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Migrants in Nicaragua – Goldenwings, Merritts and Me – Part 1

Authored by John Gerwin, Treasurer, Wake Audubon
Research Curator, Ornithology, NC Museum of Natural Sciences

I have been visiting Nicaragua since 2005. It is a country with wonderful birds, coffee and lovely people. I was invited by Dave Davenport and John Connors, who had been co-leading some ecotours to Nicaragua since 2000. They had helped a group out of Durham (Sister Communities of Durham/San Ramon=SCDSR) to set up trails and cabins for a tourist operation at a restored shade-coffee farm, called Finca Esperanza Verde (FEV), near the town of San Ramon in Matagalpa province. I was asked to initiate some bird-banding and add to their bird-watching activities and I confess I was leery of going. But after just one visit, I was smitten. For the next 7 years we did 1-2 tours/year, during March, mostly with classes from North Carolina State University or Guilford College. In 2012 FEV was put up for sale. At that time, I had two new graduate students and decided to take them to another farm north of FEV to do some studies on Golden-winged and Wilson’s warblers – two species found to be fairly common in several coffee farms in northern Nicaragua. In 2013, FEV was sold to new owners but SCDRN remained active in supporting the local community and offering its own tours. Dave, John, and I have continued to bring tour groups down each year.

We have helped to train Humberto and Omar, shown below, to be nature guides & excellent birdwatchers. Donations from recent trip participants and a generous discount from Tracy at the Wild Bird Center in Chapel Hill, paid for the purchase of 2 new pairs of Nikon binoculars.

 

 

 

 

 

 

 

The Golden-winged Warbler (GWWA) is a species now quite threatened. Population numbers have declined dramatically in the past 20 years. As is often the case, we do not fully understand why – there are numerous factors involved. And like many (I suppose most) migrants, the Golden-wing spends 5-6 months in Central or South America. And so, to do effective conservation work, there is an International coalition of biologists who are working together to get, and share, as much data as we can about GWWA, across the species entire range (that is, breeding, migration, and non-breeding).

My now-former student and I returned to FEV in 2014 to continue our studies of the GWWA. We have continued tagging individual warblers with color bands/rings, radio transmitters, and in 2015, geolocators. The radio transmitters allow us to track individual birds over very short distances/areas – the radio signal transmits about 500 meters from the bird to our receiver. With this technology we can find tagged birds and observe behaviors, e.g. how they feed, where they feed, who they are with, how much space they use, and more. In 2015 we were invited to participate in a multi-country effort to put a different type of tag on individuals of this species, that would track and record their migration. These are called geolocators. The units are solar-powered and last for up to one year. The units are attached using degradable thread tied in a figure-8 harness. They take many measurements each day to record the length of daylight, the date and time of day.  These data can be used to estimate the location of the bird at the time of the recording because daylength varies by latitude and of course, changes as the seasons do. The units record the data – they do not transmit it – so the device must be recovered in order to download the data. To do that, we have to return to where we first caught the birds and try to recapture them. We have documented that 30-50% of the GWWA’s banded in one year will return to the same site the next, which makes this species a good candidate for the use of geolocator technology. The geolocator technology is not perfect. The accuracy of the point locations is good but not great (about 50 miles). But when a bird is migrating from say, Nicaragua to Pennsylvania, a 50 mile accuracy is good enough. If the solar panels can get covered by feathers, or debris; or if the bird spends a lot of time in denser vegetation, these can negatively affect the data collection.

In 2015 we deployed 5 geolocator units. In 2016, I received a small grant to return with more help, and more units. Our work at Finca Esperanza Verde is part of a multi-country effort in collaboration with scientists at Indiana University at Pennsylvania (Dr. Jeff Larkin); Cornell University (Ruth Bennett, Ph.D. candidate); the American Bird Conservancy; Audubon NC; and Jaguar Reserve & Ecolodge north of here. In addition, Jeff and Ruth are working with scientists in Panama, Costa Rica, and Honduras to deploy geolocators as well.

