Field Work
In 2004 under the disturbance permit provided by English Nature, the area below nest sites was searched for prey remains and splash. Most remains were found from 14th August-31st August with a few up to 11th September. A total of 37 remains were found as itemised below:
|
Area |
date |
number frogs |
number chewed 'was' pellets |
|
|
|
|
|
|
South Tyne |
14 August 2004 |
4 |
3 |
|
|
16 August 2004 |
1 |
1 |
|
|
28 August 2004 |
0 |
2 |
|
Hexhamshire |
24 August 2004 |
0 |
20 |
|
|
11 September 2004 |
0 |
1 |
|
Allen |
31 August 2004 |
0 |
3 |
|
Tyne Valley |
3rd September 2004 |
0 |
1 |
|
|
4th September 2004 |
0 |
1 |
|
|
|
|
|
|
4 areas, 5 sites |
|
5 |
32 |
Frogs
Depredated Frog remains were found at one site in the South Tyne in mid-August. Two photographs are given for 14th August 2004: 1 2 . These remains could be confused with a fungus such as Exidia glandulosa Black Witch's Butter. There seems to be some differences of opinions by raptor workers as to what frog remains look like: skeletal remains or lumps of jelly have both been mentioned by different people.
Chewed Wax Pellets
Chewed 'wax' pellets were found at single sites in the South Tyne, Allen and Hexhamshire and two sites in the Tyne Valley from mid-August to mid-September. Some photographs are given below for:
Hexhamshire 24 Aug 2004 3 4 5 6
Tyne Valley 3 Sept 2004 12
Tyne Valley 4 Sept 2004 13
Hexhamshire 11 Sept 2004 (washed out remains) 14
Some elementary tests have been made on these deposits. In particular one of the samples from Hexhamshire 24 August 2004 was defrosted in August 2005 and placed in hot water. The result was a creamy-brown liquid with no signs of wax on the surface, even after it was allowed to cool. The remains did not dissolve and close examination showed a mixture of tiny granules (grains) and fibres. The water was allowed to evaporate. The result was a substantial deposit of a very durable and hard pale brown substance. This substance is very stable, still being in its original dried form over a month later (end September 2005) after being placed on a well-lit windowsill. This substance appears to be like chitin, which is the hard component of insect shells. The fibres in the liquid might also be cellulose as found in wasp nests.
The substantial durable residue eliminates slime moulds as the source of the material. In their article Ben Waggoner and BR Speer note that: “Slime molds have almost no fossil record, which is not surprising. Not only do slime molds produce few resistant structures (except for spores, which are often overlooked or unidentifiable), but they live in moist terrestrial habitats, such as on decaying wood or fresh cow dung, where their potential for preservation is low. A few fossil slime molds have been found in amber”. The author's experience with slime moulds is that on drying out, they decompose into a fine lightweight black dust. In any event it seems strange that slime moulds should concentrate around Honey Buzzard nest sites. Large areas were searched in the woods in which the nests were found but the items above were concentrated near the nest.
Diet
It is not possible to relate closely the remains found with the actual diet of the birds. Clearly though in 2004 hymenoptera nests were a significant component in the diet from mid-August to early September at all sites and frogs appear to have been significant in the diet in the South Tyne at one site in mid-August.
Literature
The presence of chewed wax comb beneath Honey Buzzard nests is well-established in the literature. Witherby et a; (1939) mention, citing G. Niethammer [Niethammer, G, Handbuch der Deutschen Vogelkunde, Leipzig 2 (1938), not yet consulted] that pellet formation is feeble and irregular, comprising remains of wasps’ nests and chitinous debris [exoskeletons of insects]. Cramp (1980, p. 17) says of earlier work by Niethammer in 1938 and Dementriev & Gladkov in 1951 that some pellet-formation occurs but regularity and amount varies with diet. Quoting CR Tubbs, Cramp continues with “Large quantities of wasp comb from which larvae removed, found on and, late in the fledging period, beneath nests: cell walls almost always 'chewed' down and presume this material provides roughage that might not otherwise be available from high protein wasp larva diet”. An Israeli web site at http://my.ort.org.il/holon/birds/q1.html has a page for Western Honey-buzzard Pernis apivorus which says this raptor: “Will remove wasps' nests from trees and dig out ground nests with claws, chunks of chewed wax comb frequently found near nests”. Van de Mortel in European Honey-buzzard Pernis apivorus produces 3 eggs. De Takkeling 11(3): 207-208 (2003) indicates that depredated frogs were found on/underneath a nest in a poor wasp year in 2003. Roberts et al (1999) studied material brought into nests rather than collected on the ground. They recorded a number of frogs as prey.
Discussion
The chewed wax comb mentioned in the literature may well often be a misnomer in that wasps, the main hymenoptera prey, do not incorporate wax in their nests. Liquid chitinous/cellulose pellets may be a better description. If bumble bees are a significant food item, then there may of course be some wax in the pellets. The description by Niethammer above appears to be the most relevant to the pellets found in this study.
© Copyright Nick Rossiter 2005
