Mexican jays (Aphelocoma wollweberi) prey on bats in Arizona.
Observations of Mexican jays preying on bats occurred in two different Mexican jay flocks around the South western Research Station in Portal, Arizona. The station is approximately 5,200 feet in elevation in Cave Creek Canyon of the Chiricahua Mountains. The riparian habitat in this area consists of oak-juniper-pinyon pine forest. These flocks are part of long-term studies on cooperative behavior (e.g., Brown and Brown, 1981), and the majority of local individuals are color-banded for unique identification. As such, I can say with confidence that two different individuals were involved in the observed bat consumption.
The first observation occurred on 26 May 2015 at 0755h (Pacific Standard Time). Through binoculars I observed a dominant male color-banded Mexican jay fly into an oak tree with an item in its mouth that was larger than commonly acquired prey. Upon closer inspection I determined it was a small bat with light golden fur and dark brown ears, wings, and face. This jay held the bat between its feet, pecked at it several times, and then pulled off pieces of flesh in a similar fashion to the way Mexican jays typically open acorns and large insects. The jay consumed some pieces of flesh, and cached other pieces in crevices in the tree. The processing of the bat continued for approximately 7 min, after which the jay flew off, leaving most of the bat carcass on the branch. Approximately 3 min later it returned and carried the remains of the bat out of sight. The remains were not identifiable to species, but given the size and coloration it is possible it was California myotis (Myotis californicus; Simpson, 1993), western small-footed myotis (Myotis ciliolabrum; Holloway and Barclay, 2001), or canyon bat (Parastrellus hesperus; Wilson and Reeder, 2005).
On 27 May 2015 around 1000h (Pacific Standard Time), I observed another dominant male jay from a different flock attack a similarly colored bat in the air. The jay flew toward and hit the bat with its feet while the bat was flying approximately 2 m off the ground. The bat fell to the ground and was struggling to fly off when the jay began pecking it repeatedly. For each strike, the jay stood on the ground approximately 15 cm from the bat, and then hopped in quickly to deliver a strong peck, somewhere on the bat's body. After fewer than 10 pecks, the jay picked up the bat and flew out of sight into a tree. When I followed and regained sight of the jay, it was eating the bat in the same manner as the jay had the previous day.
It could be relevant that in both observations it was a dominant male jay that executed the bat predations. Scramble competition assays (Brown et al., 1997) determined that these individuals are the most dominant in the social hierarchy of their groups. During breeding-season behavioral observations (Brown et al., 1997), I determined that these two jays were males. As such, it is possible that these two jays were comparatively larger in size, older, or more experienced foragers. More observations are needed, but it could be that only jays with these characteristics are able to catch evasively flying bats.
Previous records indicate that bird species, mainly raptors, comprise the taxon responsible for most observed bat predations (Sparks et al., 2000). So far only one other corvid species (Hoffmeister and Downes, 1964) and very few passerine species (Sparks et al., 2000; Estok et al., 2010) have been found to prey on bats. More observations are needed to determine the nature of encounters between these two taxa. For instance, it is unclear whether jays simply take advantage of chance encounters, or if they actively search out bat roosts, as has been documented with great tits (Estok et al., 2010) and several raptor species (Sparks et al., 2000). Predation resulting from opportunistic encounters is the most likely explanation if the individual bats observed in these two events were members of any of the three species mentioned above. All three species tend to inhabit daytime roosts singularly or in small groups at this time of year (Cross, 1965; Simpson, 1993; Holloway and Barclay, 2001). As such, it would be difficult and unrewarding for jays to search out roosting sites to prey upon bats. At the time of the observations, it is likely that Mexican jays were especially motivated to take advantage of prey encounters because caches have likely been depleted over winter, and arthropods are not yet very abundant (Brown, 1963). During approximately 65 h of subsequent observation on Mexican jays from June through October, no additional interactions with bats were observed, indicating that bat predation is not a prevalent foraging behavior in this population. Last, bats tend to be nocturnal or crepuscular, so it would seem that lack of overlap in activity patterns in these two taxa would limit interactions. However, numerous sightings of daytime flying bats have been reported, and suggest that insectivorous bats are occasionally active during the day to take advantage of additional food, or to drink water (Cross, 1965; Speakman, 1990, 1995). To better understand the impact of predation by Mexican jays on bat populations, more specific research needs to be conducted to determine seasonality and frequency of daytime flying in these three bat species in Arizona.
I thank the National Science Foundation Graduate Research Fellowship Program for funding. I thank J. J. Valente, R. R. Ha, and anonymous reviewers for commenting on this manuscript. Additionally, I thank R. Torres for Spanish translation. Finally, I thank the Southwestern Research Station staff and the American Museum of Natural History; as well as P. Jablonski, S. I. Lee, and J. Eimes for support and jay banding activities at this research location.
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Submitted 2 December 2015. Acceptance recommended by Associate Editor, Eddie Lyons, 23 February 2016.
Kelsey B. McCune
Department of Psychology Box #351525, University of Washington, Seattle, WA 98195
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|Author:||McCune, Kelsey B.|
|Date:||Jun 1, 2016|
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