Signs of Fall 8: Interacting With Birds

Photo by D. Sillman

Photo by D. Sillman

Last winter I wrote about Helen MacDonald (the author of H is for Hawk) and her N.Y. Times article entitled “Why do we feed wild animals?” The primary motivation, according to MacDonald, that leads us each year to spend three billion dollars a year on wild bird feed alone, is to feel like we are part of the natural world! As MacDonald wrote so eloquently, feeding wild animals “surrounds us with creatures that know us, are able to forge bonds with us, have come to regard us as part of their world.”

Now there are good consequences and bad consequences when the animals have humans as their worldly companions. With expanding food sources latitudinal ranges can be expanded (as we noted for North American cardinals (Cardinalis cardinalis) and goldfinches (Spinus tristis)), migration routes (and all of the stresses and dangers associated with migration) can be shortened (as we noted for the Eurasian blackcap (Sylvia atricapilla), and spring breeding health and nestling vigor and survival can be improved (as we noted for populations of Wisconsin, black-capped chickadees (Poecile atricapillus)). We also have seen, though, that diseases can be more easily spread between birds feeding in densely utilized, human-made feeding stations (as in the case of house finches (Haemorhous mexicanus) and the epidemic spread of mycoplasmal conjunctivitis), and the reproductive successes of feeder fed vs. naturally fed birds (as in a study in England on the blue tit (Cyanistes caeruleus) and the great tit (Parus major) (two European relatives of the chickadee)) can be quite different if the provided bird seed is poor in nutritional quality (high fat, low protein with low levels of essential nutrients). Feeder fed birds in this study laid fewer eggs, had fewer fledges and had a significantly reduced overall level of reproductive success.

Photo by T. Bresson, Wikimedia Commons

Photo by T. Bresson, Wikimedia Commons

Last spring a paper was published in the journal Movement Ecology by scientists from the University of East Anglia and the University of Lisbon that looked at the influence of open landfills in Portugal on the yearly migration patterns of white storks (Ciconia ciconia). Using GPS/GSM trackers that they attached to a cohort of storks (not an easy task, I am sure!) they confirmed observations that had been made at a number of these Portuguese landfills that the storks were increasingly bypassing their long, winter migration to sub-Saharan Africa and were remaining in Portugal through the winter to gorge on garbage in the landfills. The storks were also observed to eat many forms of non-food trash including paper and computer parts and often got their long beaks entangled in the rotting debris.

It would be interesting to study the influences of this low quality and possibly toxic diet on the life expectancy and reproductive outcomes of the storks. Fortunately, though, a long-term study of this system will not be possible since the European Union has mandated the closure of the Portuguese landfills by 2018 (they will be replaced by composting factories). How the garbage adapted storks will react to the sudden loss of their food supply is another good topic for a study!

Photo by G.G. Ioham-Braun, Wikimedia Commons

Photo by G.G. Ioham-Braun, Wikimedia Commons

On a less disgusting note, a paper was published this summer in Science (July 22, 2016) in which the communication biology between humans (members of the Yao people of Mozambique) and the greater honeyguide bird (Indicator indicator) was examined. The Yao regularly search for honey in the forests around their villages and often recruit a honeyguide bird (an African cuckoo species) to assist them in finding the honey-rich bee nests. Birds that participate in successful hunts are rewarded with a piece of honeycomb (a highly desirable food item for the bird!). The Yao use particular vocalizations (especially a “brrr-hum” sound) to attract and maintain contact with their honeyguides. Scientists from the University of Cambridge and several institutions of South Africa wanted to determine if the vocalizations used by the Yao were specific to attracting the honeyguides, or if more generalized sounds directed at a passing bird would also elicit the mutualistic hunting behavior.

Using high quality recordings in the field, these scientists clearly showed that the specific “brr-hum” call was interpreted by the honeyguides as a call to join humans in a hunt for bee’s nests. The honeyguides do feed on bee’s wax on their own, but approaching a bee nest can be quite a dangerous task for them. Multiple bee stings can actually kill an adult honeyguide. So, the mobilization of humans with their technologies (axes, saws, and smoke) greatly reduces the probability of injury and greatly increases the likely of a good meal of bee’s wax at the end of the day!

Anthropologists classify this vocalization specialization between humans and honeyguides as a true and possibly quite recent co-evolutionary event. The Yao, of course, learn this relationship as a generationally conveyed component of their complex culture. It would be interesting to see if the honeyguides also learn their roles in the hunt as a cultural trait passed down from parents to offspring, or if there is a more hardwired, genetic component to their behavior.

Photo by U.S. Geological Survey, Public Domain

Photo by U.S. Geological Survey, Public Domain

And finally, a very disturbing study also published this summer in journal mBio (July 26, 2016) examined a phenomenon in Alaskan black-capped chickadees that had been observed since the 1990’s: overgrown, warped beaks that cause an affected bird to be unable to groom or eat. This condition turns out to be caused by a new picornavirus called “poecivirus” (after the black-capped chickadees’ scientific name, Poecile atricapillus). This disease is a type of “avian keratin disorder,” and it causes the top and bottom of the beak to grow out in opposite, curving directions.

The virus directly affects the fibrous protein layer around the bone and disrupts the normal growth and repair homeostasis of the beak. Avian keratin diseases (which are caused by several other types of viruses) are found in twenty-four bird species in North America and thirty-six species in the United Kingdom. It is not clear how easily transmitted this new virus is and whether it represents another potential threat to birds feeding in high densities at human stocked bird feeders.

So, to be safe let’s all try to remember to keep our bird feeders clean and well stocked with high quality seed! Also, let’s all work hard to keep our individual contributions to our local landfills as minimal as possible! We don’t want our great blue herons or any other birds to take up the garbage-feeding behaviors of the Portuguese white storks. And, finally, we may not have honeyguides in Western Pennsylvania to lead us to caches of wild honey, but we do have a wide range of more subtle mutualistic symbioses to enjoy. We just have to open our eyes to find them!

 

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