Current Research

Synergistic effects of food and predators on the population viability of songbirds.

Most animals must continually balance the need for food against becoming food. Hence,food and predators are unlikely to have independent effects on demography. Because population level experiments on terrestrial vertebrates are rare, and bifactorial experiments are rarer still, synergistic effects of food and predators on demography have only recently been shown in mammals and have never before been demonstrated in birds. My current research provides the first evidence of just such synergistic effects in birds.

Synergistic Effects in Birds

These results confirm conclusions from my earlier work on the respectiveroles of forest fragmentation, and Brown-headed Cowbirds, in songbird declines, and help to explain why declines are both so common and so precipitous. Sinceanthropogenic disturbance both reduces food availability and increases predation, it followsthat natural systems must generally possess both more food and fewer predators. Whenthese natural systems are disturbed, precipitous declines are to be expected if a there is a negative synergism between food shortage and increased predation, and either foodor predation changes. A fuller understanding of such synergistic effects is essentialif we hope to prevent further declines, and reverse existing ones.

Graduate student Marc Travers commutes to work

My current major research program involves an ongoing 2x2, manipulative foodaddition plus natural predator reduction experiment on 14 populations of Song Sparrows (Melospiza melodia). Each site is home to about 7 territorialpairs. Six sites are located in Victoria, B.C., where predators are abundant, and the remaining 8 arelocated on several small islands (in the adjacent Haro Strait), where predators are rareor absent. From Feb.-Aug. food is added ad libitum to half (3) of the high predatorand half (4) of the low predator sites. A single gravity fed feeder filled with a mixtureof millet seed and high protein pellets is located in the middle of each territory at the foodsupplemented sites. All 14 Song Sparrow populations are intensively monitoredthroughout the 7 mo. breeding season. Breeding success is established by finding every nestbuilt by every territorial pair as early as possible in the nesting cycle and conductingfrequent nest checks thereafter to accurately determine the pattern of nest failures and the proximate cause (abandonment, starvation or predation).

Fed and control sites in low (Portland Isl.) and high (Victoria) predator areas

On average territories subject to the combined food addition + low predator treatment fledge almost twice (1.7 times) as many young as would be expected if theeffects of food and predators were independent and additive. This effect (1.7 >additive) is similar in scale to those (1.5-1.9 > additive) recently shown in mammals.

Balancing food and predator pressure induces chronic stress in songbirds.

Chronic physiological stress induced by the never-ending tension between finding food and avoiding predators appears to be the proximate mechanism underlying the above synergistic effects on demography. The ‘chronic stress’ hypothesis predicts: 1) an animal’s stress profile will be a simultaneous function of food and predator pressures given the aforementioned tension; and 2) these inseparable effects on physiology will produce inseparable effects on demography due to the resulting adverse health effects. Working with Prof. Michael Clinchy (UVIC), Prof. Rudy Boonstra (U of T) and Prof. John Wingfield (U Washington) we have now documented the simultaneous food and predator effects on measures of chronic stress predicted by the 'chronic stress' hypothesis. Chronic stress appears to provide the missing link between immediate behavioural and longer-term demographic processes.

This work was featured in the Globe and Mail, National Post and on CBC webnews.

Professors Mike Clinchy and Rudy Boonstra stressing out on the Gulf Islands

Mobile Solar Video (MSV) systems for wildlife surveillance.

A chronic problem facing anyonestudying the 90 % of vertebrates that are small and secretive is that while the effect of predation is easily measured we rarelyactually know who the principal predators are. The development in just the past few years of miniaturized systems that allow us to 'catch predators in the act' is assignificant an innovation for ecology as the development of the microscope was for the study of disease. Technical constraints, however, have so limited the use of these systems that only one study has generated enough data for statistical analyses. While working with me as a post-doc, and using funds from a Canada Foundation for Innovation (CFI) grant on which I acted as PI, Prof. Michael Clinchy (UVIC) developed 8 Mobile Solar Video (MSV) systems designed to permit 24 hr/day, continuous video surveillance of wildlife, over a 20 ha area, at remote locations anywhere in Canada. The picture below is from a video clip you can watch using Windows Media Player. In this video the song sparrow mom tries to defend her nest against a female brown-headed cowbird. There are 2 eggs to start with, 1 of which the cowbird tries to toss. When the cowbird leaves, there are 3 eggs. So in less than 10 seconds the cowbird has punctured a sparrow egg and laid her own all while being attacked by the song sparrow mom.