Variation in Prey Delivered to Common Black-Hawk (Buteogallus anthracinus) Nests in Arizona Drainage Basins
Understanding how raptor diets vary across local and regional scales can be important when human actions have the potential to alter prey abundances. We combined data on prey delivered to 16 Common Black-Hawk (Buteogallus anthracinus) nests in three tributaries of the Verde River, Arizona, in 2008 and 2009 with similar data reported previously (1994) for three other Arizona drainage basins to better understand variation in diet composition within and across drainage basins. Within the three drainage basins studied in 2008 and 2009, nests clustered into two groups: those along Fossil Creek, where fish and amphibians were common, and those in Wet Beaver and Oak Creek drainage basins, where reptiles and nonnative crayfish were more abundant. When data from all six drainage basins were combined, drainage basins again clustered into two groups, with prey deliveries in one cluster dominated by fish and amphibians and in the other cluster by reptiles. These results confirm the opportunistic nature of prey use by Common Black-Hawks and highlight the variation in diet that can occur both within and among drainage basins. Management targeting the eradication of nonnative crayfish or the reintroduction of native amphibians and fish could alter prey availability for this raptor species. Entender cómo varía la dieta de rapaces a lo largo de escalas locales y regionales puede ser importante cuando las actividades humanas tienen el potencial de alterar la abundancia de presas. Combinamos datos de presas provistos a 16 nidos de Buteogallus anthracinus en tres tributarios del Río Verde, Arizona, en 2008 y 2009 con datos similares reportados previamente (1994) en otras tres cuencas de drenaje de Arizona, para entender mejor la variación en la composición de la dieta dentro y a lo largo de las cuencas hidrográficas. Dentro de las tres cuencas estudiadas en 2008 y 2009, los nidos se agruparon en dos: aquellos a lo largo del Fossil Creek, donde los peces y anfibios fueron comunes, y aquellos en las cuencas de Wet Beaver y Oak Creek, donde los reptiles y los cangrejos exóticos de río fueron más abundantes. Cuando se combinaron los datos de las seis cuencas, éstas se agruparon en dos, con la provisión de presas en un grupo dominada por peces y anfibios y en el otro por reptiles. Estos resultados confirman la naturaleza oportunista de uso de presas de B. anthracinus y resalta la variación en la dieta que puede ocurrir dentro y entre las cuencas hidrográficas. El manejo enfocado en la erradicación de los cangrejos exóticos de río o la reintroducción de anfibios y peces nativos podría alterar la disponibilidad de presa para esta especie rapaz.Abstract
Resumen
UPGMA tree based on similarity in composition of prey brought to Common Black-Hawk nests at 16 nests in three drainage basins in Arizona, U.S.A., in 2008 and 2009. Prey categories depicted include nonnative crayfish (black), fish (white), amphibians (light gray), reptiles (dark gray), and birds and mammals combined (horizontal stripes). Letters and numbers immediately below the cluster diagram correspond to each nest, with their position within each drainage depicted to the right. Smaller circles and letters with superscripts indicate nests studied in both years that were likely the same pair of hawks. Numbers below nest designations in the cluster diagram represent the number of young ultimately fledged from that nest, with asterisks indicating nests exhibiting brood reduction. Fish and amphibians were significant indicator species for the three Fossil Creek nests (lower right), whereas reptile and crayfish were significant indicator species for the remaining nests in Wet Beaver Creek (middle) and Oak Creek (upper) drainage basins. Within the Wet Beaver/Oak Creek cluster, two nests in upper Oak Creek (A and B) were distinguished by lack of crayfish and had mammals as significant indicator species, whereas all other nests had crayfish as the significant indicator species.
UPGMA tree based on similarity in composition of prey brought to Common Black-Hawk nests in six drainage basins in Arizona, U.S.A. Prey categories are as described in Figure 1 except for birds (dots) and mammals (horizontal stripes). Drainage basins include three studied in 2008 and 2009 (A = Oak Creek, B = Wet Beaver Creek, C = Fossil Creek) and three studied previously by other authors (D = lower Verde River, E = Aravaipa Creek, and F = Burro Creek; reported in Millsap 1981, Schnell et al. 1988, Schnell 1994). Numbers in parentheses represent total number of nests monitored in that drainage. Reptile and crayfish prey categories were significant indicator species for the upper cluster, whereas fish and amphibians were significant indicator species for the lower cluster.
Contributor Notes
Associate Editor: Joseph B. Buchanan