A: The short answer is “yes”, although whether the threat is sufficiently significant to lead to appreciable declines in bird populations is a matter of considerable contention. Moreover, as we shall see, all may not be as it seems in cases where the European hedgehog (Erinaceus europaeus) has been implicated in the decline of bird species.
Hedgehogs are widely known to attack and consume the chicks of birds if they encounter a nest. In captivity, hedgehogs will readily accept any flesh and in his 1964 book, Hedgehogs, Konrad Herter writes of a lactating hedgehog that ate 120 grams (4.2 oz.) of chicken, a sparrow (weighing 24 g. / 0.8 oz.) and 85 g. (3 oz.) of milk in a single night (representing a good third of her weight); another captive hedgehog seemed quite happy being fed nothing but sparrows for ten days, so it seems that birds aren’t overlooked if the opportunity arises. Indeed, in his 2007 The New Hedgehog Book, Pat Morris notes how chicks are eagerly attacked and eaten, in what he refers to as “a gruesome manner”. The idea that hedgehogs will eat chicks seems to be supported by stomach content analysis: in a study of a gull colony in Cumbria, biologist Hans Kruuk identified gull-chick down in 30% of hedgehog faeces, while a study of hedgehogs in New Zealand found avian remains (largely feathers) in 10% of guts analysed. Unfortunately, it is difficult to separate active predation from scavenging when dealing with stomach and faecal analyses.
Records of chick predation by hedgehogs may be relatively scarce in the literature, but accounts of them consuming eggs are not – there have been many attempts (some scientific, other less so) to discern the palatability of different eggs to hedgehogs and to get a handle on the level of nest predation attributable to this mammal. Before we look at the data, it is worth taking a moment to consider why hedgehogs would want to eat eggs in the first place.
The eggs of most vertebrates are telolecithal; this means that the yolk mass is separate from the developing embryo (as opposed to most invertebrates, where the yolk is incorporated into the dividing cells). As such, when you crack open, say, a chicken’s egg, you will find a yellow (depending on the bird’s diet) yolk surrounded by a ‘gloopy’ clear liquid: the ‘white’ or albumen. The egg white is cytoplasm and is effectively protein dissolved in water (the white is about 90% water); it protects the valuable yolk and provides an additional source of nutrients for the developing chick. The white protects the yolk because it is full of proteins that serve to digest bacterial walls, block digestive enzymes, repair holes in the shell, thicken the albumen (which serves to inhibit viruses) and bind various vitamins and minerals. Consequently, it perhaps comes as no surprise that most of the egg’s ‘goodness’ (here we mean calories, fats, cholesterol, folate, vitamins, calcium, iron etc.) are found in the yolk. Indeed, the yolk is the main source of nutrition for the developing embryo; it contains all the fat and cholesterol as well as all the fat-soluble vitamins and various saturated and unsaturated fatty acids. Overall, The Diet Channel sum up succinctly why any animal would want to “go to work on an egg” (an advertising slogan used by the Egg Marketing Board during the 1950s), when they describe eggs as “one of Nature’s great nutrition powerhouses.”
Eggs have long been identified from the stomach analyses of hedgehogs, although many hedgehog enthusiasts have argued that this is perhaps to be expected, given that egg is commonly the bait in traps used to catch hedgehogs. Indeed, whether or not hedgehogs are interested in, or capable to gaining entry to, birds’ eggs is a subject of much conjecture and argument. In his 1987 book, The Complete Hedgehog, Les Stocker writes that it is a physical impossibility for a hedgehog to break into a duck’s egg and unlikely that it could do much damage to an unbroken tern’s egg; its jaws are just too small and weak to be able to crack the shell. Mr. Stocker also notes how, even when given no other food for a week, a hedgehog was still uninterested in eggs. Mr. Stocker’s view is echoed by other authors. In their book, The Natural Hedgehog, Lenni Sykes and Jane Durrant mention that during their experiments on captive hogs at the Welsh Hedgehog Hospital, they found that these animals were uninterested in hen and quail eggs unless the shell was broken for them – the authors suggest that the hedgehogs were unable to open the eggs themselves and showed no interest in even trying. Similarly, in Hedgehogs, Konrad Herter notes that hedgehogs probably do eat the eggs of ground-nesting birds like quail, larks and partridges, but that larger eggs or eggs with thicker shells would be largely invulnerable to them.
Fri Jan 06, 2012 12:32 pm
