Stripe-backed bittern

The stripe-backed bittern is easily confused with the least bittern. The most striking difference consist of the contrast between the dark coloured, completely streak less back of the least bittern, compared to its patterned wings [8]. Least bitterns also differ by the rufous coloration on the sides of their head, also present on the neck of females [6].

Displaying a disjunct, yet wide distribution, stripe-backed bitterns are found on each side of the Andes. A northern population is distributed in large patches across South America, located in Colombia, Venezuela, Guyana, Suriname, French Guiana and the island of Trinidad, while a southern population is found in central and southern South America; in Paraguay, Uruguay, Argentina, Chile, southern Brazil and Bolivia [6]. In 2018, the presence of stripe-backed bitterns have also been confirmed in northeastern Ecuador, as well as in southeastern Peru [6].

Freshwater sources are favoured as habitats for stripe-backed bitterns. Ideal ecological niches consist of highly vegetated reed beds, swamps, rushes, lakes and mountain streams, marshes, and rice fields [6][7]. Such aquatic environments are essential in food acquisition, and in requirements for nest building.

The most prominent food source for stripe-backed bitterns, comprising half of their overall diet, are insects. More specifically, they preferably consume insects from the orders Odonata, Coleoptera, Hemiptera and Orthoptera [9]. The remaining half of their food intake is sourced from small fishes, crustaceans, and arachnids [9][10]. Stripe-backed bitterns are diurnal birds. They tend to intensify their activities such as active hunting either early in the morning or in the afternoon, prioritizing rest at noon and at sunset [9]. They have been recorded to feed either alone, or in pairs [10]. Night feeding has also been reported, but only scarcely.

The reproduction cycle and breeding details of stripe-backed bitterns have not been extensively studied, and much of it is still unknown. What we do know is that this species is not a strong flier, and only does fly across short distances. Their nests are consequently not found high up in trees. Stripe-backed bitterns makes small nests of tightly bound reeds and stems, which are found above water level, among reeds[7]. Incubation period for eggs is unknown, and breeding seasons appear to vary widely based on location.

Stripe-backed bitterns have not been represented widely in the literature, especially due to the rarity of sight, as well as the scarcity of information concerning many of their life history traits. However, one topic has often resurged throughout history; the evolutionary explanation for stripe-backed bitterns’ distinct egg colour.

Ardeidae is a family of birds known to yield eggs of either elliptical or spherical shape, which are often pale blue in colour [2].  The translucent layer of their eggs, combining the commonly called cone and palisade layers, allows a glimpse into the blue or white inner shell [2]. The eggs of stripe-backed bitterns, uniquely, exhibit pale blue cone and palisade layers, covered by an outer translucent green layer [2]. Although recurrent observations/descriptions have been published, the evolutionary explanation for such a unique egg coloration within the Ardeidae bird family, remains unsolved to this day.

Sounds have been elaborately described and are sometimes the best way to determine the presence of stripe-backed bitterns, emitting calls through distinct, low-pitched ooks, or through gargling [7]. Territorial or warning vocalizations consist of four low-pitched short “huu” or “ook” notes, followed by a second type of vocalization; a faster and higher-pitched “g’u’u’u’a’a” gargle [7].