How do exotic food species stack up.
Fast food, is it good for bittern?
Bittern are a native, self-introduced wetland bird. According to Te Papa, fossil records indicate that the birds naturally colonised New Zealand from Australia around 1000 AD so they spent a long time living on tūna (eels) and native fish before the arrival of exotic fish species.
Bittern were reported to be seen in flocks of 50-100 birds up until the 1930’s with the last reference being a well-documented event in 1937 when a resident flushed a flock of 44 Australasian bitterns (matuku-hūrepo) from a single patch of raupō at Lake Rotorua.
Roll forward to the 20th century and now more than 90% of their wetland homes have been drained and what remains are often too degraded to provide the food and security they need leaving bittern on a slippery slope to extinction.
Bittern are starving and we think their desperation for food is driving them to take more risks ie.
- feed more in open paddocks where they don’t have cover from aerial predators – which is ok if you’re an adult bittern and can fend off harrier hawks- but not if you’re a fledgling.
- feed on lizards warming themselves up on the road exposing themselves to getting hit by vehicles
- feed in ditches beside the road exposing them even more to collisions with vehicles
..and lack of food means that they are less able to defend themselves.
You can check out our previous posts or the Habitat for Hūrepo series for checks you can make.
Apart from the obvious risks to access what seem like easy food options – we are unsure how some of the more available exotic prey species stack up nutrient wise. For instance, does the effort that it takes for a bittern to catch 100s of mosquito fish (gambusia sp) compared with one little eel provide the same gains?
Hopping good food?
Mitch de Beer documented a bittern eating 4 separate eel and a frog (in the feature image here) in a series of now infamous images shared on facebook. Frogs seem to be an important target species for bittern and often when bittern are detected in sound files, we also hear frogs.
The green and golden bell frog which rapidly dispersed after being deliberately introduced to control insects in the 1860s in the North island and parts of the South Island, and the Southern Brown Tree Frog (whistling frog) which arrived soon after dispersing through the South, Stewart and lower North Island may have been a valuable source of food for bittern.
Though New Zealand was originally a safe refuge for the species with numbers growing to abundance the lethal chytrid fungus (Batrachochytrium dendrobatidis) caused a major population decline around 1999/2000.
So should frogs be back on the menu?
LOVE BITTERN PROJECT 