TROGONIDAE Trogons FAUNA PARAGUAY

TROGONIDAE - TROGONS
Three Paraguayan species in this pantropical family and, like all the New World species, belonging to the Tribe Trogonini in the subfamily Trogoninae. Johnsgard (2000) placed the three Paraguayan species in the subgenus Trogonurus or "Vermiculated Trogons" which are defined by the finely-barred wing coverts and black-tipped central retrices. The family reaches its greatest diversity in the Americas. Fossils attributed to a now extinct family Archaeotrogonidae were once though to represent ancestral forms of this family, but they are now considered to be caprimulgids. The earliest known fossil trogons that show the heterodactyl foot arrangement date from the mid-Oligocene.
Typical trogons have a short, broad-based bill with a curved culmen, giving an extremely wide gape. The base of the bill is covered by bristly, forward-facing feathers which likely help to funnel items towards the bill when taking food in flight and the cutting edges are serrated. The tail is long and graduated, consisting of 12 retrices and with the three innermost pairs longest forming a square tip when closed. The remaining three pairs become progressively shorter towards the outermost. Trogons have short, partially-feathered tarsi and the feet have a heterodactyl toe arrangement - two toes facing forward and toes 1 and 2 directed backwards. The forward-facing toes are united along half of their length. This arrangement may help them to grip vertical surfaces when nesting. The skin is extremely thin and the feathers are loosely-attached. The muscles attached with the legs are weak and, though they are capable of doing so, trogons rarely hop or walk. They are most often seen perched erect and motionless with the tail pointing downwards. They have large flight muscles, accounting for 20% of body weight, and a large heart. The palate is schizognathous and the syrinx is tracheo-bronchial. Trogon tongues are short and triangular, with two posterior processes. The naked oil gland is non-functional.
Trogons are generally found in forested areas and have short, rounded wings and a long tail which help assist with sudden directional changes. However they are not strong fliers and most flights consist of short, undulating trips from one branch to another. They have 10 strongly-decurved primaries, the outermost being the shortest and P6 and P7 the largest. The secondaries and tertials are short and there are 10 to 12 in total. Male trogons show iridescent plumage on the upperparts, the iridescence due to feather structure - the feather barbules lack hooks. Females lack iridescence. The bright red or yellow colours of the underparts are down to lipochrome carotenoid pigments present in both sexes, but rapidly fade in museum specimens. The contour feathers are tightly-packed with long, slender aftershafts. Trogons undergo a partial moult prior to breeding and a complete post-breeding moult. Primaries are moulted outwards but the tail moult is irregular.
Trogons feed predominately on insects and arthropods, but also large quantities of fruit. Prey is usually taken in flight by gleaning. Vocalisations are simple and rhythmic, usually a long series of hollow whistles. Most species also have a churring call, likely associated with alarm, and often given whilst raising and lowering the tail.
Trogons are monogamous breeders and nest in cavities in rotten tree trunks or burrowed into substrates such as arboreal termite mounds. Both sexes participate in attending the nest. The usual clutch is 2 or 3 almost spherical, pale whitish eggs which are laid directly onto the floor of the cavity - there is no nest lining. The eggshell is smooth and thin and the eggs are incubated for 17-19 days. Hatchlings are altricial and nidicolous, developing greatly lengthened pin feathers before the emergence of the juvenile plumage - the so-called "hedgehog phase". Nestlings lack down but calluses present on the tarsi are likely an adaptation to sitting on the unlined nest floor. Trogons do not practice nest sanitation and it quickly becomes littered with a foetid mix of faeces and the remains of meals.

REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Johnsgard PA 2000 - Trogons and Quetzals of the World - Smithsonian.