Statistics of Swallow Nest Boxes at Buttertubs West Marsh in 2025.
Number of boxes: 30
Number of boxes with eggs: 25 (83%)
Number of eggs laid: 139
Mean clutch size (range): 5.1 (2-7)
Number of eggs hatched (% eggs hatched): 124 (89%)
Number of nestlings banded (% nestlings banded): 114 (92%)
Number of females banded: 25
Number of males banded: 1
Number fledged (% nestlings fledged): 106 (85%)
% eggs to fledglings: 76%
Fledging rate (young per pair): 3.9
Summary statistics of Tree Swallow nesting productivity at Buttertubs West Marsh during 2021-2025, and 13-year average.
| Parameter | 2021 | 2022 | 2023 | 2024 | 2025 | 13-year Average |
| Number of boxes | 36 | 36 | 36 | 30 | 30 | — |
| Number of boxes with eggs (% of boxes with eggs) | 27 (75%) | 20 (56%) | 24 (67%) | 25 (83%) | 25 (83%) | 21 (68%) |
| Number of eggs laid | 194 | 131 | 138 | 154 | 139 | 129 |
| Mean clutch size (range) | 5.1 (3-7) | 5.7 (2-7) | 5.3 (3-6) | 5.5 (2-7) | 5.1 (2-7) | 5.1 |
| Number of eggs hatched (% eggs hatched) | 119 (61%) | 116 (89%) | 120 (87%) | 104 (68%) | 124 (89%) | 97 (74%) |
| Number of nestlings banded (% nestlings banded) | 88 (74%) | 115 (99%) | 97 (81%) | 82 (79%) | 114 (92%) | 81 (85%) |
| Number fledged (% nestlings fledged) | 50 (42%) | 102 (88%) | 83 (69%) | 62 (60%) | 106 (85%) | 64 (67%) |
| % eggs to fledglings | 26% | 78% | 60% | 40% | 85% | 50% |
| Fledging rate (young per pair) | 1.3 | 4.4 | 3.2 | 2.2 | 3.9 | 2.6 |
