Birder's Guide

OCT 2014

Birder's Guide is the American Birding Association's newest publication. Each issue focuses on a key subject, providing tips from experienced birders on a wide variety of topics like Travel, Listing & Taxonomy, Gear, and Conservation & Community.

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Page 42 of 57

35 October 2014 | Birder's Guide to Listing & Taxonomy Natrona Heights, Pennsylvania Paul Hess casion as "the frst successful nesting by natu- rally occurring Aplomados in New Mexico— and the United States—in 50 years". But he also expressed concern that the proposed future releases of captive-bred birds of (relatively wet) tropical lowland origin into high desert grass- lands could threaten natural recolonization of the historic range by diluting the gene pool with birds unsuited to the new habitat. The 2002 nest by wild birds in New Mexico was the last of its kind known to be successful in the U.S. One factor in the decline is all too familiar in our time: degradation and loss of essential habitats, caused by human activities. In west Texas and New Mexico, native grasslands with sparse tree yuccas and other desert shrubs— key Aplomado habitat—have been ruined by overgrazing of livestock and by conversion to agriculture. In southern Texas, coastal prairies have been degraded or destroyed by extensive human development, and by succession from traditionally open grasslands to more dense brush inappropriate for the species. Compounding those disastrous effects on habitat are severe droughts, which have reduced the falcons' prey. Alberto Macías-Duarte and coauthors explain the complex ecological rela- tionships of drought, habitat, prey abundance, and reproduction in a detailed 2004 analysis (Auk 121:1081–1093). Another factor may have been the same hazard that so severely affected the Peregrine Falcon: contamination from toxic organochlo- rides in pesticides. Researchers in the 1970s found high concentrations of one such chemi- cal, DDE, in Aplomado Falcons from Mexico. DDE, a metabolic residue of DDT, accumu- lates in the food chain and is ingested via con- taminated prey. Reproductive failure is among the most notable of its damaging physiologi- cal effects. DDE in a female bird's reproduc- tive system causes abnormally thin eggshells, which are so weakened that they break. Lloyd F. Kiff, David B. Peakall, and Dean P. Hector compared Aplomado eggshells that had been collected in Mexico during the pre- DDT era with eggs they sampled there in 1977 when the long-lasting chemical was still pres- ent in the falcons' bodies. Eggs in the latter sample showed elevated levels of DDE and corresponding degrees of thinning similar to those documented for the Peregrine Falcon. Kiff and his colleagues published their fnd- This pair of Aplomado Falcons was photographed in coastal prairie off Texas Route 100 near Los Fresnos. This area and nearby Old Port Isabel Road are fairly dependable locations for birders to fnd the species. Photo © J. Marty Paige

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