In February of 2016, 4 of us went to FEV where we recaptured one of the birds from 2015 and deployed 18 more units on 17 GWWA and one Brewster’s Warbler (a hybrid between GWWA and Blue-winged Warbler).  We also visited a coffee farm just north of FEV and put geolocators on 3 warblers. In November/December I sent two of my technicians back and they recovered 5 of the 18 at FEV – they did not have time to visit the other site. We received news that the unit from 2015 failed at some point in its life – the principle investigator of this project was unable to recover any data from the unit. This was disappointing news but is a typical event in the world if research – it’s always one flap forward and two flaps back.  Jeff and Ruth are receiving units from the other countries. Hopefully a good number will provide data and by this summer, we will have generated a handful of migration maps, and we’ll know where the birds from each country went to breed.

My two technicians also discovered more disappointing news. Many of the areas where we had captured the other birds that we had tagged in February, were occupied by new birds (unbanded). We don’t know if “our” tagged birds had gone to another area after being “asked” to carry this device around for a year, or if they had not yet arrived, or just what. The devices weigh 5% of the birds’ body weight – studies of birds carrying different weights have determined that 5-6% is the upper limit for an individual bird (so we don’t exceed 5%). But there could be other factors that affect a given bird, using this technique, that we don’t fully understand yet.  So to be thorough, I came down in January, along with two Wake Audubon Young Naturalists, Olivia and Vanessa Merritt, to double check the FEV site, and visit that one other site to the north.

Olivia and Vanessa are twin sisters who have worked with me for nearly 5 years, assisting with field and museum work. They are quite experienced at putting up the nets we use to capture birds, at tagging/measuring/releasing birds, and other field tasks as needed. They recently spent 10 weeks in Spain, where their grandmother lives. While there, they assisted with some migration/bird banding on Gibraltar island and during a 4-day period there were so many birds around that each of them removed ~250 birds from the nets – that’s a lot of birds in 4 days. So down we came, on January 3^rd, to re-visit areas and assess the situation where the warblers hold territories. Another aspect of our study is to see if birds remain on territory during this non-breeding season. From similar work with Wood Thrush, we are finding that individuals seem to roam during the non-breeding season. And many do not return to the site where they were banded. I have banded many Wood Thrushes here at FEV but over the years, have not recaptured any. But in years past, a handful of our banded GWWA have returned and remained at least into March, so we’re trying to piece together this element of the species life history.

 

 

 

 

 

 

 

 

My first two field techs banded ~20 male and 3 female GWWA’s in Nov/Dec, but reported that there are still unbanded Golden-wings on the property. So we will now try to capture/band as many of those as we can. Another element of our research is to band and monitor these birds for as many years as we can, to learn what we can about which ones return, and for how many years (some migrants we’ve banded in NC returned up to 10 years). So far this trip (in two weeks) we have not found any more of the birds from last year. We will continue to tag with bands (rings, really) any new birds we can capture.

Vanessa and Olivia will also do some GPS (Global Positioning System) work to help create detailed digitized maps of the property (to outline the coffee plots, the forested plots, and other features on the landscape). We are also creating some educational documents that highlight the birds that visit the banana and hummingbird feeders. This farm has some nice cabins that can house up to 28 visitors and there are many tourists that visit between December and April of each year. So we are creating some educational material about both the resident and migratory birds that visit the feeders and are easily observed by the tourists.

Coffee is an important product for many people – those who grow it, those who export it, those who roast it, and those of us who drink it. Small “traditional” farms grow their coffee plants in the shade of taller native trees and those trees provide habitat for many birds. Thus, there are two strong connections between a place like northern Nicaragua and North Carolina: the coffee we crave, and the migratory birds we love. And now we have a third connection: a number of these coffee farms provide lodging and guides who are here to showcase the plants and animals, and the coffee process, to anyone who wishes to visit. Birdwatchers/nature lovers are a welcome addition to the economy of this region.

In subsequent posts, I will share a few adventures and discoveries during our time here. I will post images of some bird species that are local residents and which ar very much like some of our own residents, along with some familiar migrants. I will also describe the coffee-picking effort of Olivia and Vanessa and explain why they earned a whopping $0.25 (each) for their one hour of labor. So, make like our favorite local animal here, the sloth, and hang around.

 

Photos by John Gerwin except first photo by Dave Davenport.