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Kentucky Warbler Recapture and Cabo Blanco Birds

Posted on Jan 4, 2015

The first session of our fourth year at Cabo Blanco is in the books. Cabo Blanco is Costa Rica’s first national preserve, established over fifty years ago. The preserve is mostly one generation of forest that has re-grown over a 60-year period. It was once all primary forest, but was cut down for farmland. We start the morning walking up a winding trail to our banding station tucked away near a few fallen trees. Along trails we’ve secretly cut are twenty well-placed mist nests to catch a wide variety of avifauna that uses the preserves habitat.

Spider web
Once we reach the base camp every morning we wait, and the thing that always resonates with me to signal that it’s time to open the nets are the secrets that begin to unfold as soon as that morning sun peaks through the dense canopy. Spider webs through out the surrounding areas are hidden away until that first light reaches them and they illuminate like roadway signs. Just like our nets the spider webs are perfectly placed to catch prey. We band throughout the day till 12:00, when the topical sun starts to make the forest so hot the birds move less to conserve energy.

After three days we had a nice variety of birds and some interesting data collected. First and foremost are the migrants that we are looking to catch, as our main objective is studying their wintering habitat preferences and survival rates. One of our main targets is the Kentucky Warbler (Oporornis formosus), a medium ground-dwelling warbler found in a mix of habitat breeding in the states. They are a declining at a rate of around 1% per year, mostly due to the destruction of understory by White-tailed Deer.  This was actually the first species of bird we banded in the preserve four years ago. We have caught a steady rate of individuals over the years, and sometimes we get very lucky, like this year, and one actually returns! This year a banded female Kentucky Warbler returned to Cabo Blanco after we banded it last year.

Kentucky Warbler (Oporornis formosus)
This bird migrated all the way to Cabo Blanco, back to the states, hopefully successfully bred, then flew all the way back to the relatively small tract of land that is Cabo Blanco – possibly over a 10,000-mile journey. It’s amazing that these small birds that weigh only a few grams can take such a journey and make it back through the ocean of green forest, across Central America, and back to our net array to be captured again.

We also caught another very interesting North American migrant, the Wood Thrush (Hylocichla mustelina). What makes this catch of particular interest is the fact they’re not supposed to be migrating through the Pacific side of Costa Rica. While we have caught Wood Thrush consistently over the years at Cabo Blanco, all previous research has pointed to the fact they are supposed to be exclusively a Central Valley and Caribbean migrant.  We are still trying to put the pieces together as why they haven’t been detected with any sense of frequency on the Pacific side.

Wood Thrush (Hylocichla mustelina)
The last migrant I want to touch on is the Worm-eating Warbler (Helmitheros vermivorus). It is a medium, stocky warbler, found breeding in dry forests in North America and a species that is found nesting in both the Connecticut and New York areas. They are a wonderfully cryptic species, so much so that in the breeding season females won’t be flushed unless touched while on their nest. Their camouflage adds to their interesting look and behavior, even in the tropics. A hard to find species even on the wintering grounds it definitely goes unnoticed until one is able to be confirm their presence through netting them. We catch them very sporadically at the site.

Worm-eating Warbler (Helmitheros vermivorus)
We also catch a wide variety of interesting residents that we are looking to study in a number of different ways; ageing and sexing birds by molt, maturation of songs in certain species, and a variety of habitat use questions. I’ll get more in to detail on some of those topics in later posts. I also wanted to include some other beautiful species highlights such as the Rufous-capped Warbler (Basileuterus rufifrons), White-tipped Dove (Leptotila verreauxi), and the ever-fascinating Stub-tailed Spadebill (Platyrinchus cancrominus).

Rufous-capped Warbler (Basileuterus rufifrons)

White-tipped Dove (Leptotila verreauxi)  Stub-tailed Spadebill (Platyrinchus cancrominus)
Next up I’ll discuss our first banding session at Curu and the frenzy of birds it always has to offer.

Sean Graesser
RTPI Affiliate