Each year, the American Birding Association (ABA) selects a particular species as its Bird of the Year. The species is selected based on a combination of character of the bird itself, how it related to birders, and how it can serve as a symbol for the birding community. This year, the ABA Bird of the Year is the Evening Grosbeaks, and as I have been studying Evening Grosbeaks for the past three years, I was especially excited by this choice. I figured the added attention on this species might lead people be curious to know about them and their biology, and so here is a bit of information on them.
Evening Grosbeaks are a fascinating species for many reasons. One of these reasons, and the one that first caught my attention, is that there have been so few studies done. For being so common a visitor to backyard bird feeders, especially in winter, I was amazed at how little was known about these beautiful birds. Do Evening Grosbeaks have a song? What do the courtship rituals involve? How many subspecies exist? Where do birds go to throughout the year? How do birds find food sources? All of these are big unknowns for the Evening Grosbeak, and that intrigues me.
But before we get into more of the unknown, here is some of what is known about this bird. It belongs to a group called the Cardueline Finches. This group includes such species as House, Cassin’s and Purple Finches; Pine Grosbeak; the Goldfinches; the Crossbills; the Redpolls; and all the Siskins. This group is found across North and South America and Eurasia. Many of these species do not have regular migratory routes, but are referred to instead as nomads. Unlike many birds, which have breeding grounds where they can be found in summer and non-breeding grounds where they can be found in winter, nomadic species move across the landscape to follow food resources wherever they happen to be. This means that where groups of birds are to be found at any given time of year can be very unpredictable. They seem to congregate where there are large concentrations of food, although how they find their food is a mystery. For the Evening Grosbeak, these food resources are usually large insect outbreaks or areas where the coniferous trees have big crop of cones. Other foods that Evening Grosbeaks seem to like are the Safflower and Black Oil Sunflower seeds they find at bird feeders. One interesting dietary foible is that they seem to have a strong affinity for salt. They have commonly been reported coming down to drink from mineral springs, and also have been shown to prefer soils that have had salt added over soils that have had nothing added.
Geographically, the Evening Grosbeak has been expanding its range into the eastern United States in the past hundred years or so. The first recorded sighting of an Evening Grosbeak in New England came in the 1890s, and the first breeding record was in 1940. One thought as to why this eastward has been taking place is the extinction of the Carolina Parakeet. When the Carolina Parakeet, North America’s only native parrot, was alive their diet consisted predominantly of large seeds. When they were driven to extinction, this food resource was left open, and the Evening Grosbeak had the equipment to break into such seeds as Bald Cypress cones which other birds were too small to tackle.
The number of subspecies of Evening Grosbeak has been a developing story since the late 1800s and has had its’ fair share of confusion. In 1874 a natural historian, Ridgeway, found that birds in Mexico looked different from the birds he was used to seeing in the eastern United States. The yellow eye-stripe of the male Mexican birds was longer and wider than eastern birds and the bills were longer, wider, and less curved. This led him to separate birds in the western half of the continent from the birds in the eastern half of the continent thereby creating two subspecies. In 1917, Joseph Grinnell at the Museum of Vertebrate Zoology at the University of California, Berkeley, took a closer look. He noticed that the birds that Ridgeway had found were representative of the birds in Mexico, but that they were subtly different from birds found in other parts of the western US. Grinnell agreed that the eastern birds represented one subspecies, but he separated the birds in the western US into four subspecies based on differences in plumage color and brightness, and slight differences in bill shape and size. The resulting five subspecies were the accepted taxonomy until 1957 when the American Ornithologists Union decided that the slight differences in bill shape and size that Grinnell had described were not enough to warrant subspecies status for some of these populations. Instead, they settled on three subspecies. The eastern birds represented one subspecies, as everyone agreed, the birds from Mexico represented a second, and birds from the rest of the western United States represented a third. Since 1957, these subspecies have been the three to have accepted taxonomic status.
Regardless of how many subspecies exist, some people have taken notice of trends that stretch across the whole species. One disturbing trend was found by scientists at the Cornell Lab of Ornithology who examined Christmas bird count and breeding bird survey data and found that numbers of Evening Grosbeaks have been declining across the country. Over the past two decades, Evening Grosbeaks have been seen at fewer and fewer sites. Additionally, the sites that still have their Evening Grosbeaks have been observing smaller and smaller flocks. Since these birds are so unpredictable in their movements, and they frequently live in the back country where Christmas bird counts are rare, it is possible that the birds are simply going to places where they are not being seen. However, since the Cornell scientists only found declines all across the country, and found no population increases even at small local locations, the continent wide population decline seems like a real possibility.
In terms of vocalizations, Evening Grosbeaks present other interesting traits. Evening Grosbeaks have a number of vocalizations. One kind of vocalization is the flight call. This is a short, single-note call that seems to function in flock movement coordination. This call has been observed to vary from population to population in different parts of the country, and the different variations seem to be quite distinct. Each variation was called a Type and given a different number. So, now different birds have been identified as producing Type 1 flight calls or Type 2 flight calls all the way up to Type 5. No bird has ever been found to make more than one Type of flight call, but birds that produce different flight call types do sometimes occur in the same place at the same time. Interestingly, when the distributions of these different flight call Types are mapped across the continent, they match where Joseph Grinnell mapped out his five subspecies!
So what is going on here? Can birds use flight calls to identify other individuals such as their mate? Do they prefer to associate with other birds that make the same type of flight call? Do the different flight call types play a role in choosing a mate? Do birds that make different flight call types prefer different sized seeds? Are the birds that make different flight call types genetically different as well? How are the differences in flight call types able to persist when these birds move around and overlap with each other? These, and other questions, are what I hope to find out. So do you have Evening Grosbeaks, the ABA Bird of the Year, coming to your feeders? Let me know, and I will report back on what I find!
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