Seed-a-palooza

Time for an update on the seed and diet study -- one in which may explain why blog posts have been so infrequent over the past year.

Recap of RRBO's research trajectory
When RRBO was founded in 1992, there was very little research being done on how birds used urban natural areas. Our first task was to establish solid baseline data on the species, relative abundance, and seasonal distribution of birds using the UM-Dearborn campus utilizing historical data, standardized regular surveys, and bird banding. This has resulted in a variety of publications, including a book, documenting the 261 species of birds found in the city of Dearborn, mostly on campus.

Once we understood that many birds used the area, our next question was: How? Were migratory birds that stopped here able to find the resources that would enable them to continue their migratory journey? Based on our banding data, we looked at 15 years of recaptures of thrushes during fall migration, and found that all three species for which we had sufficient data -- Gray-cheeked, Swainson's, and Hermit Thrushes -- did gain enough mass to make the next leg of their migratory flight. This research was published in 2009 in The Wilson Journal of Ornithology.

That led us to another question: What were these birds eating that helped them gain weight? Fortunately, there is a reliable and low-tech way to find out: identify the seeds in their poop. Over 300 samples consisting of over 1200 seeds were analyzed from Hermit and Swainson's Thrushes, and a paper summarizing the results is in progress. The majority of samples were from two non-native plant species, Amur Honeysuckle and Common Buckthorn. This was a little surprising, because these species were said to have little nutritional value to birds.

Every "answer" leads to more questions!

Current research
Our thrush work led me to begin working on the following...

Were fruits being eaten in proportion to their abundance in the landscape?
Last year I finished up censusing fruit in a large plot to provide us with a sense of the rank abundance of all the ripe fruit available to birds to eat throughout the fall season. The end of this post describes that work.

Were there some intrinsic characteristics (size, number of seeds, etc.) of the fruits that made some more apt to be consumed than others?
This fall and winter I will be finishing up the fruit morphology work, which I first described in detail in this post. I will have detailed data on many physical characteristics of the fruit of 40 species of fall-fruiting plants, based on measurements of over 6500 fruits and over 9000 seeds (so far!). I'll be preparing a paper on this data for The Michigan Botanist.

Were migratory thrushes eating non-native fruits because resident birds had already eaten the "better" native fruits before the thrushes arrived?

In 2009, we started collecting fecal samples from all bird other species we banded. Two things became immediately clear. First, other birds began eating honeysuckles and buckthorn as soon as they became ripe, even when native species like pokeweed and dogwoods were available. Second, we could collect A LOT of samples from American Robins.

Robins have been RRBO's most commonly banded species, although they are poor subjects for mass gain studies. We rarely recapture them and we cannot distinguish which nested in the area and which were migrants (thus making it impossible to estimate stopover duration and obscuring mass gain patterns).

Since we don't need to rely on mass gain data, we don't need to capture robins and can use "seed traps" to collect robin samples. Often, seed trap arrays are plastic trays with drainage and screen tops placed throughout an area frequented by birds. This is a costly method in an area like ours where field equipment is frequently vandalized. Fortunately, robins have the habit of gathering at drinking and bath sites, during which time they nearly always poop. We began collecting samples from robins when we were able to observe a flock around puddles or foraging in a specific area within our study plot. When a small retention pond was constructed right outside the banding lab, we set  out boards along the margins -- these made excellent seed traps! In 2013, we also began collecting samples at a Washtenaw County site which has more native fruiting plants and fewer non-natives (especially honeysuckle) to use as a comparison, using similar methods.

This fall, 949 samples were collected from robins, bringing the 2009-2015 fall total of samples to 2207 consisting of 16931 seeds, of which only one was unidentified! And why stop in fall? Robins are here nearly year-round, so we have continued to collect in winter, and have 350 samples (2252 seeds). At the Washtenaw County site the total number of robin samples is 1135 (6327 seeds) for fall and 792 (4515 seeds) for winter just over the past two years. Summer samples are being collected as well, although fewer plants fruit in summer. Samples are also collected from all species banded at the Washtenaw site.

So far, altogether, from both sites for all species throughout the year, RRBO has collected and compiled data on over 5300 samples consisting of over 35000 seeds.

This very robust data set will show us what fruits robins eat (and therefore disperse in the landscape) throughout the year in both an urban and more rural setting. 

