Yep, it’s true. I didn’t think I’d ever see it—especially since I’ve harped on the sins of overgrazing as a chronic issue in quail management for most of my career. How can it be? After all, we haven’t had a cow on most of the ranch since 2007. But when you fly over it in a helicopter (as we did March 9 for our annual spring count) or as you try to entice the flames of a prescribed fire across a discontinuous fuel load, it’s painfully obvious. What can I say but “rats!”
Starting in the summer of 2015, we had a huge boom in our cotton rat population. We caught more “newly captured” cotton rats in the first week of trapping that summer than previous trapping seasons had caught all year. The population increased through the summer of 2016, and we had the largest cotton rat population on record. Why do we care? Cotton rats and other small mammals may act as a buffer for quail predation. They also have similar diets as quail, in addition to eating foliage and stems of plants. This led to the question, about how many rats did we have per acre? As an attempt to answer that question, I tasked technician Christine Palmer to estimate our “standing crop” of cotton rats during the boom. The following is her algorithm and logic.
When we trap at RPQRR, we set out a 5X5 grid of Sherman traps spaced about 10 meters apart (a grid encompassing about 1,600 m2). We put 5 of these grids in 8 different habitat types: CRP, food plot, riparian, prickly pear, rocky outcrops, sandy soil, old field, and mesquite woodland. To estimate how many “rats per acre” we had across the ranch, we first had to estimate how many rats we had per habitat type by using the Schnabel mark-recapture method. Then we had to determine the area we were sampling. The average home range for cotton rats is around 0.35 ha (0.86 acres) (Cameron and Spencer 1981), which equates to a 60-m buffer around the grid. Using this buffer and the known area of the grids, we calculated our effective survey area of 31.6 acres. We then estimated the number of cotton rats per acre, as follows:
||Rats per habitat (mark- recapture estimate)
||Rats per acre
After calculating the acres of each habitat type on the ranch (with ArcGIS), we extrapolated these estimates to indicate how many rats there were across the RPQRR (4,400 acres). Based on this methodology, we estimated 5.6 cotton rats per acre over the whole ranch. This allowed us to put into perspective just how high our rat numbers were. At 5.6 rats per acre, we estimate about 24,640 rats on RPQRR in the summer of 2016.
What role do these rats play on our quail populations? Are they a buffer species? Or could they be competitors of quail at these high numbers? In a way, cotton rats “graze” the landscape. They weave paths into the grass that became conspicuous in a “boom” cotton rat year. In theory, they may be reducing cover for quail or competing for food. However, little is known about the interactions between quail and cotton rats here on the “western front,” especially in years where both the quail and cotton rat numbers exploded. This would be a good topic for continued research— to be able to fully understand if cotton rats have a positive influence on quail survival or mortality, or if in fact they have a negative impact.
Reckon how many “animal-units” that 25,000 rats equates to? I couldn’t find any conversion factors from rats to AUs, so I arbitrarily said 100 rats/AU, which gives a “stocking rate equivalent” of 250 AUs, or a stocking rate of 1 AU per 17.6 acres. “Proper” stocking rate for cattle on this type of rangeland might be 35 acres/AU. With these assumptions, the RPQRR was “overstocked” pretty severely. Now, I hadn’t seen a rat boom like this one since 1992, so the overgrazing is acute, not chronic . . . a High Intensity – Low Frequency grazing system I reckon.
May be a moot point for time being, as our cotton rat abundance decreased by 97% from January 2016 to January 2017. Up to this point, our bobwhite abundance has tracked rodent abundance in a linear fashion . . . now that the cotton rats have crashed, we hope the quail don’t take a nosedive too. Stay tuned.
by Brad Kubecka, Graduate Research Assistant
Quail are sedentary birds, but in good years, displacement and dispersal are common. Old literature referred to these mass dispersals as “migrations,” and noted that they indeed coincided with years of extraordinary population abundance (Bennitt and Nagle 1937). This year we had multiple reports of bobwhites (and scaled quail) banded on RPQRR being harvested by hunters well off-site. Three instances stood out in particular as they were harvested in Kent and Jones counties up to 28 miles away (Figure 1). All of these birds were hatched in 2015, making them about 1.5 years of age upon harvest.
