Thursday, November 29, 2012

Which Jackrabbit?

White-sided Jackrabbit (Lepus callotis) photo from wickimedia commons. Note the black on the inside of the ears.
A couple of years ago Charlie O'Brien and I were traveling through the San Rafael Valley close to the tiny town Lochiel at the Mexican border when suddenly two hares came racing across the undulating grassy hills. They were chasing each other the way courting hares do, flinging themselves high into the air and thus overtaking each other in the vertical rather than the horizontal plane. Even from a distance of several hundred feet we could see that they each had a large white area on their flanks. A year later I was returning with Eric Eaton from a bug-party in Sierra Vista, so it must have been in late August. We took the long way home, around the Chiricahua Mountains and, at dusk, were just turning north again in the Canelo Hills. Landscape-wise the area is the northern extension of the San Rafael Grasslands. We may have even been talking about my earlier observation. At any rate, we saw another Jackrabbit with white flanks. Eric got out of the truck and followed it for a while to get some photos. I had only my 50mm macro lense, so I didn't even try. I never saw the result of this pursuit, but I think it was already too dark to shoot a moving target.

I was reasonably sure then that the hares we saw on both occasions were white-sided jackrabbits (Lepus callotis) also known as the Mexican hares. Literature gives Northern to Central Mexico and Hidalgo County in SW New Mexico as the distribution range of this threatened species. But occurance in Arizona is assumed possible but has not been clearly recorded. So did we actually see L. callotis?

The two other possible species are Black-tailed  and Antelope Jackrabbit, and both are widespread and common in Arizona.

 Watercolor of Black-tail Jackrabbit under Creosote bush with dry Cheat Grass. by Margarethe Brummermann  
On our property in Picture Rocks, Arizona, we regularly see the Black-tailed Jackrabbits (Lepus californicus). Especially the youngsters that congregate to drink at our bird bath are literally 'all ears'. They can use these huge appendices for heat dissipation, and when it's hot, a bright pink glow from expanded blood vessels makes the ears look even more impressive. They feed on anything here. They clipp creosote branches, graze on cheat grass, love cactus fruit whose seeds they distribute undigested in their pellets. When a barrel cactus falls over and exposes its thornless underside, a Black-tailed Jackrabbit can hollow it out in a single night. Only a huge pile of pellets will stay behind.


Like the White-sided Jackrabbits, they have black areas on the tips of the ears, but on the outside, and black tails. But their flanks are tan colored like the rest of the upper side of the body. This JR has a wide distribution range, including all of the Southwestern US, east to Missouri, north to Nebraska and Washington and south into Mexico. 


Antelope Jackrabbit (Lepus alleni)  Photo by Eirini Pajak
The other Arizona species is the Antelope Jackrabbit (Lepus alleni). I can't say that I have actually consciously seen them - I only became aware of their field marks while preparing this article. The antelope jackrabbit is one of the largest hares in North America, weighing 9 to 10 pounds (4.5 kg). This jackrabbit’s huge ears are edged in white. The large eyes are placed high and towards the back of its slightly flattened head, allowing it to see nearly 360 degrees as it watches for predators. The antelope jackrabbit is so named because it has a patch of white fur on its flanks that it can flash on one side or the other as it zigs and zags, running from a predator, much as the pronghorn antelope does. (Arizona-Sonora Desert Museum-http://www.desertmuseum.org/books/nhsd_rabbits.php)

Antelope Jackrabbit photo by Rick Wright
According to literature, its prefered habitat is even dryer than that of the Black-tailed JR, which seems nearly impossible considering that we have Black-tails on our creosote flats. But its main distribution is more southern (Sonoran Desert in AZ and the western states of Mexico)  and it can reportedly deal better with extreme heat (Best and Henry, 1993).  It also prefers lower elevations than the Black-tailed, and  grassland to brush.

Antelope Jackrabbit flashing its white side. photo by A. Schmierer
So which jackrabbit flashed its white flanks? During my internet search for an image of the White-sided, I repeatedly found a misidentified Antelope JR, with white flanks, but clearly lacking the black on the inside of the ear tips. The San Rafael Valley is still rich in endigenous grasses that L. callotis likes, but the Canelo Hills location may be to high in elevation for the species. The photo by A. Schmierer, above, cleraly shows an Antelope JR, and it was taken in the Patagonia area which isn't far from the Canelo Hills. The White-sided JR is crepuscular to night-active. We saw the pair during the bright afternoon (but mating activity may disturb the pattern?) and the single one at dusk. We did see the flashing white flanks, but I paid no attention to the ears. So if Eric doesn't find his photos and they clearly show black ear tips, I think we will never know whether those were Antelope or White-sided Jackrabbits, but I now assume they were the former.


