Does touching a bird's nest cause the female to abandon it?

(Male Bobolink.  The male usually helps at the nest, but the female does most of the work.)

Did you grow up with your mother telling you not to touch that robin's nest because the mother would not come back and the babies would die?  Most of us did.  This has to be one of the most frequently uttered adages in all of nature lore.  The fact is, this is mostly myth.

During the 1980s, Eric Bollinger and I studied Bobolinks in upstate New York.  Bobolinks are a polygynous (i.e., males commonly have more than one female mate) species in the blackbird family.  The males have an incredibly long, bubbly song and their appearance is described as having  a tuxedo on backwards.  They are about the size of a sparrow.  Bobolinks build their grassy nest on the ground.  The female lays one egg per day until she has completed a clutch of five, begins incubating with the laying of the penultimate egg (next to last), incubates the eggs for 10-12 days, and then feeds her nestlings for another 10-12 days until they fledge.  Males usually help feed nestlings, but they are not as attentive as females.

Eric and I and our technicians located hundreds of Bobolink nests in those years, which are built on the ground in hayfields and meadows.  Once we located a nest, we placed a bamboo stick in the ground about a meter away from the nest with some colored plastic flagging on the top of the stick so we could relocate the nest at will.  Once found, we checked the contents of the nest every day to determine its progress and success.  When the nestlings were about 7 days old, we removed each one from the nest, collected a blood sample, measured it, placed an aluminum band on one leg, and returned it to the nest.  In some years, we removed the eggs and measured them before returning them to the nest.  In other words, we disturbed the nests a great deal during their three-week life, although we were careful not to trample the concealing vegetation around the nest any more than absolutely necessary.

Nearly 1,000 nests endured this harassment, and Eric and I learned a great deal about the behavior of  females because of it.  If we found a nest while the female was constructing it, she usually abandoned the nest.  If we found the nest when she had laid only 1-2 eggs, she often abandoned the nest.  Once the female had laid her full clutch of eggs and began incubating, she almost never abandoned, and if the nest contained nestlings, she would absolutely never abandon her brood.  The same seems to be true of most other birds as well.

Think of it this way: the more the female had invested in time and energy in the whole operation, the less likely she was to give it up.  Remember also, most birds have only a limited seasonal window during which they can successfully complete the nesting cycle.  In the case of Bobolinks, it takes a total of about 30 days from initiation of nest-building to fledging of their young.  In addition, they continue to feed their fledglings after they leave the nest for some period of time.  Bobolinks do not return from South America until early May and they start moving south again in August.  If they had to start over with the nesting cycle part-way through, they would barely have enough time to get those babies to a size and age where they could endure a long migration at the end of the summer.

Realize that the patterns I have described above probably apply to most songbirds in North America.  They may not apply equally well to tropical birds, which live in an area with many predators, and which always seemed to me to be extremely wary of predation threats.  Those species might abandon their nests more readily than temperate species.

So when your mother or grandmother tells you not to touch that nest because the female will not come back to it, you can say: "Well Mom, it goes like this".  There is a danger of attracting predators to a nest that you have disturbed, and where you have presumably left your scent.  Raccoons are very good at following these clues.  But as far as the female of the nest is concerned, she has invested too much for too long to walk (well, or fly) away easily.

The phoebe and the porch light

 (An Eastern Phoebe with an insect.  Is it the same bird nesting on my porch light year after year?)

Each year in late March, Eastern Phoebes (Sayornis phoebe) return to my property from having spent the winter as far south as Mexico.  Today, they returned.  I can always tell, because the male sings incessantly when he returns, and his favorite song perch seems to be at the corner of our house next to our bedroom.  The singing starts just before it is light, so spring phoebes and DrTom are on the same schedule, fortunately.  I love early morning.

Bird migration has always fascinated me.  I have been more interested in why birds migrate, than in how they do it.  The answers to the how question are truly astounding, and there are many good summaries of this.  Much of the early pioneering work on this topic was done at Cornell University by Bill Keeton, who used homing pigeons as his model.  And the Germans Kramer, Sauer, and Wiltschko are important.  Depending on the species, they might use visual landmarks like rivers during the day, or they use the sun’s location, or they navigate at night by orienting to the stars, or they use the earth’s magnetic field.  Bobolinks (Dolichonyx oryzivorus), for example, contain small deposits of an iron compound called magnetite in their skulls.  This is presumably used to detect the weak forces of the earth’s magnetic field to help them migrate between North and South America.

Eric Bollinger and I published a number of papers in the 1980s on Bobolinks and the behavior known as breeding site fidelity, or breeding site faithfulness.  This is the tendency of individuals to return to the exact location where they bred the year before.  It turns out that this is a common phenomenon in migratory songbirds: adults often return to the exact location where they bred the year before, but their babies rarely return to the place where they were born.  In Bobolinks and most songbirds where this has been studied, adults tend to return to the site where they bred the year before if they were successful in producing babies at that location.  If the nestlings had been eaten by a snake or a skunk, for example, or the nest was destroyed by farming equipment, then those adults tend not to return to the same location the following year.  It appears there is a simple Darwinian algorithm operating in those pea-sized brains: if I was successful in producing offspring, return; if I was unsuccessful, do not return.

So, every year since 1980 we have had a pair of Eastern Phoebes near our home.  But the observation is more remarkable than that.  Phoebes originally nested on ledges beneath an overhang, probably rocky cliffs.  Houses, however, are a great substitute, because of the overhanging eaves and the existence of some kind of platform beneath that overhead protection—like a window ledge.  At our home, phoebes almost always use the light fixture next to the front door.  (They also use a window ledge on the back of the house.) This is convenient for me, because every morning during the breeding season, I step outside, reach my hand up and into the nest, count the number of eggs or nestlings by feel, and then resume drinking my Cafe Britt coffee (which, by the way, you can buy on this site).  Although I have never formally studied phoebes, this would make for pretty easy field work.  The bottom line is that nearly every year, the nest over our light fixture successfully fledges 4-5 young.

Now, I have never banded the phoebes at my house, and this is unfortunate.  I am missing a lot of the biological story, because I do not know if these are the same individuals that return to my property each year.  But for 28 years, phoebes have nested on this light fixture and yet these birds probably live only a few years—they can not be the same individuals during all of that time.  This means that new birds sometimes settle near my house, start looking for a suitable nest site, see the light fixture under that overhang, and a “CFL light bulb” goes off in their little head.  (Research has proven that light bulbs in bird heads are fluorescent and not incandescent).  Each succeeding generation of phoebes spots that nest location and simply can not resist it, in spite of the fact that every time we enter or leave the front door, the attending adult is flushed off the nest.

As you can see, my original interest in site fidelity has blended with a fascination for this incredible innate focus by the bird on a suitable resource, in this case a nest site.  I am sure that exactly the same consistency and skill go into locating and capturing food—phoebes mainly eat flying insects like moths.  Many thousands of years of natural selection have honed these abilities into a razor-sharp performance, which ensures their survival and successful reproduction.  For me, spring has not really started until I hear that simple, yet distinctive song of the phoebe.  My coffee is ready, so all I need now is this year’s nest.