Birds of southeast Texas in photos

Keep the lights down low and hang feeders if you want the local birds to sleep in.

“In comparison to chemical and noise pollution, light pollution is more subtle, and its effects have perhaps not received the attention they deserve,” said Bart Kempenaers of the Max Planck Institute for Ornithology in Germany. “Our findings show clearly that light pollution influences the timing of breeding behavior, with unknown consequences for bird populations.”

The researchers investigated the effects of artificial night lighting on dawn song in five common forest-breeding songbirds. In four of those five species, males near street lights started singing significantly earlier in the morning than did males in other parts of the forest.

Further study of the effects of that behavioral shift on blue tits based on comparison of their reproductive behavior with and without street lights over a 7-year period showed real consequences. Females near street lights laid their eggs on average a day and half earlier. And males near lights at the forest’s edges were more successful in attracting “extra-pair mates,” meaning that they more often sired offspring with females other than their primary social partners.

That might sound like a bonus for those males, but Kempenaers said that doesn’t mean it’s good for the species, and it might not even be good for the males in question. read more

Feeding wild garden birds during the breeding season may delay the start of the dawn chorus sung by some species, say researchers.
Their study claims to have found a link between supplementary feeding and the observed changes in songbird behaviour.
The scientists made the discovery studying populations of great tits living in the suburbs of Oslo, Norway.
Birds with access to feeders delayed their song by up to 20 minutes, often beginning only after the sun had risen. Feeding garden birds such as tits delays dawn chorus

More information:

Wild bird feeding delays start of dawn singing in the great tit

Artificial Night Lighting Affects Dawn Song, Extra-Pair Siring Success, and Lay Date in Songbirds

Some birds can see magnetic fields like we see colors. Those with sharp vision see the field clearly, those with impaired vision have trouble same as we might reading small print in our later years.

Some birds can sense the Earth’s magnetic field and orientate themselves with the ease of a compass needle. This ability is a massive boon for migrating birds, keeping frequent flyers on the straight and narrow. But this incredible sense is closely tied to a more mundane one – vision. Thanks to special molecules in their retinas, birds like the European robins can literally see magnetic fields. The fields appear as patterns of light and shade, or even colour, superimposed onto what they normally see.
Katrin Stapput from Goethe University has shown that this ‘magnetoreception’ ability depends on a clear image from the right eye. If the eye is covered by a translucent frosted goggle, the birds become disorientated; if the left eye is covered, they can navigate just fine. So the robin’s vision acts as a gate for its magnetic sense. Darkness (or even murkiness) keeps the gate shut, but light opens it, allowing the internal compass to work. Read more Robins can literally see magnetic fields, but only if their vision is sharp

More information:
Magnetoreception of Directional Information in Birds Requires Nondegraded Vision (paper $)

Even tiny patches of woods in urban areas seem to provide adequate food and protection for some species of migrating birds as they fly between wintering and breeding grounds, new research has found.

The results are important because, with the expansion of cities worldwide, migrating landbirds increasingly must pass through vast urban areas which offer very little of the forest habitats on which many species rely.

“The good news is that the birds in our study seemed to be finding enough food in even the smaller urban habitats to refuel and continue their journey,” said Stephen Matthews, co-author of the study and a post-doctoral researcher in the School of Environment and Natural Resources at Ohio State University.

Matthews conducted the study with Paul Rodewald, an assistant professor of environment and natural resources at Ohio State.

The researchers published two related studies: one will appear in an upcoming issue of the journal Landscape Ecology and the other appeared in a recent issue of The Condor.

Both studies involved a secretive relative of the American Robin called Swainson’s Thrush (Catharus ustulatus). Swainson’s Thrushes winter mainly in Central and South America, and travel through the eastern United States to their breeding grounds in the boreal forests of Canada.

The researchers captured up to 91 Swainson’s Thrushes at a woodlot on the Ohio State campus while they were migrating through Columbus in May or early June, 2004 to 2007. They then fitted them with tiny radio transmitters and released them at one of seven wooded sites in the Columbus area. (The radio transmitters were glued to back feathers and naturally fell off within a few weeks.)

The sites had forest sizes that ranged from less than one hectare (1.7 acres) to about 38 hectares (93.9 acres) in size.

Using the radio transmitters, the researchers tracked how long the thrushes would stay in the woodlots where they were placed. If they left soon after release, that would suggest that the sites did not provide the food and habitat that they required.

Results showed that at the five largest release sites, all the birds stayed until they left to continue to their migration north. At the two smallest sites (0.7 and 4.5 hectares), 28 percent of the birds moved to other sites in the Columbus region.

“The fact that a majority of the birds stayed at even our smallest sites suggests that the Swainson’s Thrushes were somewhat flexible in habitat needs and were able to meet their stopover requirements within urban forest patches,” said Rodewald, who also has an appointment with the Ohio Agricultural Research and Development Center in Ohio State’s College of Food, Agricultural, and Environmental Sciences.

The study revealed that the birds stayed at each site from one to 12 days, with the average being about four days. There was no difference in how long the thrushes stayed across the seven sites.

“If our study sites differed strongly in habitat quality, we should have seen differences in how long the birds stayed,” Matthews said. “The fact that the stopover duration was similar suggests that all the sites were meeting the needs of the thrushes as they prepared for the next leg of migration.”

The study did find that the later the calendar date, the shorter the thrushes stayed at the sites. That may be because the later-arriving birds would be in more of a rush to reach their breeding grounds, Matthews said.

Weather was also a factor: birds tended to leave the sites when winds were light, following a drop in barometric pressure.

Birds also tended to stay longer if they had lower body mass, suggesting they needed to bulk up more to continue their journey.

While nearly all sizes of woods appeared adequate for the thrushes, they still seemed to prefer larger forested areas, the study revealed.

In one of the studies, the researchers found that in the larger urban woodlots, the thrushes would stay farther in the interior and not get as close to the forest edge. The birds also moved less during a three-day period in the smaller sites, indicating they were more restricted in the area where they could forage for food.

The researchers cautioned that this study was done with just one species, so it is impossible to say whether the results will apply to other species. But the Swainson’s Thrush is one of the more forest-sensitive species, so the fact that it could make do with even small, fragmented woodlots is encouraging.

“These findings suggest that remnant forests within urban areas have conservation value for Swainson’s Thrushes and, potentially, other migrant landbirds,” Rodewald said.

“Obviously, larger forest patches are better, but even smaller ones are worth saving.”

The study was funded by the Ohio Division of Wildlife.

Read more

Papers:
Urban Forest Patches and Stopover Duration of Migratory Swainson’s Thrushes ($)
Movement behaviour of a forest songbird in an urbanized landscape: the relative importance of patch-level effects and body condition during migratory stopover ($)