Old Jack.  watercolor M.Brummermann

Anyway, I think they are all amazing desert creatures, adapted to some of the most inhospitable habitats and chased and hunted by everyone from Golden Eagles and other raptors to felines, canines and humans, but still jumping, cavorting and playing.

All Ears. watercolor M. Brummermann

I found this in the AZ Star this morning and just couldn't help it, it just had to go on this blog:


When not able to find shelter, Lepus alleni can tolerate heat stress at high levels better and for a longer time than Lepus californicus. (Best and Henry, 1993; David S. Hinds, 1977; Mearns, 1890; Vorhies and Taylor, 1933)
When not able to find shelter, Lepus alleni can tolerate heat stress at high levels better and for a longer time than Lepus californicus. (Best and Henry, 1993; David S. Hinds, 1977; Mearns, 1890; Vorhies and Taylor, 1933)


 
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Wednesday, November 21, 2012

Color variations of the caterpillar of the White-lined Sphinx, Hyles lineata

In the summer of 2007 I witnessed mass migrations of caterpillars everywhere in Saguaro National Park West and Tucson Mountain Park. These cats were obviously sphingid larvae, complete with the characteristic horn on the hind end. But they came in many color variations and even the pattern varied between individuals. The reason behind the mass movement across paths and roads seemed to simply be that they had just devoured all herbaceous plants on their side of the road. I couldn't see any dominant direction. At the visitor center of SNPW I was shown a folder with images of local Moths that identified them as the larvae of the White-lined Sphinx.

Caterpillar and adult White-lined Sphinx
 At the time I was a very active member of the Arizona Star gallery for local photographers. For the next couple of years I noticed probably more submissions of images of the adult White-lined Sphinx than of any other butterfly or moth. When our friend Ingrid Schmidt from Germany spent a couple of weeks photographing our Tucson backyard fauna, we realized that we both knew the species from warm, sunny areas at the Mediterranean and even from southern Germany.

Der Kosmos Insektenfuehrer, by J.Zahradnik
 In fact, Hyles lineata (synonym Celerio lineata) ranges from Central America north through Mexico and the West Indies to most of the United States and southern Canada and also occurs in Eurasia and Africa. I think genetic studies may have to reveal whether all those populations are really in genetic exchange or whether separate species are forming.
Breeding twice annually between February and November Hyles lineata populations seem to go through cycles of population buildups and some sources assume that those trigger emigration and colonization of  more northern areas.
As caterpillars they consume a very wide variety of food plants from willow weed (Epilobium), four o'clock (Mirabilis), apple (Malus), evening primrose (Oenothera), elm (Ulmus), grape (Vitis), tomato (Lycopersicon), purslane (Portulaca), and Fuschia, also Rumex and Galium in Europe.

Hyles lineata nectaring on Cardinal Flower in Sycamore Canyon
 As adults they can be seen nectaring day and night on all kinds of deep-throated flowers. So they are able to adapt to many different habitats.

A dark caterpillar in Prescott
 While I witnessed the fist population explosion in the lower Sonoran Desert in 2007, I ran into another one in the mile-high town of Prescott (September of 2008) where they seemed to concentrate in riparian ares and the adults were so frequently seen on Saponaria  that some of my art show clients took me to see and identify them. 

In some years, H. lineata is not very common, but a few appear most nights. Peppersauce Canyon, Catalina Mts
 In August of 2009 Fred Skillman and I black-lighted north of Silver City New Mexico close to some meadows covered in Spotted Horsemint (Monarda punctata), and our black-lighting sheets were weight down by the on-slough of White-lined Sphinxes.   

Light colored caterpillar with pronounced back stripe, lower Sonoran Desert, Tucson
 But here in the desert around Tucson, the moths had become much rarer after several years of severe drought. I never see them anymore during the day on our Barrio Petunias that they used to love. But after somewhat better monsoon rains I did see more caterpillars on desert herbs.

These were all together in a patch of Mexican Prim Roses in Green Valley
 Last week, Lois O'Brien called me to  Green Valley to photograph caterpillars on her Mexican Prim Roses. She had a good number in her front yard and was fascinated by the extreme differences in their appearance. They ranged from bright juicy greens to nearly black, some had light median back stripes, others didn't, and there didn't seem to be any correlation between their size (age, instar) and those colors.  From the distribution of the caterpillars among the plants, we couldn't help but speculate that all these caterpillars came from a clutch of eggs from a single female.

Hyles lineata caterpillars at Saguaro National Park August 2007
When I came home, I went through my files and pulled out even more color variants. I came upon bright yellow ones with red markings from Tucson Mountain Park and dark and even blue and purple ones from Prescott. So is that a hint? Light colors on the sandy desert and darker ones in moister or colder environments? Thermoregulation? There seem to be some studies that support this theory.


