NAV MAP - Experimental System Analysis of the Pigeons Navigational Map:

Project Outline:

NavMap will apply novel analytical techniques in combination with experimental manipulation of navigational factors to investigate the cues with which birds navigate. To investigate this we will use homing pigeons, famous for their ability to home successfully from far away and unknown places. First scientific research into the pigeon’s ability to navigate dates as far back as 150 years, but we still don’t fully understand how they achieve their feats of navigation. According to our current understanding they appear to navigate using a two step process - utilizing a map and a compass. Although huge strides have been made in our understanding of the underlying compass component of this process - now garnering interest from a wide variety of different fields, such as chemistry and quantum physics - the second component, the map step is still poorly understood. In the past, experiments produced conflicting reports on effects of individual experimental treatments when attempting to investigate specific sensory cues. If anything these past experiments already hint at a rather complex system involving multiple redundant cues, but how these integrate, and how removal of individual cues effects the performance as a whole, is still unclear. Recent developments in mathematical analysis of GPS tracks have not only provided direct evidence for this, but have also produced new methods, that allow a direct look at the underlying mechanisms of the navigational process. Rather than estimating the pigeon's navigational ability based on indirect measurements of performance, we can now directly measure the impact of any experimental treatment on the whole navigational process. In this project we will combine these new methods, with experimental treatments to investigate in detail the involvement of individual sensory modalities in the pigeon’s navigational process.

Current Research Topics:

Is the formation of habitual routes a reliable indicator for piloting?

Reanalysis of pigeons treated with a short, but strong magnetic pulse.

Manipulation of the magnetic sense through application of bar magnets.

Background:

In the past I have, in cooperation with researchers from the university of Frankfurt, investigated the underlying processes of navigation in homing pigeons. Utilizing new methods, based on the principles of dynamic systems theory, we have been able to determine the number of factors, which are involved at any given time during a pigeons journey home, allowing us to directly measure the influence of experimental conditions, experience and the general area on the actual navigational process.

Properties of the Navigational Process:

In a novel approach, using the so called method of time lag embedding, we analyzed the tracks of pigeons recorded with the help of miniaturized GPS recorders. We calculated two variables, the largest Lyapunov exponent to determine the predictability of the underlying process and the correlation dimension to estimate the number of factors involved.

The navigational process is almost deterministic and at least four independent factors are involved in the underlying process (figure shows a phase space representation - the so called attractor - of the navigational process). Additional factors, as indicated by an increase in the correlation dimension, seem to be included as the pigeons approach their home loft. These findings suggest that the underlying cognitive process is highly flexible allowing individual navigational factors to be included as required and weighted independently. Neither the correlation dimension nor the Lyapunov exponent are affected by increasing familiarity of the pigeons with the terrain. This suggests that the same process controls flight across familiar as well as unfamiliar terrain. More information is available here

Navigational Factors: The Sun Compass

We analyzed GPS-recorded tracks of clock-shifted pigeons from six release sites to determine how the conflict between their sun compass and other navigational cues affects the underlying navigational process.

The short-term correlation dimension, a parameter that reflects the complexity of the navigational system, and with it, the number of factors involved, is affected by the conflict between the sun compass and other navigational cues. At the release site there were no detectable difference in short-term correlation dimension of controls and clock-shifted pigeons. After leaving the site, until reaching their homeloft, clock-shifted pigeons had a significantly lower short-term correlation dimension compared to the controls. While this difference was small, it was consistent, and suggests a different rating and ranking of navigational cues. It appears that the clock-shifted pigeons did not simply ignore the information from their manipulated sun compass, but downgrade it in favour of other cues, like their magnetic compass. This is supported by the finding that throughout the entire flight, even close to their homeloft, clock-shift pigeons continued to show deviations in their heading in the expected direction. More information is available here

Development of the Navigational Map:

We analyzed GPS-recorded tracks from pigeons of different age from 11 sites between 3.6 and 22.1 km from their home loft

Changes occur in the navigational system as the birds grow older and became more experienced (See figure on the left, with the upper set of tracks from adult pigeons and the lower set of tracks from juvenile pigeons; Note, both, the difference in directness of the tracks and the difference in correlation dimension). The efficiency of juveniles in their 1st year of life, with only 0.27, was rather low, indicating that the young birds covered more than three times the direct distance home. In the second yearthe efficiency of the same birds increased up to 0.80 and was no longer different from that of older pigeons. The short-term correlation dimension, a variable that reflects the number of factors involved in the navigational process, also increased with age. In juveniles, it is markedly lower than in the other two groups, but even in yearlings, it is still significantly lower than that of old pigeons, indicating that the navigational map of the yearlings is developing further. Our results indicate that the map system, although functional in the first year of life, continues to be become more complex: - older pigeons seem to either consider more navigational factors than younger ones or at least weigh the same factors differently. More information is available here