The type of food a heron chooses depends on the time of year and what is locally abundant in that season. Pellets collected from breeding colonies provide clues to which prey the adults are catching. Heron chicks are reliant on their parents for a long time, spending about 50 days in the nest, and they may not be independent until they are 80 days old. Herons are very adaptable hunters and can react to changes in prey availability, so the food brought to the chicks may change over the weeks. When there are plenty of small ducklings in May and early June, these can make up a large part of their diet. Some colonies feed mostly on small mammals such as water voles, mice, rats and even young rabbits. Although they are usually seen hunting in or near ponds and rivers, during the winter herons may hunt away from water, looking for small mammals in fields and pastures.
Herons will also make the most of a well-stocked garden pond if they find one, so if you want to hang on to your fish, try covering the pond with a fine mesh net and provide hiding places for the fish by planting waterlilies and other aquatic plants. You can also make it more difficult for herons to get to the water’s edge by encircling the pond with a barrier of taut strings or wires 20 centimetres and 35 centimetres above the water level. Herons are pretty bright birds so plastic decoy herons don’t appear to be much of a deterrent and may even attract a heron to hunt.
Purrfect
Do wildcats sound the same as domestic cats? Do they purr? Avril
As most cat owners know, domestic cats communicate with a variety of calls and vocalisations including hisses, growls, chatters, as well as the more familiar purring and meowing. Hissing and growling are clear signs that a cat is feeling threatened or angry. A female will ‘caterwaul’ when she is fertile – a bloodcurdling wail that advertises to local males that she is ready to mate. Kittens meow to their mothers to request food or attention and an adult pet cat continues this behaviour with its human owner. Those plaintive cries asking to be fed, let inside from the rain or demanding to be stroked are hard to ignore! Whatever delusions of grandeur your moggy may have, only a few large cats such as lions, tigers and leopards can roar.
It’s very difficult to determine exactly when cats became domesticated because the skeletons of domestic cats and their wild predecessors are so similar. However, the skeleton of a domestic cat was found with its owner at an archeological site in Cyprus, having been buried about 9,500 years ago, so domestication must have occurred before then. Genetic studies suggest that cats began living with humans when agriculture blossomed in the Fertile Crescent of the Middle East around 12,000 years ago. Wildcats were probably attracted by the rodent pests that were drawn to our ancestors’ grain stores and stayed to take advantage of this food source. No doubt, humans would have welcomed these cats if they helped to keep pests at bay. The origins of our pet cats are a bit murky but biologists suspect that their ancestors include the African and European wildcats, both subspecies of Felis sylvestris that might have interbred in the Middle East region.
Wildcats are found across Europe but in the UK they are restricted to Scotland where they are considered to be a unique subspecies, Felis silvestris grampia. They are superficially quite similar to our domestic cats and can interbreed with them, but their behaviour is quite different to that of a pet tabby that will sit on your knee. They are truly wild creatures and very elusive in their natural habitat.
Scottish wildcats lead a solitary life most of the time so, although they can make the same vocalisations as domestic cats, they generally remain silent. Instead they communicate by scent, marking their territories with faeces, urine or their scent glands. They only become vocal when they meet another cat during the breeding season or when they have kittens.
Most species of cat, large and small, can purr. Exactly how cats produce the purring sound is not yet understood entirely, but it is thought that the glottis (the area of the larynx with the vocal cords) is rapidly expanded and contracted as the cat breathes in and out, creating the characteristic vibration sounds. (We contract our glottis to create an ‘h’ sound in speech.) Unlike domestic cats, adult wildcats do not purr. Kittens purr from birth, especially when they are suckling, and purring is often interpreted to mean that the cat is content or happy. However, adult domestic cats sometimes purr during stressful situations or when they are in pain, perhaps as a means to comfort themselves or encourage others to provide care. Cats have learned that purring is a virtuous cycle – by showing pleasure they receive more pleasure, whether they are manipulating their mother or a cat-loving human.
Eggstatic
How can a tiny bird lay three or four eggs that have a total volume similar to that of themselves? Lin
Which bird lays the most eggs in one go? Dicky
Producing eggs requires a lot of effort and energy. In robins, for example, a complete clutch may be equivalent to 90 per cent of the female’s body weight. During the laying period, female birds need to rest and eat extra calories – they often rely on their partner to bring them food. Each egg must be provided with a fat-rich yolk to feed the growing embryo, which is surrounded by egg white (albumen) and then encased in a calcium-rich shell. Not only is finding extra food and producing the eggs energetically costly but birds also have to raise their metabolic rate to generate enough warmth to incubate them.
Most songbirds lay just one egg per day while larger species such as swans or geese may have a one- or two-day interval between eggs. Eggs are heavy, and if the female retained them inside her body they would weigh her down, so as soon as an egg has formed it is laid. In the UK, the grey partridge has the largest clutch of any bird, usually 14–15 eggs in total, but they can lay up to 20 eggs. Clutches tend to be larger in species with chicks that can feed themselves soon after hatching, such as many waterfowl, while species whose chicks need more care and attention have smaller clutches. Many seabirds are long-lived and have just one egg per season, investing a lot of time and energy into feeding and raising a single chick.
Some birds, like great tits, have a single large clutch per year to coincide with a peak in food (caterpillars in the great tit’s case), literally putting all their eggs in one basket. If the parents get the timing wrong or if their food supply fails they will have little breeding success. Other species, such as robins, spread their risk and can squeeze in two, three or even more clutches, especially if one brood fails, but have fewer eggs in each clutch.
The embryos inside fertilised eggs don’t begin to develop until they are incubated by the parent. Some species, such as barn owls, start incubation as soon as the first egg is laid so the eggs hatch asynchronously over several days. This means that the first chicks are much larger than later ones and may even eat their younger siblings if food is scarce, as we saw on Springwatch with a barn owl chick named Hannibal. Most songbirds delay incubation until the clutch is complete, in which case all the eggs hatch at roughly the same time and the chicks are all a similar size. There may still be a runt of the clutch, because the final egg sometimes has fewer resources put into it, but generally each of these chicks has a more even chance of survival.
Make Mine a Double
I ate a double-yolk egg for my lunch. If it had been fertilised, would two chicks have grown/hatched from one egg? Charlotte
Double-yolk eggs are fairly rare – it’s thought that about one in a thousand commercial hens’ eggs have two yolks, and multiple yolks (triple, quadruple or more) are even rarer.
They are a result of a malfunction in the chicken’s