Because fruit crops vary from year to year, I want to continue the collection (especially in winter) for at least another year. I'll have to draw the line at some point in order to dedicate some large blocks of time dedicated to data analysis, rather than data collection!

Introducing Craves’s Giant Barn Owl!

I recently received a great honor: a new (albeit extinct) species of owl was named after me. Craves’s Giant Barn Owl (Tyto cravesae) was recently described based on fossils discovered in Cuba by my great friend William Suárez. The bird was described in a recent paper published in the journal Zootaxa, Systematics and distribution of the giant fossil barn owls of the West Indies (Aves: Strigiformes: Tytonidae) by William, formerly a curator of the National Museum of Natural History and now living in the U.S., and Storrs L. Olson of the Smithsonian Institution.

An artist's rendering of Ornimegalonyx
at the Museo Nacional de Historia Natural
de Cuba. Even bigger than Tyto cravesae!
Photo by Darrin O'Brien.

The bones of this owl were discovered in a cave complex in Cuba by William in 1998, and subsequently in several other locations in Cuba. The paper reviews and revises previously described species, with two of those being synonymized with two others. Thus Tyto cravesae becomes the fourth extinct giant barn owl described from the West Indies.

These owls were all larger than Tyto alba, the common Barn Owl found across much of the world today, including in North America. Based on the bones found, Craves's Giant Barn Owl was likely somewhat larger than a Great Horned Owl. There were also even larger prehistoric owls in Cuba in the genus Ornimegalonyx, estimated to be a meter or more tall!

The cave deposits date from sometime in the late Pleistocene (the epoch ranging from 2.5 million to around 12,000 years ago), and include the bones of prey items.  Craves's Giant Barn Owl fed on large rodents and small mammals. The lack of other predators on mammals besides giant birds in the West Indies is the main reason these owls evolved into such large forms. "My" owl probably often preyed upon hutias, a group of rodents endemic to the Caribbean region; one species identified with the Tyto cravesae bones was that of the Cuban or Desmarest's Hutia (Capromys pilorides). The giant Antillean owls probably became extinct due to the loss of their prey species.

I got to know William during several U.S. licensed trips to Cuba in the early 2000s in which I assisted with and lead bird surveys throughout the island. William is a leading authority on Caribbean birds and mammals, both living and extinct. He has written or co-authored many papers as well as a book, and described and named several other new genera and species of birds. Over the years, we kept in continuous touch both as friends and colleagues.

In the paper describing Tyto cravesae, the section describing the naming of the species states: "After Julie Craves, of the University of Michigan-Dearborn for her dedication to avian conservation and her boundless appreciation of Cuban friends and birds." 

No matter what he has encountered, William has persevered with remarkable optimism and good humor. His strength and accomplishments have been a continual source of inspiration to me.  I am incredibly honored that he chose to name this new species of owl after me, when the true honor has been mine, simply having the opportunity to be his friend.

Julie Craves and William Suárez at the Big House, August 2014.

Read more at the BirdWatching Magazine blog, where William and I responded to questions from editor Chuck Hagner. In 2002, I also wrote an article for the magazine, The Birds of Cuba. In 2003, colleague Kim Hall and I published a paper on some of the survey's findings in the Journal of Caribbean Ornithology, Notable bird sightings from Cuba, winters 2002 and 2003 (pdf).

Yellow Rail - new Dearborn species

Another new species has been added to the Dearborn checklist. I received, through a chain of 6 people, a clear photo of a Yellow Rail at the Ford Rouge Plant from October 8. It was at a building near the Dearborn Truck Plant. There is wetland/pond habitat at the visitor center of the plant, adjacent to the truck plant that the bird may have been attracted to. I do not have permission to post the photo, but there is no doubt of the identity of the bird. 

I have no information how long/if the bird remained, but there is no public access to most of this facility. The photo showed the bird near a building. This could indicate it was injured, but I have heard of rails, including Yellow Rails, showing up in unusual locations like this during migration. Yellow Rails often try to flee by running and hiding rather than flying, yet may appear so tame as to emerge from marsh vegetation at an observer's feet. Thus, a good photo of an ambulatory rail doesn't necessarily indicate that the bird needed "rescuing."

Yellow Rails are secretive, marsh-dwelling birds that are hard to find even at known breeding locations, such as Seney National Wildlife Refuge in the Upper Peninsula. The species is listed as State Threatened in Michigan.