These reports mark our farthest documented dispersals from RPQRR, but aren’t unusual in the grand scheme. In 1968, a bobwhite banded by Val Lehmann and colleagues was harvested 65 miles south of the initial banding location only 2 months after being banded. In 1961, Campbell and Harris reported a scaled quail dispersing 61 miles.
Interestingly so, recent studies have found little variation in genetic diversity among 24 subpopulations of bobwhites in South Texas (Deyoung et al. 2012, Miller et al. 2012). This along with similar research findings in the southeastern United States (Evans et al. 2012) suggest that bobwhites have the ability to disperse much better than once thought.
Whether dispersal is good, bad, important, or indifferent depends on context. For example, we might prefer that birds stick around on a translocation site to establish a viable population. In 2013 and 2014, an estimated 90% of translocated bobwhites in the eastern Rolling Plains moved less than 2.5 miles from their release site (Downey et al.). This type of short-term site fidelity is what researchers like to see from a translocation effort. On the other hand, dispersal from productive populations can be extremely important for rescuing declining populations from extinction (Townsend et al. 2003, Sands et al. 2012). Dispersal distances typically depend on age with juveniles dispersing greater distances than adults (Fies et al. 2002). Fies et al. (2002) showed that juvenile males were more likely to disperse than any other age/sex group whereas adult males were the least likely to disperse. Townsend et al. (2003) did not document a differential proclivity to disperse among age/sex classes, but supported that juvenile dispersers moved significantly farther than adult dispersers. Cook et al. (2009) suggested that habitat quality dictated dispersal probability, but this effect depends on age. Old males in this study were more likely to disperse from closed canopy pine stands which are associated with poor quality habitat. Current evidence suggests dispersal does not influence survival, and that dispersers have higher nest initiation rates than that of non-dispersers (Townsend et al. 2003).
Though radio-telemetry technology has been a valuable tool for almost 4 decades, comprehensive dispersal information still lacks for bobwhites. With the arrival of new GPS technology in the past decade, it’s only a matter of time before researchers unravel just one more mystery in bobwhite ecology. Until then, we’ll rely on a much less expensive technology, i.e., aluminum leg-bands, as our “message in a bottle.” Currently we’ve leg-banded over 12,000 quail since 2008, and each increases our opportunity for a “return on investment.”
Knox Co. Blue Quail Restoration update
by Becky Ruzicka, doctoral student, Colorado State University
Last week we started trapping again to support the second year of our scaled quail translocation efforts in Knox County. We trapped two sites: one in the Rolling Plains Ecoregion and one in the Edwards Plateau. These birds were transported to the release site where they were placed in surrogators and will be held on site until their release in late-April. As part of this study we are comparing survival, reproduction, and dispersal of birds from different source populations (i.e., Rolling Plains vs. Edwards Plateau). We will also be evaluating the effects of a ‘soft release’ treatment to find an optimal amount of time to hold quail prior to release. A soft release means the birds are held on site for a length of time prior to release. Previous research has indicated that a soft release is preferable to a hard release (i.e., releasing birds immediately after capture) for scaled quail. For a comparison, this year we will release birds after holding them for 8 and 9 weeks, 4 and 5 weeks, and 1 and 2 weeks.
The scaled quail we released last year (393 in total) have exhibited survival and reproduction comparable to estimates of non-translocated scaled quail in the scientific literature. They have also exhibited a remarkable fidelity to the release site. Hens that had dispersed beyond our study site during the summer returned to the release site in the fall and several of them returned with chicks in tow. The first year’s results are encouraging to say the least. This year we hope to duplicate the effort in terms of number translocated.
Operation Idiopathic Decline: Search for the Smoking Gun
The role that disease and parasites may play in quail dynamics has been largely ignored since the 1920s. After the (in our opinion) inexplicable decline of quail in the Rolling Plains, the Board of RPQRF “got serious” about disease and funded a comprehensive project dubbed “Operation Idiopathic Decline.” Currently (as of Feb 2014), the RPQRF has invested $3.4 million into this ground-breaking study of disease and parasites. This webisode explains OID in more depth.