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Flammulated Owl Research

The Avian Center conducted a long-term study of Flammulated Owls on Oso Ridge in New Mexico from 1996 to 2006.  Owls nested in 47 different natural nest cavities on the study site, almost half of which have been used more than one year.  We experimentally put up ten nest boxes in 2004 where Flammulated Owls were known to occur, but few natural cavities existed.  Three of those nest boxes were used by Flammulated Owls, and two by Western Bluebirds.  With such great success, we constructed more boxes and put them up in fall 2004 and spring 2006 and there are now a total of 52 nest boxes on the study site.  Click here for an abstract of 2007 results.

In the natural part of our study area, 17% of the nesting cavities have been lost since 1996, most from old age and natural causes, such as this wind-blown oak.  Two nesting trees were cut down by firewood cutters.

We made three box sizes with two different entrance hole sizes for a total of 4 box types: 1. 10 in. wide x 20 in. high with 3 in. entrance; 2. 8 in. wide x 14 in. high with 3 in. entrance; 3. 8 in. wide x 14 in. high with 2 in. entrance; 4. 8 in. wide x 8 in. high with 2 in. entrance.  We put at least two inches of wood shavings at the bottom of each box.

The map below shows the distribution of 47 owl nests (blue dots) and 52 nest boxes (green dots).  Almost 45% of the natural cavities were used for more than one year.  The east half of the map below is the natural part of the study area where nest boxes will not be erected.  Seventeen percent of the natural nest cavities in the study area have already been lost since 1996.  There have been a few nests in natural cavities on the west side of the study area, but despite the forest being relatively similar in much of the area, natural cavities are lacking.  Thus, we put up 52 nest boxes, placed randomly throughout a designated nest box area (i.e. the west side of the study area).

The following are abstracts of results published from this study.  Click on the title for a pdf file of the paper.

Mark-recapture and DNA fingerprinting data reveal high breeding site fidelity, low natal philopatry, and low levels of genetic population differentiation in Flammulated Owls

We used mark-recapture in a population of Flammulated Owls in the Zuni Mountains, New Mexico to estimate adult breeding site fidelity, natal philopatry, and dispersal in this species.  We also used DNA fingerprinting to examine the genetic population structure of Flammulated Owls in four mountain ranges in New Mexico, and one range in Utah.  Mark-recapture revealed that adults were site faithful and maintained between-year pair bonds, whereas juveniles showed little natal philopatry.  DNA fingerprinting revealed very little population differentiation, even between New Mexico and Utah populations.  Our results indicate that Flammulated Owls are wide-ranging with a large amount of intermixing between populations.  The combination of mark-recapture and genetic results suggest that this neotropical migrant has long-distance natal dispersal.

No extra-pair fertilization in Flammulated Owls despite aggregated nesting

We used DNA fingerprinting to estimate the frequency of extra-pair fertilization in the Flammulated Owl, a socially monogamous species often found nesting in aggregations. We observed owls  in aggregations of 3 to 10 territories with a mean nearest-neighbor distance of 539 m. Like other socially monogamous raptors, the Flammulated Owls we studied were genetically monogamous despite their relatively high breeding density. We suggest that the necessity of male parental care may be an important factor contributing to genetic monogamy in this species.

Differentiating nest sites of primary and secondary cavity-nesting birds in New Mexico

I assessed nest-site characteristics of two cavity-excavating species, Acorn Woodpecker and Northern Flicker, and two secondary cavity-nesting species, Flammulated Owl and Western Bluebird.  Woodpecker nests could be differentiated based on the tree species in which the cavity was excavated, the size of the cavity, and the forest structure around nests.  Flammulated Owls and Western Bluebirds nested in cavities excavated by both woodpeckers, but owls showed a preference for Northern Flicker cavities and bluebirds for Acorn Woodpecker cavities.  Owls used cavities that were larger and surrounded by denser forest than bluebird nests, and these differences could be partially attributed to the nest-site characteristics of excavator species.  My results emphasize the importance of considering communities of cavity-nesting birds for ecological studies and conservation efforts because of the interconnectedness of their nest use ecology.

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