Report to the National Birds of Prey Trust

2 February 2008

Our previous work (Rudnick et al. 2005) on Imperial Eagles (Aquila heliaca) from north-central Kazakhstan illustrated how non-invasively sampled feathers can be used as a source of DNA, which can serve as a unique genetic “tag” that allows reliable individual identification.  There, we characterized the site fidelity of breeding pairs, their mate fidelity, and population turnover.  These data allowed us to begin preliminary calculations of annual adult survivorship and reproductive rates within the Naurzum Zapovednik (a national nature reserve).

The funds from NBPT have supported 1) continued research on the adult breeders in an effort to improve our estimates of turnover and sustainability and 2) an initial characterization of the non-breeding (floater) population. 

Breeders
Long-term breeding territories within Tersec and Sipsin forests (Naurzum Zapovednik) were sampled for naturally shed adult feathers.  At the onset of the 2006 breeding season, an average of ten feathers were sampled and genetically analysed from each of nine nests in Tersec (a mostly coniferous forest) and five nests from Sipsin (a deciduous forest).  DNA was extracted from the tip of each individual feather and each was genotyped at seven highly variable microsatellite loci.  Multilocus genotypes were assigned to each analysed feather, which were used to construct genetic tags for each individual sampled (Rudnick et al. in prep).  These genetic data from 2006 allowed us to evaluate allowed direct comparison to genotypes previously detected among eagles sampled from the Zapovednik from 1999 - 2002. 

The results from this study will be published in a peer reviewed paper. However, a brief summary is as follows. A maximum of two adults were present at all but one of the fourteen nesting sites and none of the adults were present at >1 nest during a breeding season.  The outlier nest (IE50 from Tersec) was visited by at least nine different eagles during 2006, and none of these nine were genotyped previously.  This nest likely was abandoned some time ago and may now be a roosting site for unmated (or “floater”) eagles.  Adult turnover rates at the remainder of nests varied between areas and across years.  Observed turnover between 2006 and 2002 sampling was ~12.5% at Tersec, 70% at Sipsin and ~35% overall. 

On average, adults paired with the same partner and annually returned to the same nest for 5 consecutive years.  Thus there is some indication that serial monogamous pairs retain particular nests over several years.  Yearly turnover at nest sites mostly involved replacement of one partner (no apparent sex bias) but occasionally both adults were replaced by a new breeding pair.  Turnover involved replacement by both previously undetected and previously replaced (from other territories) adults. The presence of reoccurring breeding adults across years may indicate that available nest sites (and therefore breeding opportunities) are monopolised by particular dominant individuals within the population.

Nonbreeders
In addition to our work on the breeding population, we have used noninvasively collected feathers to profile nonbreeding “floaters”.  At the Naurzum Zapovednik, scores of floaters were known to use communal roosts but little else was known—other than the fact that several species (Imperial Eagle, Golden Eagle, and White-tailed Sea Eagles) occasionally roosted together.  Thus, our first task was to determine the “donor” species for each feather.

Genetic analysis of noninvasively collected bird feathers is of growing importance to avian ecology; however, most genetic studies that utilize feathers make no mention of the need to verify their species of origin.  While plumage patterns and collection location often are indicative of species identity, broad-scale feather collections may require definitive species identification prior to analysis.  Genetic species identification has been applied to noninvasively collected samples from a wide range of taxa but, to date, these techniques have not been widely used on bird feathers.  We developed and tested a PCR-based technique for identifying eastern Imperial Eagle samples among a vast number of noninvasively collected feathers.  Species identification was accomplished by amplifying a fragment of the mitochondrial cytochrome c oxidase I gene, then digesting that fragment with a restriction enzyme.  The resulting species-specific restriction fragment length polymorphisms (RFLPs) were easily visualized by gel electrophoresis.  We tested this PCR-RFLP assay on over 300 individuals that had been genetically identified from noninvasively collected feathers and demonstrated that the assay is both reliable and robust for DNA of low quality and quantity.  The genetic methods of species identification used to develop this assay can readily be applied to other bird assemblages, making them particularly relevant to a broad range of future avian research.

After identifying the donor species for each feather, we focused on Imperial Eagle samples to study non-breeders.  While the pronounced territoriality of breeding adults facilitates behavioral studies, the demography of non-breeding individuals (pre-adults and non-territorial floaters) was almost completely unknown.  Traditionally, limited data on pre-adult and floater movement come from wing-tagging and/or telemetry studies.  We used genetic analyses of noninvasively collected feathers to investigate the population biology of non-breeding eastern Imperial Eagles in Kazakhstan.  Microsatellite profiles of shed feathers indicated that eastern imperial eagles roost communally with other raptors.  Furthermore, roosts were large and dynamic:  287 non-breeding eastern imperial eagles were detected in our sample, and a mark-recapture analysis estimated the total number to be 308 ± 8.  The natal origins of these individuals were investigated by comparing their microsatellite profiles to those available for >90% of the eastern imperial eagle chicks hatched at the study site over the six previous breeding seasons.  Only 4% of the individuals genetically matched a chick, suggesting that the reserve may serve as a critical refugium for pre-adults and itinerant floaters.  Feathers have long been recognized as a suitable source of DNA, but few studies have used wide-scale, noninvasive collections of feathers (>1000 samples) to investigate fundamental aspects of avian biology.  Our research demonstrates that noninvasive genetic analyses of feathers can be used to evaluate population size, natal philopatry, and local movements of birds that are difficult to study using traditional means.

This research was greatly facilitated by financial support from the National Birds of Prey Trust.

T. Katzner (National Aviary)
D. Gopurenko and J.A. DeWoody (Purdue University)

For more information about the findings of this project, please click here