Cañada de los Osos Ecological Reserve: Youth Education

Cañada de Los Osos Bird Nest Program – 2009

House Wren  Troglodytes aedon

Western Bluebird  Sialia mexicana

Black Phoebe Sayornis nigricans

Tree Swallow Tachycineta bicolor

As was true of last year, the extended drought and erratic swings in temperature during the year affected some of our birds in a negative fashion.  Others adapted well and succeeded beyond expectations.

House Wrens.  These birds are small bundles of feathered energy.  They fill their nest box with sticks and even build false nests nearby.  They scour the brush for insects to feed their young and actively defend their nests.  Aggressive competitors, it is not unusual for them to sneak into the nests of neighbors and puncture some of the eggs.  The fewer baby birds to feed, the less sharing of food resources.  2 nests, 13 eggs, 12 young fledged. 

Bluebirds, the symbol of happiness.  They’re so family oriented that the first-born young of the year may even help with the feeding of their parent’s second family.  There is a dark side though.  Although they usually get along  well with other small birds, they have been known to kill adult swallows to take over a favored nest box.  15 nests, 73 eggs, 55 young fledged.

Black Phoebes.  These flycatchers have adopted the back of the generator shed as their home and have built their mud/grass nests there every year.  The same pair nested twice this year in the same nest.  They have re-nested in other years also but always built a new nest each time before this year.  They’re getting old – or getting smart.  2 nestings, 8 eggs, 8 young fledged.

Tree swallows.  These aerial acrobats were hardest hit by the drought and periodic cold spells.  They  feed  almost exclusively on flying insects caught in flight.  When it’s cold, or when the flowers stop blooming early and the vegetation dries up, flying insects become scarce.  The adults have to fly farther and longer, they become more prone to predation and nesting success drops.  Sometimes they have to eat some eggs just to stay alive.  In good years they may nest 2 or 3 times successfully.  Swallows tend to arrive in bunches and leave in bunches.  Once the majority raised a family, the urge to move to greener pastures took over.  A few females that started second clutches found themselves alone and most of these later nests were abandoned.  The result is a high egg count, but a lower percentage of young raised. 25 nests, 122 eggs, 84 young fledged.

We didn’t attempt to find quail or turkey nests, but they had big hatches. No rain when there were young chicks, lots of small grasshoppers at the right time, added in-ground drinkers and enhanced brush piles probably all contributed to a very successful year for these ground nesters.