BIO 203


Non-nesting females trick others into raising their young by laying eggs in their nests!    The bar-headed goose’s diet changes seasonally. It is consistently a primary —herbivorous—consumer, although it will occasionally feed on small insects and snails. From January through February, it primarily feeds on grasses until seeds become a staple of its diet in March. Then it feeds on field crops, such as wheat, as they become in season (Middleton and Van Der Valk, 1987). The bar-headed goose also often feeds on rice (Tampa's Lowry Park Zoo, 2014). Crop foraging is only a minor interaction with humans compared to the goose’s ability to spread bird flu viruses.
    The bar-headed goose has been the subject of major studies as to how its migration pattern influences the outbreak of the bird flu, such as H5N1. As a host to this virus, there is a high correlation between outbreak origin and one of the largest of the bird’s nesting sites, Qinghai Lake, in China. In Mongolia, outbreak of this influenza occurred within months of migration through the country. Similarly, the bar-headed goose’s entire route, spanning from Myanmar through China to Mongolia, exhibits the devastating repercussions of the bird’s role in influenza virus spread and outbreak (Prosser et al., 2009). The extent of wild birds’ role in spreading H5N1 is not fully known; evidence from studies tracking the bar-headed goose and the ruddy shelduck (Tadorna Ferruginea) provided strong evidence toward their role as major carriers (Prosser et al., 2009).
    One of the most unique of the bar-headed goose’s interactions takes place within its own species. In the first two years of age, many female geese will become “parasites” to nesting females by laying their eggs in various nests when they lack a nest of their own (Weighmann and Lamprecht, 1991). This behavior ultimately decreases the investment nesting females can give to their own offspring as well as the parasite’s. According to a study performed with semi-captive geese, only about 5-6% of parasitic eggs hatch successfully, and the number of non-parasitic eggs to hatch successfully decreased from 67% to 29% in parasitized nests. Nonetheless, the intriguing existence of intraspecies “parasites” could be highly adaptive, as more birds can reproduce without having access to nests during difficult conditions, increasing genetic variation. Then, in good conditions, all birds are capable of nesting and reproducing very effectively (Weighmann and Lamprecht, 1991). Interestingly, the bar-headed goose isn't the only bird with this behavioral adaptation. Another bird that exhibits similar nest parasitism is the tree swallow (Whittingham and Dunn, 2001).


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