In Lois' garden we noticed how difficult it was to find the big caterpillars in the flower beds. The dark colors were certainly very cryptic between the branches of the lush green plants while the bright green blended in with leaves in the sun. The great differences in appearance made it quite difficult to form a search image. Did you notice the smaller lime green caterpillar in the photo with the big yellow one? I should mention here that the colors do not seem to be aposematic. I had a young Jackdaw at home in Germany who seemed to like the caterpillars on his menu, and here in Tucson I watched even the notoriously seed-eating Northern Cardinal devouring every bit of a very fat one, which took several minutes and a couple of location changes to get away from Desert Museum visitors. I also remember a side-blotched lizard grabbing several small ones. So they are tasty.

A bad photo, but a great color variant from Prescott
 Considering the wide range of different habitats and the tendency of the adults to wander, isn't it possible that all the different patterns and colors occur randomly in the population or even a clutch (and I have no idea about the possible genetic base for this), and just a few will always get lucky and find camouflage and protection? The reason that I found more yellow ones in desert grasses and more dark ones in lusher, shadier places could just be the result of higher predation of the other colors.  In this scenario there would be selection, but no evolution in any direction, because the next generation may be growing up in a completely different habitat. During mass occurrences, the lack of a unified search image may make it more difficult for predators 'to get them all'.  I for example keep overlooking some color morphs in my own photos.
  




Friday, November 2, 2012

Egg Sacks and Gossamer Showers



Around Halloween, spider webs are not just artificial decorations around human homes but a very obvious part of the natural world. Many big spiders seem to mature at a time when most insects are close to the end of their lives.  In autumn the spiders can easily harvest weakened bees, beetles and grasshoppers that might have been able to put up too much of a struggle in their prime.  This abundance of prey provides spiders with resources to survive the lean winter months. The term survival doesn't refer to the individual here. Many spiders mature and produce eggs in autumn, and it is often only the offspring that winters, be it in form of eggs or as freshly hatched spiderlings. But it certainly pays to send these off very well nourished.


Peucetia viridans (Green Lynx Spider) preying on a bee
Not all spider weavings are hunting implements. Lynx spiders do not trap their prey in webs. They get their name from their hunting methods that include stalking, jumping,  and sometimes lengthy pursuits of the prey and reminded observers of those of a big cat. Lynx Spiders are well equipped for this kind of hunting with strong legs and streamlined bodies.

 Their translucent green color of Peucetia viridans (Green Lynx Spider) may be cryptic enough to hide them from their prey when they lay in ambush on green foliage.  But when they stalk their prey on flowers as they very often do, they seem very obvious at least to the human eye and far less camouflaged than the yellow and white crab spiders that are also hunting for flower visitors.


By late October the female lynx spiders reach maturity and are quite big, three fourth of an inch. They produce a ball of webbing that is about the size of a quarter and suspended from tall grasses or twigs of a mesquite or acacia. 


The ball is the egg sac of the spider that she guards carefully. It contains hundreds of eggs  Interestingly,  in this case there was also silk-wrapped prey, namely a honey bee, in this nesting area. I wonder whether the female, duty-bound to the nest as she is, is now routinely trapping insects for food, or whether she just opportunistically collects when something gets caught. Are any of the threads sticky? I think I have to research what is known about the phylogenesis of spider webs as traps. Maybe they did all evolve from nesting webs which are not uncommon among arthropods.


 This spider is guarding her freshly hatched spiderlings in the mesquite grassland around Molino Basin. Bynow her egg sack is loosing its tightly woven  coherence.


 Hundreds of young spiders will soon be pouring out of this one egg sack. It looks as if they go through one molt before they move on, as many exuviae are still hanging in the nest.

 By mid November the kids have grown and the female has lost a lot of weight.


Peucetia viridans (Green Lynx Spider)  with hatchlings, photo added in Nov. 2014
To find food and survive, the hatchlings will now have to disperse.  Their tiny legs are not a great means of locomotion, even though each has eight of them.  

Juvenile wolf spider ready for take-off  (photo by Pieceoflace Photohraphy)

Instead, like dandelion seeds, many young spiders use aerial navigation:  Each spider climbs the top of a grass or a twig. Here the spider lifts up its abdomen and spins out a thread, long enough to buoy up the spider. A mild upward air current of a still autumn day would be ideal to carry the silk and the attached little spider far enough to begin her live on her own.  

Gossamer Sunset (photo by DavidMXGreen@gmail.com)
Threads of millions of little spider floating in the wind can form showers of silvery gossamer. If they all get caught in the same area they can form veils that cover soil and vegetation in magically sparkling layers. In Germany this time of the year is called Altweibersommer, 'old wives' summer for its flying silvery threads.