Birds play significant roles in ecosystems throughout the world. Although they represent a diverse group of organisms that interact with their environment in multiple ways, I have not yet talked about them. I wanted to learn more about how the forest floor interacts with the avian realm, and through that initial inquiry, I luckily stumbled across this 2017 publication. Here, Zaid Al Rubaiee and his team of scientists studied how fungi influence predator-prey interactions in birds. In this blog post I will share their results and discuss the ecological intricacies these researchers present to the field of ecology.
Fungi can be found everywhere, including the skin and feathers of birds. Some fungi that live on these living surface are harmless, while others can actually reduce bird fitness. Keratinophilic fungi enzymatically break down and consume the protein kertatin, which is the main molecular constituent within feathers. Other parasitic fungi may infect the skin of birds that can reduce the production of new feathers, or lessen feather quality. With these parasitic fungal-bird interactions in mind, these researchers hypothesized that birds with a higher abundance and/or diversity of skin and feather inhabiting fungi may be easier prey. In short, compromised feather surfaces should reduce the ability of predator evasion.
Keratinophilic fungal hyphae and spores growing on keratin rich feather barbules. From Lingham-Soliar et al. 2009.
The dermal and feather fungal composition was quantified in several individuals of wood pigeon (Columba palumbus), Eurasian jay (Garrulus glandarius) and blackbird (Turdus merula). These species were targeted because they are the preferred prey of the northern goshawk (Accipiter gentilis), the widespread predator chosen for this study. There are distinct sex roles seen in Accipiter gentilis, with the larger females allocating most of her time and effort to her offspring while male goshawks do most of the hunting. Males present the dispatched prey to its partner at the nest, and the female removes feathers and sheers off pieces of meat to feed to the chicks. With the basic ecology of this species understood, 50 nests were located, and subset of the plucked feathers found beneath each nest were collected for fungal analysis. Feathers from living individuals were also collected to compare the differences from birds that failed to evade predation, vs. birds that may have (prey vs. non-prey). All in all, the feathers from 47 woodpigeons, 20 jays, and 20 blackbirds were analyzed.
The most preyed on species in this study, the common wood pigeon, Columba palumbus.
In total, 27 different fungal species were isolated from the 87 bird individuals. By comparing the fungal composition in feathers from prey vs. non-prey feathers, a significant trend was beckoning. The feathers from birds that failed to evade predation had 50% more fungal colonies growing on them. These fungi quite clearly reduced bird fitness, and may act as main drivers within avian predator-prey interactions.
Birds killed by Accipiter gentilis had significantly more fungal colonies growing on their feathers. Note the logarithmic scale. Rubaiee et al. 2017.
In a 1999, research carried out by Edward Burtt & Jann Ichida showed that the feeding ecology of different bird species had a significant influence on the composition of bacteria living on their plumage. Nearly 11% of ground foraging birds had infestations of feather degrading bacteria, while foliage-gleaning (4.7%) and aerial foragers (2.4%) had markedly lower infestation rates of destructive bacteria. This paired with the findings of Rubaiee et al. 2017 paint a fascinating ecological picture of how birds interact with the forest floor. Although resources found on the forest floor may be abundant, accessing this pool may come with a serious cost; the accumulation of feather degrading bacteria and fungi. Since birds with compromised feathers are an easier target, selection has most likely shifted the feeding ecology of bird species to access resources with a lessened parasitic threat. Feather degrading organisms like keratinophilic fungi enhance the fitness of the northern goshawk, while negatively impacting populations of the three-prey species it feeds on.