Musings of a roaming nature nerd

Archive for April, 2013

Nest Searching

This field season I am monitoring Least Bell’s Vireo (LBVI) territories on a section of the San Luis Rey River. Monitoring the nests is relatively easy; show up, watch for the adults birds either foraging nearby or incubating eggs, take a peek in the nest and skedaddle. It is finding the nests that presents more of a challenge!  LBVIs are not much bigger than my thumb. They are a dusky grayish, white and are in constant motion in dense vegetation. It honestly feels at times like finding a needle in a haystack. Fortunately the males instinctively feel the need to sing as close to 100% of the time as they can. Sing, sing, sing, preen, preen, sing, sing, flutter, sing, smash a caterpillar, smash, smash, eat, sing, sing, sing. He sings while he and his female build their nest together, he sings while she incubates the eggs, he even sings periodically while he incubates the eggs. Hear a bird singing that hasn’t moved in 10 minutes? Nest!

Nonetheless, nest searching still has its challenges, such as today when I donned a full body Tyvek suit to enter a shoulder high stand of poison oak just to confirm a nest location! A few days ago my boss joined me in the field, to help sort out a challenge. I’d pin-pointed a small area as a likely nesting spot for one pair of LBVIs but hadn’t yet located the actual nest yet. We hunkered down to wait near the spot I’d focused on and heard the male singing close by. Soon we spotted him pop up from a shrub and start to forage. At this same moment we saw the female enter the shrub down low. As LBVIs typically nest only 1 meter off the ground we knew we’d nailed down the likely spot. As we continued to wait and observe, the male took off and sang about 50 meters away. Within a couple minutes he arrived back and approached the nest area. We heard her give a scolding, warning call and he backed off. Suellen whispered “Oh wow! She might actually be laying an egg right now and doesn’t want him disturbing her.”

A few more minutes passed and finally she flew out of the shrub and he flew back in. Immediately he began making these super squeaky noises and singing really fast; noises they usually only make when they are excited or agitated. Suellen again whispered “What do you want to bet, he’s excited about seeing a new egg in the nest?!” He eventually calmed down and became quieter. My excitement was still building and after a few more minutes we finally approached the site. A quick scan and I spotted him tucked into a tiny nest completely camouflaged inside the vegetation. With our approach he took off and I used the opportunity to extend my mirror pole and take a quick peak inside the nest. Two perfect little eggs sat inside. One white and one pink, pink indicating being freshly laid!

I dropped a GPS point and we hurried away so he could go back to incubating. What a thrill to not only locate the first nest I’d seen with eggs this season, but to bear witness (at least auditory witness!) to an amazing moment in the life cycle of an endangered bird. If these first observations are indicative of the season ahead, its going to be a great one!

A different male LBVI tending to a nest with three eggs!