#temperate forests

Horsing Around with Horse Flies

Though horse flies are regarded worldwide as pests, members of the family Tabanidae are an important part of their natural environments. Adults feed on nectar, and some are specialized pollinators that have evolved to only collect from a few select flowers. Just like mosquitoes, only female horse flies feed on blood. Reproduction requires moisture; typically clean, stagnant or slow-moving water. Because of this, some species of horse fly are excellent indicators of an ecosystem’s health. Their role as disease carriers is also a valuable part of any functioning ecosystem; diseases can keep animal populations in check, and sick animals are often easier targets for predators. Horse flies themselves are also a juicy treat for amphibians, reptiles, and birds, as well as insects like wasps and spiders.

There are about 4,455 species of Tabanidae flies, the majority of which reside in the genus Tabanus. Most species share the same general body shape: a large head, a fat body supported by six legs, and one pair of wings. However, there are many variations on this pattern in terms of size, color, and specialized appendages. The smallest horse flies are only 5 mm (0.19 in) long, while the largest is over 30 mm (1.18 in). Like other flies, horse flies have a set of compound eyes made up of thousands of ommatidia: specialised units which allow them to combine input from multiple angles. The resulting image has a poor resolution, but it’s useful for detecting rapid movement-- an important tool when trying to avoid predators. The eyes of male horse flies are holoptic, meaning they meet in the middle to give the appearence of one continuous eye.

Horse flies go through a complete metamorphosis, also known as holometabolism, over the course of their lives. Eggs are laid of clusters of anywhere from 100 to 1000, typically on plants near a source of fresh water. After about six days, the larvae hatch and drop down into the water or burrow into the moist ground, and use a respiratory siphon to pull air from the surface. In temperate regions the grubs enter a stage of dormancy, while tropical horse flies develop year-round. While in this stage individuals consume a number of other insect larvae, worms, and aquatic insects. Once fully developed the horse fly larva pupates for one to three weeks, after which it emerges as a fully-grown adult. Mating can occur as soon as the wings have fully expanded, although female horse flies need to feed on large quantities of blood before depositing the egg mass, in order to provide her young with the nutrients they need to develop.

Conservation status: No horse fly species has been evaluated by the IUCN, and due to their large numbers  populations are considered stable. However, some species only live in certain habitats, particularly wetlands, which are threatened by pollution or destruction.

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Photos

Large marsh horse fly (Tabanus autumnalis) by AJ Cann

Greenhead horse fly (Tabanus nigrovittatus) by Claudia Husseneder

The Wonderful Acorn Woodpecker

Although woodpeckers are generally solitary creatures, acorn woodpeckers (Melanerpes formicivorus) are the exception. They have intense social lives, living in large broods centered around a granary tree; a large, usually older tree in which they store their acorns. Not only do they live together they work together. Acorn woodpeckers are cooperative breeders; a rare trait in birds. This means that the group raises all their young together, and adult offspring help take care of their younger siblings. Only 9% of bird species raise their young this way. 

    The granary trees acorn woodpeckers reside in are also unique. Rather than drilling one large hollow, characteristic of other woodpecker species, acorn woodpeckers drill a series of smaller, shallower holes along the trunk. Each hole is filled with a single acorn. Established granary trees can hold thousands of acorns in this manner. In addition to acorns, M. formicivorus also feeds on tree sap, fruit, oak catkins, and insects. However, acorns are their primary food and critical for survival through the winter. Most of their time, when not feeding, is spent caring for young, maintaining the granary tree and defending it from potential thieves, such as Stellar’s jays, western scrub jays, squirrels, or acorn woodpeckers from rival units. 

    Because of their large group dynamic, acorn woodpecker breeding systems range from monogamy to cooperative polygyny. Groups generally consist of 1-7 breeding males and 1-3 breeding females. There appears to be no courtship displays prior to mating, and female choice is fickle and random. However, inbreeding has been only rarely observed. The females all nest together, laying up to five eggs each in the same hollow. Occasionally nesting females will destroy the eggs of their competitors, but once cooperative egg-laying begins, all destruction stops. Both males and females will incubate the eggs for eleven days, at which point the chicks hatch. The young are then reared by all members of the group, both breeding and non-breeding, until they reach maturtity at about 30 days old. 

    Size-wise, acorn woodpeckers are fairly average birds. They’re typically about eight inches long and weigh a little over three ounces. Their markings make them easy to distinguish from other birds and other woodpecker species; their bodies are black, with a white band around the beak and throat. Additionally, both males and females sport a red crest, although the female crest is slightly smaller and duller. Lastly, they have distinctive white wing patches that are most visible during their acrobatic flight patterns. When hidden, they can be identified by their unmistakable “rusty hinge”-like call. Acorn woodpeckers typically prefer pine-oak woodlands, and oaks are their preferred tree for their granaries. They can also be found in urban parks, oak savannas, and semi-tropical forests along the Pacific coast, ranging from the northwest United States to southern Central America. 

The Return of the #Forest: how #trees reconquered the #European #continent after the last #Ice #Age

Marco Mina About 5,000 years ago, European trees reached their widest extension towards north, and the alpine tree lines started to look like the one we see today.

People who are interested in the ecology of European forests know that the current climatic gradient has a big influence in shaping the distribution and diversity of tree species in the continent. Shrubs and evergreen broadleaves in…