with 26 young. Up to eight Teal lingered to mid month, along with a pair of Shoveler. There were four female Pochard but Tufted Duck numbers jumped to 32 in the second week. The first brood of Mallard, eight, were on the Middle Lagoon on 26 April. A second brood followed the next day. Six pairs of Little Grebes were established in their usual areas, but much rarer was the grunting Bittern present in the western SSSI from 24-26 April.
The first really warm day to tempt hibernating butterflies onto the wing was 12 April when several Small Tortoiseshells and Peacocks were nectaring on the dandelion flowers. The highlight of the day was a superb male Brimstone. The two common species were joined by Green-veined White and Small White in the last week, but the most common butterfly was the Speckled Wood. Following the first on 22 April, an amazing count of 24 was made on the 26 April. This species is the success story of the butterfly world in recent years, as it has spread northwards and colonised habitats where it was previously unknown.
Water Voles became active by the middle of the month and there were several Pipistrelle and a few Noctule bats in evidence on warm evenings.